PHILIPS 14CT3405 CAMPIGLI CHASSIS KT30 TRD is a Fully Modular chassis. A big Well done for a 14 Inches Color portable set.
This is replacing the previous series based on the PHILIPS CHASSIS KT2.
This is the PHILIPS KT3 which was used in set from 16 to 20 Inches screen format types.
Mains rectifier 8222 280 2097.3
Supply control With TDA2581q (PHILIPS) 8222 280 2089.6
IF DEM Unit with TDA2540q (PHILIPS) 3122 128 80281 8222 280 2109.4
Synch with TDA2571AQ (PHILIPS) 8222 280 2105.4
Lum + Chrom with TDA 2525Q AND TDA2560/3Q + Delay Line DL 700. 8222 280 2093.3
RGB OUTPUT 8222 280 2101.4
SOUND With TBA120AS 8222 280 2082.6
TBA120T (Siemens) SIF (S
PHILIPS Chassis KT30 detailed view.
Supply + line + EHT Stages
Focus + G2 + E/W Correction - FRAME Deflection.
Signal Stages (Chroma + Luma + Sound + RGB + Synch + IF + RF Tuner)
Line deflection output transistor (BU208A)
The Philips KT3 and K30 K35
chassis have been used in Pye and Philips colour sets from 1979-1980
to 1983. They are of modular construction, consisting of seven plug-in
daughter boards units mounted on a main mother panel. The KT3 is
designed to drive Philips 90° in -line gun tubes with screen sizes up to
20in. Its big screen sister, the K30, drives 110° 30AX tubes in 22 and
26in. screen sizes. Apart from this the two chassis are electrically
very similar, the main differences being associated with the line output
stage: the KT3 uses a line output transformer plus tripler powered from
a 129V h.t. rail, whilst the K30 has a diode -split line output
transformer and 140V h.t. rail. The modules are for the most part
directly interchangeable, the exceptions being the chopper control and
sound panels. There have been two versions of each chassis. The 1982
versions are known as "edition II". They incorporate slight changes in
the mother panel and a completely redesigned decoder panel which is not
interchangeable with the earlier panel. The new decoder panel has a
single PHILIPS TDA3560 chip whilst the earlier panel uses a TDA2560Q and
a TDA2523Q. In addition an improved power supply (chopper control)
panel, type BY02, has been introduced. It's a direct replacement for the
previous panels. To service a panel "in situ", a module extension board
is required (part number 39537085). The KT3 and K30 chassis have proved
to be extremely reliable, so there's only a limited fault history. Our
experiences to date are summarised below.Random Tripping;
Because of the high sensitivity of the power supply, look for dry joints etc. rather than a faulty component. Usual causes are as follows. Incorrect h.t. setting - the h.t. can be conveniently measured at pins 2 or 4 of the line scan coils connector M5. The e.h.t. lead not being pushed hom
e
fully into the line output transformer (K30 chassis only). Dirt or
grease (e.g. cigarette tarnish) around the e.h.t. cap, focus unit or the
printed c.r.t. spark gaps - clean with a suitable solvent, e.g. alcool.
If necessary, carry out the following modifications: change R7354 from
27042 to 56052 (at the same time, if there's a resistor in parallel with
R1461, remove it); fit (if not there already) an 0.1μF capacitor
(C7337) between pin 12 of IC7322 (TDA2581Q) and the base of T7336
(BC558).Tripping:
If the set trips three minutes after switching on, check the efficiency diode (D1464) in the chopper circuit. It should be type BY208 in the KT3 chassis and type BYX55-600 in the K30. If it's running warm or of incorrect type, replace it. If there's permanent tripping (ticking), disconnect the line scan connector M5 to isolate the line output stage. If the tripping stops and the h.t. is correct, check the tripler (KT3), the line output transistor T1562 (BU205 KT3, BU208A K30), and the EW modulator diodes D1562 and D1567. D1567 is type BY228 in both chassis; D1562 is type BY208 in the KT3, type BYX55-600 in the K30. If necessary check the line output transformer. If the tripping persists with M5 disconnected, i.e. the h.t. voltage is varying, the fault is in the power supply Check the chopper transistor T1463 (BUW84 KT3, BU426V K30), the efficiency diode D1464 (see above) and the chopper control panel by substitution.
Dead Set:
If the fuses have blown, replace the BY227 bridge rectifier diodes D6292/4/5/6 and of course the fuses - 2A delay types. If some 300V is present across the bridge rectifier's reservoir capacitor C1460a (part of the electrolytic can C1460a/b/c), check the h.t. at C1460c. If the reading is 300V, the chopper transistor T1463 is short-circuit. If the reading is zero, either the chopper transistor is duff or it's not being switched on. In the latter event, check first whether the 12V output from the rectifier panel is present at point 10 on this panel - or is less than 9V. If this supply is correct and is reaching point 12 on the chopper control panel, the latter is faulty. The usual offenders on the chopper control panel are the 6.8V zener diode D7343 (type BZX79-B6V8 - check for 6.8V at pin 10 of the i.c.) and the TDA2581Q chip itself (IC7322). If necessary carry out cold resistance component checks. The TDA2581Q chip provides protection under the following conditions: voltage at pin 7 higher than 6.8V (over -voltage protection); the pulse amplitude at pin 6 exceeds -0.6V (excess -current protection); voltage at pin 9 less than 9V (low i.c. supply); voltage at pin 10 exceeds 8.2V (excessive reference voltage, i.e. the zener diode D7343 is open -circuit); the voltage at pin 5 is 5V (this is the stand-by facility).
No Raster:
Check whether the orange plug has dropped off the focus unit (K30 only). In both the KT3 and the K30 chassis, the c.r.t.'s first anode supply/supplies are derived from the earthy side of the 24Mi2 focus potentiometer. Check whether the surge limiter R1590 in the 30/32V supply is open -circuit. This line output transformer derived supply is used by the field driver and output stages. It also biases off the field flyback blanking transistor T1535 (BC558) during the field scan, so its absence leaves this transistor hard on and no raster. Field Collapse If the 30/32V supply is missing (30V in the KT3 chassis, 32V in the K30), it's usually necessary to replace the surge limiter resistor R1590 (3.352 KT3, 1.2(1 K30), the two transistors in the field output stage, and their emitter resistors R1531/2. The resistors are 0.5W safety types, value 1.5n. The transistors are BD223/BD234 (T1530/T1532) in the KT3, BD437/BD438 (T1530/T1532) in the K30. Also check the field scan coupling capacitor C1521 (470μF KT3, 1500μF K30). Other causes of field collapse (30/32V supply o.k.) are cracks in the print around the edge of the mother board near the field driver and output stages or a faulty field oscillator (this is on the sync panel).
Field Linearity:
If poor, check by replacement the following feedback capacitors: C1522 (220μF) and C1541 (0.056μF). Check whether the feedback resistor R1502 is open -circuit (1551, 0.25W safety type).
Sync Faults:
In the event of a rolling picture, replace all four transistors on the sync panel - T8386 (BC548), T8392 (BC548B), T8397 (BC558) and T8396 (BC548C). Only when the line sync is also poor is the TDA2571AQ sync i.c. suspect. Teletext Sets On teletext (Mk. II) KT3 and K30 K35 sets the teletext power panel at the base of the cabinet seems to be vulnerable to transit damage - you can get badly cracked panels. Failure of the 5V regulator IC1007 (MC7805CT) that supplies the teletext decoder panel results in complete loss of sync.
No Sound:
Make sure the customer hasn't switched off the loudspeaker - a muting switch is fitted on the front in most sets. Next check whether the supply is present at point 12 on the sound module. This is 20V in the KT3, 28V in the K30, and comes from a chopper transformer fed rectifier on the bridge rectifier panel. If the supply is absent, check R1413 (4 .71/ KT3, 8.252K30) and if necessary R6303 (2.2(1) on the bridge rectifier panel. Failure of these resistors is almost always due to a duff TDA2611AQ audio output i.c. (IC5181). If the supply is present, apply a signal (your finger on a screwdriver blade will do) at pin 7 of IC5181. If a hum is heard, the audio i.c. is o.k. and the most likely culprit is the TBA120AS intercarrier sound i.c. (IC5164).
Tone sound Sibilanc
e:Some customers complain that their sets suffer from excessive treble/sibilance, particularly those fitted with the KT3 chassis. This is not a fault in itself, but an improvement can be obtained by increasing the value of the de emphasis capacitor C5177 to 0.039μF as in production.
The Cabinet:
I've always found it best and safest to glue the front surround to the cabinet and use a sufficient quantity of self -tapping or wood screws of suitable length.
White Raster:
If there's a flooded white raster with the brightness and contrast controls having no effect, you will probably find that the 155V line filter resistor 81456 (1000 safety) is open -circuit due to a short-circuit transistor in one of the RGB output stages. Use cold resistance checks on the RGB panel as the voltage readings obtained are often confusing, then replace as necessary. In the edition II version of the KT3 R1456 becomes R1587. never more than a quarter of a turn.
No problems have been experienced with the i.f. module to date except for over aged capacitors which barely fail.
Poor HF Resolution:
If the picture is not as sharp as it could be, a fractional adjustment of the tuner's i.f. output coil is required
Tuner:
The U321 tuner unit should be replaced if the fault is low gain, cross modulation, etc.
PHILIPS 14CT3405 CAMPIGLI CHASSIS KT3 TRD CIRCUIT ARRANGEMENT IN A PICTURE DISPLAY DEVICE UTILIZING A STABILIZED SUPPLY VOLTAGE CIRCUIT:
Line synch Switched Mode Power Supply with Line deflection output Transistor Drive Circuit:A stabilized supply voltage circuit for a picture display device comprising a chopper wherein the switching signal has the line frequency and is duration-modulated. The coil of the chopper constitutes the primary winding of a transformer a secondary winding of which drives the line output transistor so that the switching transistor of the chopper also functions as a driver for the line output stage. The oscillator generating the switching signal may be the line oscillator. In a special embodiment the driver and line output transistor conduct simultaneously and in order to limit the base current of the line output transistor a coil shunted by a diode is incorporated in the drive line of the line output transistor. Other secondary windings of the transformer drive diodes which conduct simultaneously with the efficiency diode of the chopper so as to generate further stabilized supply voltages.
1.
An electrical circuit arrangement for a picture display device
operating at a given line scanning frequency, comprising a source of
unidirectional voltage, an inductor, first switching transistor means
for periodically energizing said inductor at said scanning frequency
with current from said source, an electrical load circuit coupled to
said inductor and having applied thereto a voltage as determined by the
ratio of the ON and OFF periods of said transistor, means for
maintaining the voltage across said load circuit at a given value
comprising means for comparing the voltage of said load circuit with a
reference voltage, means responsive to departures of the value of the
load circuit voltage from the value of said reference voltage for
varying the conduction ratio of the ON and OFF periods of said
transistor thereby to stabilize said load circuit voltage at the given
value, a line deflection coil system for said picture display device,
means for energizing said line deflection coil system from said load
voltage circuit means, means for periodically interrupting the
energization of said line deflection coil comprising second switching
means and means coupled to said inductor for deriving therefrom a
switching current in synchronism with the energization periods of said
transistor and applying said switching current to said switching means
thereby to actuate the same, and means coupled to said switching means
and to said load voltage circuit for producing a voltage for energizing
said 2. A circuit as claimed in claim 1 wherein the duty cycle of said
switching 3. A circuit as claimed in claim 1 further comprising an
efficiency first 4. A circuit as claimed in claim 3 further comprising
at least a second diode coupled to said deriving means and to ground,
and being poled to 5. A circuit as claimed in claim 1 wherein said
second switching means comprises a second transistor coupled to said
deriving means to conduct simultaneously with said first transistor, and
further
comprising a coil coupled between said driving means and said second
transistor and a third diode shunt coupled to said coil and being poled
to conduct when said 6. A circuit as claimed in claim 1 further
comprising a horizontal oscillator coupled to said first transistor,
said oscillator being the 7. A circuit as claimed in claim 1 further
comprising means coupled to said inductor for deriving filament voltage
for said display device. 
Description:
The
invention relates to a circuit arrangement in a picture display device
wherein the input direct voltage between two input terminals, which is
obtained be rectifying the mains alternating voltage, is converted
into a stabilized output direct voltage by means of a switching
transistor and a coil and wherein the transistor is connected to a
first input terminal and an efficiency diode is connected to the
junction of the transistor and the coil. The switching transistor is
driven by a pulsatory voltage of line frequency which pulses are
duration-modulated in order to saturate the switching transistor during
part of the period dependent on the direct voltage to be stabilized and
to cut off this transistor during the remaining part of the period.
The pulse duration modulation is effected by means of a comparison
circuit which compares the direct voltage to be stabilized with a
substantially constant voltage, the coil constituting the primary
winding of a transformer.
Such a circuit arrangement
is known from German "Auslegeschrift" 1.293.304. wherein a circuit
arrangement is described which has for its object to convert an input
direct voltage which is generated between two terminals into a
different direct voltage. The circuit employs a switch connected to the
first terminal of the input voltage and periodically opens and closes
so that the input voltage is converted into a pulsatory voltage. This
pulsatory voltage is then applied to a coil. A diode is arranged
between the junction of the switch and the coil and the second terminal
of the input voltage whilst a load and a charge capacitor in parallel
thereto are arranged between the other end of the coil and the second
terminal of the input voltage. The assembly operates in accordance with
the known efficiency principle i.e., the current supplied to the load
flows alternately through the switch and through the diode. The
function of the switch is performed by a switching transistor which is
driven by a periodical pulsatory voltage which saturates this
transistor for a given part of the period. Such a configuration is
known under different names in the literature; it will be referred to
herein as a "chopper." A known advantage thereof, is that the switching
transistor must be able to stand a high voltage or provide a great
current but it need not dissipate a great power. The output voltage of
the chopper is compared with a constant reference voltage. If the
output voltage attempts to vary because the input voltage and/or the
load varies, a voltage causing a duration modulation of the pulses is
produced at the output of the comparison arrangement. As a result the
quantity of the energy stored in the coil varies and the output voltage
is maintained constant. In the German "Auslegeschrift" referred to it
is therefore an object to provide a stabilized supply voltage device.
In the circuit arrangement according to the mentioned German "Auslegeschrift" the frequency of the load variations or a harmonic thereof is chosen as the frequency for the switching voltage. Particularly when the load fed by the chopper is the line deflection circuit of a picture display device, wherein thus the impedance of the load varies in the rhythm of the line frequency, the frequency of the switching voltage is equal to or is a multiple of the line frequency.
It
is to be noted that the chopper need not necessarily be formed as that
in the mentioned German "Auslegeschrift." In fact, it is known from
literature that the efficiency diode and the coil may be exchanged. It
is alternatively possible for the coil to be provided at the first
terminal of the input voltage whilst the switching transistor is
arranged between the other end and the second terminal of the input
voltage. The efficiency diode is then provided between the junction of
said end and the switching transistor and the load. It may be recognized
that for all these modifications a voltage is present across the
connections of the coil which voltage has the same frequency and the
same shape as the pulsatory switching voltage. The control voltage of a
line deflection circuit is a pulsatory voltage which causes the line
output transistor to be saturates and cut off alternately. The invention
is based on the recognition that the voltage present across the
connections of the coil is suitable to function as such a control
voltage and that the coil constitutes the primary of a transformer. To
this end the circuit arrangement according to the invention is
characterized in that a secondary winding of the t
ransformer
drives the switching element which applies a line deflection current
to line deflection coils and by which the voltage for the final anode
of a picture display tube which forms part of the picture display
device is generated, and that the ratio between the period during which
the switching transistor is saturated and the entire period, i.e., the
switching transistor duty cycle is between 0.3 and 0.7 during normal
operation.
The invention is also based on the
recognition that the duration modulation which is necessary to
stabilize the supply voltage with the switching transistor does not
exert influence on the driving of the line output transistor. This
resides in the fact that in case of a longer or shorter cut-off period
of the line output transistor the current flowing through the line
deflection coils thereof is not influenced because of the efficiency
diode current and transistor current are taken over or, in case of a
special kind of transistor, the collector-emitter current is taken over
by the base collector current and conversely. However, in that case
the above-mentioned ratios of 0.3 : 0.7 should be taken into account
since otherwise this take-over principle is jeopardized.
As will be further explained the use of the switching transistor as a driver for the line output transistor in an embodiment to be especially described hereinafter has the further advantage that the line output transistor automatically becomes non-conductive when this switching transistor is short circuited so that the deflection and the EHT for the display tube drop out and thus avoid damage thereof.
Due to the step according to the invention the switching transistor in the stabilized supply functions as a driver for the line deflection circuit. The circuit arrangement according to the invention may in addition be equipped with a very efficient safety circuit so that the reliability is considerably enhanced, which is described in the U.S. Pat. No. 3,629,686. The invention is furthermore based on the recognition of the fact that the pulsatory voltage present across the connections of the coil is furthermore used and to this end the circuit arrangement according to the invention is characterized in that secondary windings of the transformer drive diodes which conduct simultaneously with the efficiency diode so as to generate further stabilized direct voltages, one end of said diodes being connected to ground.
In order that the invention may be readily carried into effect, a few embodiments thereof will now be described in detail by way of example with reference to the accompanying diagrammatic drawings in which:
FIG. 1 shows a principle circuit diagram wherein the chopper and the line deflection circuit are further shown but other circuits are not further shown.
FIGS. 2a, 2b and 2c show the variation as a function of time of two currents and of a voltage occurring in the circuit arrangement according to FIG. 1.
FIGS. 3a 3b, 3c and 3d show other embodiments of the chopper.
FIGS. 4a and 4b show modifications of part of the circuit arrangement of FIG. 1.
In
FIG. 1 the reference numeral 1 denotes a rectifier circuit which
converts the mains voltage supplied thereto into a non-stabilized direct
voltage. The collector of a switching transistor 2 is connected to one
of the two terminals between which this direct voltage is obtained,
said transistor being of the npn-type in this embodiment and the base
of which receives a pulsatory voltage which originates through a
control stage 4 from a modulator 5 and causes transistor 2 to be
saturated and cut off alternately. The voltage waveform 3 is produced
at the emitter of transistor 2. In order to maintain the output voltage
of the circuit arrangement constant, the duration of the pulses
provided is varied in modulator 5. A pulse oscillator 6 supplies the
pulsatory voltage to modulator 5 and is synchronized by a signal of
line frequency which originates from the line oscillator 6' present in
the picture display device. This line oscillator 6' is in turn directly
synchronized in known manner by pulses 7' of line frequency which are
present in the device and originate for example from a received
television signal if the picture display device is a television
receiver. Pulse oscillator 6 thus generates a pulsatory voltage the
repetition frequency of which is the line frequency.
The
emitter of switching transistor 2 is connected at one end to the
cathode of an efficiency diode 7 whose other end is connected to the
second input voltage terminal and at the other end to primary winding 8
of a transformer 9. Pulsatory voltage 3 which is produced at the
cathode of efficiency diode 7 is clamped against the potential of said
second terminal during the intervals when this diode conducts. During
the other intervals the pulsatory voltage 3 assumes the value V i .
A charge capacitor 10 and a load 11 are arranged between the other end
of winding 8 and the second input voltage terminal. The elements
2,7,8,10 and 11 constitute a so-called chopper producing a direct
voltage across charge capacitor 10, provided that capacitor 10 has a
sufficiently great value for the line frequency and the current applied
to load 11 flowing alternately through switching transistor 2 or
through efficiency diode 7. The output voltage V o which is
the direct voltage produced across charge capacitor 10 is applied to a
comparison circuit 12 which compares the voltage V o with a
reference voltage. Comparison circuit 12 generates a direct voltage
which is applied to modulator 5 so that the duration of the effective
period δ T of switching transistor 2 relative to the period T of pulses
3 varies as a function of the variations of output voltage V 0 . In fact, it is readily evident that output voltage V o is proportional to the ratio δ :
V o = V i . δ
Load 11 of the chopper consists in the consumption of parts of the picture display device which are fed by output volt
age V 0 .
In a practical embodiment of the circuit arrangement according to FIG.
1 wherein the mains alternating voltage has a nominal effective value
of 220 V and the rectified voltage V i is approximately 270 V, output voltage V o
for δ = 0.5 is approximately 135 V. This makes it also possible, for
example, to feed a line deflection circuit as is shown in FIG. 1 wherein
load 11 then represents different parts which are fed by the chopper.
Since voltage V o is maintained constant due to pulse
duration modulation, the supply voltage of this line deflection circuit
remains constant with the favorable result that the line amplitude(=
the width of the picture displayed on the screen of the picture display
tube) likewise remains constant as well as the EHT required for the
final anode of the picture display tube in the same circuit arrangement
independent of the variations in the mains voltage and the load on the
EHT generator (= variations in brightness).
However,
variations in the line amplitude and the EHT may occur as a result of
an insufficiently small internal impedance of the EHT generator.
Compensation means are known for this purpose. A possibility within the
scope of the present invention is to use comparison circuit 12 for this
purpose. In fact, if the beam current passes through an element having
a substantially quadratic characteristic, for example, a
voltage-dependent resistor, then a variation for voltage V o
may be obtained through comparison circuit 12 which variation is
proportional to the root of the variation in the EHT which is a known
condition for the line amplitude to remain constant.
In addition this facilitates smoothing of voltage V o since the repetition frequency of pulsatory voltage 3 is many times higher than that of the mains and a comparatively small value may be sufficient for charge capacitor 10. If charge capacitor 10 has a sufficiently high value for the line frequency, voltage V o is indeed a direct voltage so that a voltage having the same form as pulsatory voltage 3 is produced across the terminals of primary winding 8. Thus voltages which have the same shape as pulsatory voltage 3 but have a greater or smaller amplitude are produced across secondary windings 13, 14 of transformer 9 (FIG. 1 shows only 2 secondary windings but there may be more). The invention is based on the recognition that one end of each secondary winding is connected to earth while the other end thereof drives a diode, the winding sense of each winding and the direction of conductance of each diode being chosen to be such that these diodes conduct during the same period as does efficiency diode 7. After smoothing, stabilized supply voltages, for example, at terminal 15 are generated in this manner at the amplitudes and polarities required for the circuit arrangements present in the picture display device. In FIG. 1 the voltage generated at terminal 15 is, for example, positive relative to earth. It is to be noted that the load currents of the supply voltages obtained in this manner cause a reduction of the switching power which is economized by efficiency diode 7. The sum of all diode currents including that of diode 7 is in fact equal to the current which would flow through diode 7 if no secondary winding were wound on transformer 9 and if no simultaneous diode were used. This reduction may be considered an addit
ional
advantage of the circuit arrangement according to the invention, for a
diode suitable for smaller powers may then be used. However, it will be
evident that the overall secondary load must not exceed the primary
load since otherwise there is the risk of efficiency diode 7 being
blocked so that stabilization of the secondary supply voltages would be
out of the question.
It is to be noted that a parabola voltage of line frequency as shown at 28 is produced across the charge capacitor 10 if this capacitor is given a smaller capacitance so that consequently the so-called S-correction is established.
In FIG. 1 charge capacitors are arranged between terminals 15 etc. and earth so as to ensure that the voltages on these points are stabilized direct voltages. If in addition the mean value of the voltage on one of these terminals has been made equal to the effective value of the alternating voltage which is required for heating the filament of the picture display tube present in the picture display device, this voltage is suitable for this heating. This is a further advantage of the invention since the cheap generation of a stabilized filament voltage for the picture display tube has always been a difficult problem in transistorized arrangements.
A further advantage of the picture display device according to the invention is that transformer 9 can function as a separation transformer so that the different secondary windings can be separated from the mains and their lower ends can be connected to ground of the picture display device. The latter step makes it possible to connect a different apparatus such as, for example, a magnetic recording and/or playback apparatus to the picture display device without earth connection problems occurring.
In FIG. 1 the reference numeral 14 denotes a secondary winding of transformer 9 which in accordance with the previously mentioned recognition of the invention can drive line output transistor 16 of the line deflection circuit 17. Line deflection circuit 17 which is shown in a simplified form in FIG. 1 includes inter alia line deflection coils 18 and an EHT transformer 19 a secondary winding 20 of which serves for generating the EHT required for the acceleration anode of the picture display tube. Line deflection circuit 17 is fed by the output voltage V o of the chopper which voltage is stabilized due to the pulse duration modulation with all previously mentioned advantages. Line deflection circuit 17 corresponds, for example, to similar arrangements which have been described in U.S. Pat. No. 3,504,224 issued Mar. 31, 1970 to J.J. Reichgelt et al., U.S. patent application Ser. No. 737,009 filed June 14, 1968 by W. H. Hetterscheid and U.S. application Ser. No. 26,497 filed April 8, 1970 by W. Hetterscheid et al. It will be evident that differently formed lined deflection circuits are alternatively possible.
It will now be shown that secondary winding 14 can indeed drive a line deflection circuit so that switching transistor 2 can function as a driver for the line deflection. FIGS. 2a and b show the variation as a function of time of the current i C which flows in the collector of transistor 16 and of the drive voltage v 14 across the terminals of secondary winding 14. During the flyback period (0, t 1 ) transistor 16 must be fully cut off because a high voltage peak is then produced at its collector; voltage v 14 must then be absolutely negative. During the scan period (t 1 , t 4 ) a sawtooth current i C flows through the collector electrode of transistor 16 which current is first negative and then changes its direction. As the circuit arrangement is not free from loss, the instant t 3 when current i C becomes zero lies, as is known, before the middle of the scan period. At the end t 4 of the scan period transistor 16 must be switched off again. However, since transistor 16 is saturated during the scan period and since this transistor must be suitable for high voltages and great powers so that its collector layer is thick, this transistor has a very great excess of charge carriers in both its base and collector layers. The removal of these charge carriers takes a period t s which is not negligible whereafter the transistor is indeed switched off. Thus the fraction δ T of the line period T at which v 14 is positive must end at the latest at the instant (t 4 - t s ) located after the commencement (t = 0) of the previous flyback.
The time δ T may be initiated at any instant t 2 which is located between the end t 1 of the flyback period and the instant t 3 when collector current i C reverses its direction. It is true that emitter current flows through transistor 16 at the instant t 2 , but collector current i C is not influenced thereby, at least not when the supply voltage (= V o ) for line deflection circuit 17 is high enough. All this has been described in the U.S. Pat. No. 3,504,224. The same applies to line deflection circuits wherein the collector base diode does not function as an efficiency diode as is the case in the described circuit 17, but wherein an efficiency diode is arranged between collector and emitter of the line output transistor. In such a case the negative part of the current i C of FIG. 2a represents the current flowing through the said efficiency diode.
After the instant t 3 voltage v 14 must be positive. In other words, the minimum duration of the period T when voltage v 14 must be positive is (t 4 - t s ) - t 3 whilst the maximum duration thereof is (t 4 - t s ) - t 1 . In a television system employing 625 lines per raster the line period t 4 is approximately 64 μus and the flyback period is approximately 12 μus. Without losses in the circuit arrangement instant t 3 would be located approximately 26 μus after the instant t 1 , and with losses a reasonable value is 22 μus which is 34 μus after the commencement of the period. If for safety's sake it is assumed that t s lasts approximately 10 μus, the extreme values of δ T are approximately 20 and 42 μus and consequently the values for δ are approximately 0.31 and 0.66 at a mean value which is equal to approximately 0.49. It was previously stated that a mean value of δ = 0.5 was suitable. Line deflection circuit 17 can therefore indeed be used in combination with the chopper in the manner described, and the relative variation of δ may be (0.66 - 0.31) : 0.49 = 71.5 percent. This is more than necessary to obviate the variations in the mains voltage or in the various loads and to establish the East-West modulation and ripple compensation to be described hereinafter. In fact, if it is assumed that the mains voltage varies between -15 and +10 percent of the nominal value of 220 V, while the 50 Hz ripple voltage which is superimposed on the input voltage V i has a peak-to-peak value of 40 V and V i is nominally 270 V, then the lowest occurring V i is:
0.85 × 270 V - 20 V = 210 V and the highest occurring V i is
1.1 × 270 V + 20 V = 320 V. For an output voltage V o of 135 V the ratio must thus vary between
δ = 135 : 210 = 0.64 and δ = 135 : 320 = 0.42.
A considerable problem presenting itself is that of the simultaneous or non-simultaneous drive of line output transistor 16 with switching transistor 2, it being understood that in case of simultaneous drive both transistors are simultaneously bottomed, that is during the period δ T. This depends on the winding sense of secondary winding 14 relative to that of primary winding 8. In FIG. 1 it has been assumed that the drive takes place simultaneously so that the voltage present across winding 14 has the shape shown in FIG. 2b. This voltage assumes the value n(V i - V o ) in the period δ T and the value -nVo in the period (1 - δ )T, wherein n is the ratio of the number of turns on windings 14 and 8 and wherein V o is maintained constant at nominal mains voltage V o = δ V inom . However, if as a result of an increase or a decrease of the mains voltage V i increases or decreases proportionally therewith, i.e., V i = V i nom + Δ V, the positive portion of V 14 becomes equal to n(V i nom - V o +Δ V) = n [(1 -δ)V i nom +ΔV] = n(0.5 V inom +ΔV) if δ = 0.5 for V i = V i nom. Relatively, this is a variation which is twice as great. For example, if V i nom = 270 V and V o = 135 V, a variation in the mains voltage of from -15 to +10 percent causes a variation of V i of from -40.5 V to +27 V which ranges from -30 to +20 percent of 135 V which is present across winding 8 during the period δ T. The result is that transistor 16 can always be bottomed over a large range of variation. If the signal of FIG. 2b would be applied through a resistor to the base of transistor 16, the base current thereof would have to undergo the same variation while the transistor would already be saturated in case of too low a voltage. In this case it is assumed that transformer 9 is ideal (without loss) and that coil 21 has a small inductance as is explained in the U.S. patent application Ser. No. 737,009 above mentioned. It is therefore found to be desirable to limit the base current of transistor 16.
This
may be effected by providing a coil 22 having a large value
inductance, approximately 100 μH, between winding 14 and the small coil
21. The variation of said base current i b is shown in
FIG. 2c but not to the same scale as the collector current of FIG. 2a.
During the conducting interval δ T current i b varies as a
linear function of time having a final value of wherein L represents
the inductance of coil 22. This not only provides the advantage that
this final value is not immediately reached, but it can be shown that
variation of this final value as a function of the mains voltage has
been reduced, for there applies at nominal mains voltage that: If the
mains voltage V i = V i nom +Δ V, then ##SPC1## because V i nom = 2 V o . Thus this variation is equal to that of the mains voltage and is not twice as great.
During switching off, t 2 ,
of transistor 16 coil 22 must exert no influence and coil 21 must
exert influence which is achieved by arranging a diode 23 parallel to
coil 22. Furthermore the control circuit of transistor 16 in this
example comprises the two diodes 24 and 25 as described in U.S.
application Ser. No. 26,497 above referred to, wherein one of these
diodes, diode 25 in FIG. 1, must be shunted by a resistor.
The control circuit of transistor 16 may alternatively be formed as is shown in FIG. 4. In fact, it is known that coil 21 may be replaced by the parallel arrangement of a diode 21' and a resistor 21" by which the inverse current can be limited. To separate the path of the inverse current from that of the forward current the parallel arrangement of a the diode 29' and a resistor 29" must then be present. This leads to the circuit arrangement shown in the upper part of FIG. 4. This circuit arrangement may now be simplified if it is noted that diodes 25 and 21' on the one hand and diodes 23 and 29' on the other hand are series-arranged. The result is shown in the lower part of FIG. 4 which, as compared with the circuit arrangement of FIG. 1, employs one coil less and an additional resistor.
FIG. 3 shows possible modifications of the chopper. FIG. 3a shown in a simplified form the circuit arrangement according to FIG. 1 wherein the pulsatory voltage present across the connections of windings 8 has a peak-to-peak amplitude of V i - V o = 0.5 V i for δ = 0.5, As has been stated, the provision of coil 22 gives a relative variation for the base current of transistor 16 which is equal to that of the mains voltage. In the cases according to FIG. 3b, 3c and 3d the peak-to-peak amplitude of the voltage across winding 8 is equal to V i so that the provision of coil 22 results in a relative variation which is equal to half that of the mains voltage which is still more favorable than in the first case.
Transistors
of the npn type are used in FIG. 3. If transistors of the pnp type are
used, the relevant efficiency diodes must of course be reversed.
In this connection it is to be noted that it is possible to obtain an output voltage V o with the aid of the modifications according to FIGS. 3b, c and d, which voltage is higher than input voltage V i . These modifications may be used in countries such as, for example, the United of America or France where the nominal mains voltage is 117 or 110 V without having to modify the rest of the circuit arrangement.
The above-mentioned remark regarding the sum of the diode currents only applies, however, for the modifications shown in FIGS. 3a and d.
If line output transistor 16 is not simultaneously driven with switching transistor 2, efficiency diodes 7 conducts simultaneously with transistor 16 i.e., during the period which is denoted by δ T in FIGS. 1 and 2b. During that period the output voltage V o of the chopper is stabilized so that the base current of transistor 16 is stabilized without further difficulty. However, a considerable drawback occurs. In FIG. 1 the reference numeral 26 denotes a safety circuit the purpose of which is to safeguard switching transistor 2 when the current supplied to load 11 and/or line deflection circuit 17 becomes to high, which happens because the chopper stops. After a given period output voltage V o is built up again, but gradually which means that the ratio δ is initially small in the order of 0.1. All this is described in U.S. patent No. 3,629,686. The same phenomenon occurs when the display device is switched on. Since δ = 0.1 corresponds to approximately 6 μs when T = 64 μs, efficiency diode 7 conducts in that case for 64 - 6 = 58 μus so that transistor 16 is already switched on at the end of the scan or at a slightly greater ratio δ during the flyback. This would cause an inadmissibly high dissipation. For this reason the simultaneous drive is therefore to be preferred.
The line deflection circuit itself is also safeguarded: in fact, if something goes wrong in the supply, the driver voltage of the line deflection circuit drops out because the switching voltage across the terminals of primary winding 8 is no longer present so that the deflection stops. This particularly happens when switching transistor 2 starts to constitute a short-circuit between emitter and collector with the result that the supply voltage V o for the line deflection circuit in the case of FIG. 1 becomes higher, namely equal to V i . However, the line output transformer is now cut off and is therefore also safe as well as the picture display tube and other parts of the display device which are fed by terminal 15 or the like. However, this only applies to the circuit arrangement according to FIG. 1 or 3a.
Pulse
oscillator 6 applies pulses of line frequency to modulator 5. It may
be advantageous to have two line frequency generators as already
described, to wit pulse oscillator 6 and line oscillator 6' which is
present in the picture display device and which is directly synchronized
in known manner by line synchronizing pulses 7'. In fact, in this case
line oscillator 6' applies a signal of great amplitude and free from
interference to pulse oscillator 6. However, it is alternatively
possible to combine pulse oscillator 6 and line oscillator 6' in one
single oscillator 6" (see FIG. 1) which results in an economy of
components. It will be evident that line oscillator 6' and oscillator 6"
may alternatively be synchronized indirectly, for example, by means of
a phase discriminator. It is to be noted neither pulse oscillator 6,
line oscillator 6' and oscillator 6" nor modulator 5 can be fed by the
supply described since output voltage V o is still not
present when the mains voltage is switched on. Said circuit arrangements
must therefore be fed directly from the input terminals. If as
described above these circuit arrangements are to be separated from the
mains, a small separation transformer can be used whose primary winding
is connected between the mains voltage terminals and whose secondary
winding is connected to ground at one end and controls a rectifier at
the other end.
Capacitor 27 is arranged parallel to efficiency diode 7 so as to reduce the dissipation in switching transistor 2. In fact, if transistor 2 is switched off by the pulsatory control voltage, its collector current decreases and its collector-emitter voltage increases simultaneously so that the dissipated power is not negligible before the collector current has becomes zero. If efficiency diode 7 is shunted by capacitor 27 the increase of the collector-emitter voltage is delayed i.e., this voltage does not assume high values until the collector current has already been reduced. It is true that in that case the dissipation in transistor 2 slightly increases when it is switched on by the pulsatory control voltage but on the other hand since the current flowing through diode 7 has decreased due to the presence of the secondary windings, its inverse current is also reduced when transistor 2 is switched on and hence its dissipation has become smaller. In addition it is advantageous to delay these switching-on and switching-off periods to a slight extent because the switching pulses then contain fewer Fourier components of high frequency which may cause interferences in the picture display device and which may give rise to visible interferences on the screen of the display tube. These interferences occupy a fixed position on the displayed image because the switching frequency is the line frequency which is less disturbing to the viewer. In a practical circuit wherein the line frequency is 15,625 Hz and wherein switching transistor 2 is an experimental type suitable for a maximum of 350 V collector-emitter voltage or 1 A collector current and wherein efficiency diode 7 is of the Philips type BA 148 the capacitance of capacitor 27 is approximately 680 pF whilst the load is 70 W on the primary and 20 W on the secondary side of transformer 9. The collector dissipation upon switching off is 0.3 W (2.5 times smaller than without capacitor 27) and 0.7 W upon switching on.
As
is known the so-called pincushion distortion is produced in the
picture display tubes having a substantially flat screen and large
deflection angles which are currently used. This distortion is
especially a problem in color television wherein a raster correction
cannot be brought about by magnetic means. The correction of the
so-called East-West pincushion distortion i.e., in the horizontal
direction on the screen of the picture display tube can be established
in an elegant manner with the aid of the circuit arrangement according
to the invention. In fact, if the voltage generated by comparison
circuit 12 and being applied to modulator 5 for duration-modulating
pulsatory voltage 3 is modulated by a parabola voltage 28 of field
frequency, pulsatory voltage 3 is also modulated thereby. If the power
consumption of the line deflection circuit forms part of the load on
the output voltage of the chopper, the signal applied to the line
deflection coils is likewise modulated in the same manner. Conditions
therefore are that the parabola voltage 28 of field frequency has
a polarity such that the envelope of the sawtooth current of line
frequency flowing through the line deflection coils has a maximum in the
middle of the scan of the field period and that charge capacitor 10
has not too small an impedance for the field frequency. On the other
hand the other supply voltages which are generated by the circuit
arrangement according to the invention and which might be hampered by
this component of field frequency must be smoothed satisfactorily.
A practical embodiment of the described example with the reference numerals given provides an output for the supply of approximately 85 percent at a total load of 90 W, the internal resistance for direct current loads being 1.5 ohms and for pulsatorycurrents being
approximately 10 ohms. In case of a variation of ± 10 percent of the
mains voltage, output voltage V o is stable within 0.4 V.
Under the nominal circumstances the collector dissipation of switching
transistor 2 is approximately 2.5 W.
Since the internal resistance of the supply is so small, it can be used advantageously, for example, at terminal 15 for supplying a class-B audio amplifier which forms part of the display device. Such an amplifier has the known advantages that its dissipation is directly proportional to the amplitude of the sound to be reproduced and that its output is higher than that of a class-A amplifier. On the other hand a class-A amplifier consumes a substantially constant power so that the internal resistance of the supply voltage source is of little importance. However, if this source is highly resistive, the supply voltage is modulated in the case of a class-B amplifier by the audio information when the sound intensity is great which may detrimentally influence other parts of the display device. This drawback is prevented by means of the supply according to the invention.
The 50 Hz ripple voltage which is superimposed on the rectified input voltage V i is compensated by comparison circuit 12 and modulator 5 since this ripple voltage may be considered to be a variation of input voltage V i . A further compensation is obtained by applying a portion of this ripple voltage with suitable polarity to comparison circuit 12. It is then sufficient to have a lower value for the smoothing capacitor which forms part of rectifier circuit 1 (see FIG. 3). The parabola voltage 28 of field frequency originating from the field time base is applied to the same circuit 12 so as to correct the East-West pincushion distortion.
Such a circuit arrangement
is known from German "Auslegeschrift" 1.293.304. wherein a circuit
arrangement is described which has for its object to convert an input
direct voltage which is generated between two terminals into a
different direct voltage. The circuit employs a switch connected to the
first terminal of the input voltage and periodically opens and closes
so that the input voltage is converted into a pulsatory voltage. This
pulsatory voltage is then applied to a coil. A diode is arranged
between the junction of the switch and the coil and the second terminal
of the input voltage whilst a load and a charge capacitor in parallel
thereto are arranged between the other end of the coil and the second
terminal of the input voltage. The assembly operates in accordance with
the known efficiency principle i.e., the current supplied to the load
flows alternately through the switch and through the diode. The
function of the switch is performed by a switching transistor which is
driven by a periodical pulsatory voltage which saturates this
transistor for a given part of the period. Such a configuration is
known under different names in the literature; it will be referred to
herein as a "chopper." A known advantage thereof, is that the switching
transistor must be able to stand a high voltage or provide a great
current but it need not dissipate a great power. The output voltage of
the chopper is compared with a constant reference voltage. If the
output voltage attempts to vary because the input voltage and/or the
load varies, a voltage causing a duration modulation of the pulses is
produced at the output of the comparison arrangement. As a result the
quantity of the energy stored in the coil varies and the output voltage
is maintained constant. In the German "Auslegeschrift" referred to it
is therefore an object to provide a stabilized supply voltage device.In the circuit arrangement according to the mentioned German "Auslegeschrift" the frequency of the load variations or a harmonic thereof is chosen as the frequency for the switching voltage. Particularly when the load fed by the chopper is the line deflection circuit of a picture display device, wherein thus the impedance of the load varies in the rhythm of the line frequency, the frequency of the switching voltage is equal to or is a multiple of the line frequency.
It
is to be noted that the chopper need not necessarily be formed as that
in the mentioned German "Auslegeschrift." In fact, it is known from
literature that the efficiency diode and the coil may be exchanged. It
is alternatively possible for the coil to be provided at the first
terminal of the input voltage whilst the switching transistor is
arranged between the other end and the second terminal of the input
voltage. The efficiency diode is then provided between the junction of
said end and the switching transistor and the load. It may be recognized
that for all these modifications a voltage is present across the
connections of the coil which voltage has the same frequency and the
same shape as the pulsatory switching voltage. The control voltage of a
line deflection circuit is a pulsatory voltage which causes the line
output transistor to be saturates and cut off alternately. The invention
is based on the recognition that the voltage present across the
connections of the coil is suitable to function as such a control
voltage and that the coil constitutes the primary of a transformer. To
this end the circuit arrangement according to the invention is
characterized in that a secondary winding of the transformer
drives the switching element which applies a line deflection current
to line deflection coils and by which the voltage for the final anode
of a picture display tube which forms part of the picture display
device is generated, and that the ratio between the period during which
the switching transistor is saturated and the entire period, i.e., the
switching transistor duty cycle is between 0.3 and 0.7 during normal
operation.The invention is also based on the
recognition that the duration modulation which is necessary to
stabilize the supply voltage with the switching transistor does not
exert influence on the driving of the line output transistor. This
resides in the fact that in case of a longer or shorter cut-off period
of the line output transistor the current flowing through the line
deflection coils thereof is not influenced because of the efficiency
diode current and transistor current are taken over or, in case of a
special kind of transistor, the collector-emitter current is taken over
by the base collector current and conversely. However, in that case
the above-mentioned ratios of 0.3 : 0.7 should be taken into account
since otherwise this take-over principle is jeopardized.As will be further explained the use of the switching transistor as a driver for the line output transistor in an embodiment to be especially described hereinafter has the further advantage that the line output transistor automatically becomes non-conductive when this switching transistor is short circuited so that the deflection and the EHT for the display tube drop out and thus avoid damage thereof.
Due to the step according to the invention the switching transistor in the stabilized supply functions as a driver for the line deflection circuit. The circuit arrangement according to the invention may in addition be equipped with a very efficient safety circuit so that the reliability is considerably enhanced, which is described in the U.S. Pat. No. 3,629,686. The invention is furthermore based on the recognition of the fact that the pulsatory voltage present across the connections of the coil is furthermore used and to this end the circuit arrangement according to the invention is characterized in that secondary windings of the transformer drive diodes which conduct simultaneously with the efficiency diode so as to generate further stabilized direct voltages, one end of said diodes being connected to ground.
In order that the invention may be readily carried into effect, a few embodiments thereof will now be described in detail by way of example with reference to the accompanying diagrammatic drawings in which:
FIG. 1 shows a principle circuit diagram wherein the chopper and the line deflection circuit are further shown but other circuits are not further shown.
FIGS. 2a, 2b and 2c show the variation as a function of time of two currents and of a voltage occurring in the circuit arrangement according to FIG. 1.
FIGS. 3a 3b, 3c and 3d show other embodiments of the chopper.
FIGS. 4a and 4b show modifications of part of the circuit arrangement of FIG. 1.
In
FIG. 1 the reference numeral 1 denotes a rectifier circuit which
converts the mains voltage supplied thereto into a non-stabilized direct
voltage. The collector of a switching transistor 2 is connected to one
of the two terminals between which this direct voltage is obtained,
said transistor being of the npn-type in this embodiment and the base
of which receives a pulsatory voltage which originates through a
control stage 4 from a modulator 5 and causes transistor 2 to be
saturated and cut off alternately. The voltage waveform 3 is produced
at the emitter of transistor 2. In order to maintain the output voltage
of the circuit arrangement constant, the duration of the pulses
provided is varied in modulator 5. A pulse oscillator 6 supplies the
pulsatory voltage to modulator 5 and is synchronized by a signal of
line frequency which originates from the line oscillator 6' present in
the picture display device. This line oscillator 6' is in turn directly
synchronized in known manner by pulses 7' of line frequency which are
present in the device and originate for example from a received
television signal if the picture display device is a television
receiver. Pulse oscillator 6 thus generates a pulsatory voltage the
repetition frequency of which is the line frequency.
V o = V i . δ
Load 11 of the chopper consists in the consumption of parts of the picture display device which are fed by output volt
age V 0 .
In a practical embodiment of the circuit arrangement according to FIG.
1 wherein the mains alternating voltage has a nominal effective value
of 220 V and the rectified voltage V i is approximately 270 V, output voltage V o
for δ = 0.5 is approximately 135 V. This makes it also possible, for
example, to feed a line deflection circuit as is shown in FIG. 1 wherein
load 11 then represents different parts which are fed by the chopper.
Since voltage V o is maintained constant due to pulse
duration modulation, the supply voltage of this line deflection circuit
remains constant with the favorable result that the line amplitude(=
the width of the picture displayed on the screen of the picture display
tube) likewise remains constant as well as the EHT required for the
final anode of the picture display tube in the same circuit arrangement
independent of the variations in the mains voltage and the load on the
EHT generator (= variations in brightness).However,
variations in the line amplitude and the EHT may occur as a result of
an insufficiently small internal impedance of the EHT generator.
Compensation means are known for this purpose. A possibility within the
scope of the present invention is to use comparison circuit 12 for this
purpose. In fact, if the beam current passes through an element having
a substantially quadratic characteristic, for example, a
voltage-dependent resistor, then a variation for voltage V o
may be obtained through comparison circuit 12 which variation is
proportional to the root of the variation in the EHT which is a known
condition for the line amplitude to remain constant.In addition this facilitates smoothing of voltage V o since the repetition frequency of pulsatory voltage 3 is many times higher than that of the mains and a comparatively small value may be sufficient for charge capacitor 10. If charge capacitor 10 has a sufficiently high value for the line frequency, voltage V o is indeed a direct voltage so that a voltage having the same form as pulsatory voltage 3 is produced across the terminals of primary winding 8. Thus voltages which have the same shape as pulsatory voltage 3 but have a greater or smaller amplitude are produced across secondary windings 13, 14 of transformer 9 (FIG. 1 shows only 2 secondary windings but there may be more). The invention is based on the recognition that one end of each secondary winding is connected to earth while the other end thereof drives a diode, the winding sense of each winding and the direction of conductance of each diode being chosen to be such that these diodes conduct during the same period as does efficiency diode 7. After smoothing, stabilized supply voltages, for example, at terminal 15 are generated in this manner at the amplitudes and polarities required for the circuit arrangements present in the picture display device. In FIG. 1 the voltage generated at terminal 15 is, for example, positive relative to earth. It is to be noted that the load currents of the supply voltages obtained in this manner cause a reduction of the switching power which is economized by efficiency diode 7. The sum of all diode currents including that of diode 7 is in fact equal to the current which would flow through diode 7 if no secondary winding were wound on transformer 9 and if no simultaneous diode were used. This reduction may be considered an addit
ional
advantage of the circuit arrangement according to the invention, for a
diode suitable for smaller powers may then be used. However, it will be
evident that the overall secondary load must not exceed the primary
load since otherwise there is the risk of efficiency diode 7 being
blocked so that stabilization of the secondary supply voltages would be
out of the question.It is to be noted that a parabola voltage of line frequency as shown at 28 is produced across the charge capacitor 10 if this capacitor is given a smaller capacitance so that consequently the so-called S-correction is established.
In FIG. 1 charge capacitors are arranged between terminals 15 etc. and earth so as to ensure that the voltages on these points are stabilized direct voltages. If in addition the mean value of the voltage on one of these terminals has been made equal to the effective value of the alternating voltage which is required for heating the filament of the picture display tube present in the picture display device, this voltage is suitable for this heating. This is a further advantage of the invention since the cheap generation of a stabilized filament voltage for the picture display tube has always been a difficult problem in transistorized arrangements.
A further advantage of the picture display device according to the invention is that transformer 9 can function as a separation transformer so that the different secondary windings can be separated from the mains and their lower ends can be connected to ground of the picture display device. The latter step makes it possible to connect a different apparatus such as, for example, a magnetic recording and/or playback apparatus to the picture display device without earth connection problems occurring.
In FIG. 1 the reference numeral 14 denotes a secondary winding of transformer 9 which in accordance with the previously mentioned recognition of the invention can drive line output transistor 16 of the line deflection circuit 17. Line deflection circuit 17 which is shown in a simplified form in FIG. 1 includes inter alia line deflection coils 18 and an EHT transformer 19 a secondary winding 20 of which serves for generating the EHT required for the acceleration anode of the picture display tube. Line deflection circuit 17 is fed by the output voltage V o of the chopper which voltage is stabilized due to the pulse duration modulation with all previously mentioned advantages. Line deflection circuit 17 corresponds, for example, to similar arrangements which have been described in U.S. Pat. No. 3,504,224 issued Mar. 31, 1970 to J.J. Reichgelt et al., U.S. patent application Ser. No. 737,009 filed June 14, 1968 by W. H. Hetterscheid and U.S. application Ser. No. 26,497 filed April 8, 1970 by W. Hetterscheid et al. It will be evident that differently formed lined deflection circuits are alternatively possible.
It will now be shown that secondary winding 14 can indeed drive a line deflection circuit so that switching transistor 2 can function as a driver for the line deflection. FIGS. 2a and b show the variation as a function of time of the current i C which flows in the collector of transistor 16 and of the drive voltage v 14 across the terminals of secondary winding 14. During the flyback period (0, t 1 ) transistor 16 must be fully cut off because a high voltage peak is then produced at its collector; voltage v 14 must then be absolutely negative. During the scan period (t 1 , t 4 ) a sawtooth current i C flows through the collector electrode of transistor 16 which current is first negative and then changes its direction. As the circuit arrangement is not free from loss, the instant t 3 when current i C becomes zero lies, as is known, before the middle of the scan period. At the end t 4 of the scan period transistor 16 must be switched off again. However, since transistor 16 is saturated during the scan period and since this transistor must be suitable for high voltages and great powers so that its collector layer is thick, this transistor has a very great excess of charge carriers in both its base and collector layers. The removal of these charge carriers takes a period t s which is not negligible whereafter the transistor is indeed switched off. Thus the fraction δ T of the line period T at which v 14 is positive must end at the latest at the instant (t 4 - t s ) located after the commencement (t = 0) of the previous flyback.
The time δ T may be initiated at any instant t 2 which is located between the end t 1 of the flyback period and the instant t 3 when collector current i C reverses its direction. It is true that emitter current flows through transistor 16 at the instant t 2 , but collector current i C is not influenced thereby, at least not when the supply voltage (= V o ) for line deflection circuit 17 is high enough. All this has been described in the U.S. Pat. No. 3,504,224. The same applies to line deflection circuits wherein the collector base diode does not function as an efficiency diode as is the case in the described circuit 17, but wherein an efficiency diode is arranged between collector and emitter of the line output transistor. In such a case the negative part of the current i C of FIG. 2a represents the current flowing through the said efficiency diode.
After the instant t 3 voltage v 14 must be positive. In other words, the minimum duration of the period T when voltage v 14 must be positive is (t 4 - t s ) - t 3 whilst the maximum duration thereof is (t 4 - t s ) - t 1 . In a television system employing 625 lines per raster the line period t 4 is approximately 64 μus and the flyback period is approximately 12 μus. Without losses in the circuit arrangement instant t 3 would be located approximately 26 μus after the instant t 1 , and with losses a reasonable value is 22 μus which is 34 μus after the commencement of the period. If for safety's sake it is assumed that t s lasts approximately 10 μus, the extreme values of δ T are approximately 20 and 42 μus and consequently the values for δ are approximately 0.31 and 0.66 at a mean value which is equal to approximately 0.49. It was previously stated that a mean value of δ = 0.5 was suitable. Line deflection circuit 17 can therefore indeed be used in combination with the chopper in the manner described, and the relative variation of δ may be (0.66 - 0.31) : 0.49 = 71.5 percent. This is more than necessary to obviate the variations in the mains voltage or in the various loads and to establish the East-West modulation and ripple compensation to be described hereinafter. In fact, if it is assumed that the mains voltage varies between -15 and +10 percent of the nominal value of 220 V, while the 50 Hz ripple voltage which is superimposed on the input voltage V i has a peak-to-peak value of 40 V and V i is nominally 270 V, then the lowest occurring V i is:
0.85 × 270 V - 20 V = 210 V and the highest occurring V i is
1.1 × 270 V + 20 V = 320 V. For an output voltage V o of 135 V the ratio must thus vary between
δ = 135 : 210 = 0.64 and δ = 135 : 320 = 0.42.
A considerable problem presenting itself is that of the simultaneous or non-simultaneous drive of line output transistor 16 with switching transistor 2, it being understood that in case of simultaneous drive both transistors are simultaneously bottomed, that is during the period δ T. This depends on the winding sense of secondary winding 14 relative to that of primary winding 8. In FIG. 1 it has been assumed that the drive takes place simultaneously so that the voltage present across winding 14 has the shape shown in FIG. 2b. This voltage assumes the value n(V i - V o ) in the period δ T and the value -nVo in the period (1 - δ )T, wherein n is the ratio of the number of turns on windings 14 and 8 and wherein V o is maintained constant at nominal mains voltage V o = δ V inom . However, if as a result of an increase or a decrease of the mains voltage V i increases or decreases proportionally therewith, i.e., V i = V i nom + Δ V, the positive portion of V 14 becomes equal to n(V i nom - V o +Δ V) = n [(1 -δ)V i nom +ΔV] = n(0.5 V inom +ΔV) if δ = 0.5 for V i = V i nom. Relatively, this is a variation which is twice as great. For example, if V i nom = 270 V and V o = 135 V, a variation in the mains voltage of from -15 to +10 percent causes a variation of V i of from -40.5 V to +27 V which ranges from -30 to +20 percent of 135 V which is present across winding 8 during the period δ T. The result is that transistor 16 can always be bottomed over a large range of variation. If the signal of FIG. 2b would be applied through a resistor to the base of transistor 16, the base current thereof would have to undergo the same variation while the transistor would already be saturated in case of too low a voltage. In this case it is assumed that transformer 9 is ideal (without loss) and that coil 21 has a small inductance as is explained in the U.S. patent application Ser. No. 737,009 above mentioned. It is therefore found to be desirable to limit the base current of transistor 16.
During switching off, t 2 ,
of transistor 16 coil 22 must exert no influence and coil 21 must
exert influence which is achieved by arranging a diode 23 parallel to
coil 22. Furthermore the control circuit of transistor 16 in this
example comprises the two diodes 24 and 25 as described in U.S.
application Ser. No. 26,497 above referred to, wherein one of these
diodes, diode 25 in FIG. 1, must be shunted by a resistor.
The control circuit of transistor 16 may alternatively be formed as is shown in FIG. 4. In fact, it is known that coil 21 may be replaced by the parallel arrangement of a diode 21' and a resistor 21" by which the inverse current can be limited. To separate the path of the inverse current from that of the forward current the parallel arrangement of a the diode 29' and a resistor 29" must then be present. This leads to the circuit arrangement shown in the upper part of FIG. 4. This circuit arrangement may now be simplified if it is noted that diodes 25 and 21' on the one hand and diodes 23 and 29' on the other hand are series-arranged. The result is shown in the lower part of FIG. 4 which, as compared with the circuit arrangement of FIG. 1, employs one coil less and an additional resistor.
FIG. 3 shows possible modifications of the chopper. FIG. 3a shown in a simplified form the circuit arrangement according to FIG. 1 wherein the pulsatory voltage present across the connections of windings 8 has a peak-to-peak amplitude of V i - V o = 0.5 V i for δ = 0.5, As has been stated, the provision of coil 22 gives a relative variation for the base current of transistor 16 which is equal to that of the mains voltage. In the cases according to FIG. 3b, 3c and 3d the peak-to-peak amplitude of the voltage across winding 8 is equal to V i so that the provision of coil 22 results in a relative variation which is equal to half that of the mains voltage which is still more favorable than in the first case.
Transistors
of the npn type are used in FIG. 3. If transistors of the pnp type are
used, the relevant efficiency diodes must of course be reversed.In this connection it is to be noted that it is possible to obtain an output voltage V o with the aid of the modifications according to FIGS. 3b, c and d, which voltage is higher than input voltage V i . These modifications may be used in countries such as, for example, the United of America or France where the nominal mains voltage is 117 or 110 V without having to modify the rest of the circuit arrangement.
The above-mentioned remark regarding the sum of the diode currents only applies, however, for the modifications shown in FIGS. 3a and d.
If line output transistor 16 is not simultaneously driven with switching transistor 2, efficiency diodes 7 conducts simultaneously with transistor 16 i.e., during the period which is denoted by δ T in FIGS. 1 and 2b. During that period the output voltage V o of the chopper is stabilized so that the base current of transistor 16 is stabilized without further difficulty. However, a considerable drawback occurs. In FIG. 1 the reference numeral 26 denotes a safety circuit the purpose of which is to safeguard switching transistor 2 when the current supplied to load 11 and/or line deflection circuit 17 becomes to high, which happens because the chopper stops. After a given period output voltage V o is built up again, but gradually which means that the ratio δ is initially small in the order of 0.1. All this is described in U.S. patent No. 3,629,686. The same phenomenon occurs when the display device is switched on. Since δ = 0.1 corresponds to approximately 6 μs when T = 64 μs, efficiency diode 7 conducts in that case for 64 - 6 = 58 μus so that transistor 16 is already switched on at the end of the scan or at a slightly greater ratio δ during the flyback. This would cause an inadmissibly high dissipation. For this reason the simultaneous drive is therefore to be preferred.
The line deflection circuit itself is also safeguarded: in fact, if something goes wrong in the supply, the driver voltage of the line deflection circuit drops out because the switching voltage across the terminals of primary winding 8 is no longer present so that the deflection stops. This particularly happens when switching transistor 2 starts to constitute a short-circuit between emitter and collector with the result that the supply voltage V o for the line deflection circuit in the case of FIG. 1 becomes higher, namely equal to V i . However, the line output transformer is now cut off and is therefore also safe as well as the picture display tube and other parts of the display device which are fed by terminal 15 or the like. However, this only applies to the circuit arrangement according to FIG. 1 or 3a.
Capacitor 27 is arranged parallel to efficiency diode 7 so as to reduce the dissipation in switching transistor 2. In fact, if transistor 2 is switched off by the pulsatory control voltage, its collector current decreases and its collector-emitter voltage increases simultaneously so that the dissipated power is not negligible before the collector current has becomes zero. If efficiency diode 7 is shunted by capacitor 27 the increase of the collector-emitter voltage is delayed i.e., this voltage does not assume high values until the collector current has already been reduced. It is true that in that case the dissipation in transistor 2 slightly increases when it is switched on by the pulsatory control voltage but on the other hand since the current flowing through diode 7 has decreased due to the presence of the secondary windings, its inverse current is also reduced when transistor 2 is switched on and hence its dissipation has become smaller. In addition it is advantageous to delay these switching-on and switching-off periods to a slight extent because the switching pulses then contain fewer Fourier components of high frequency which may cause interferences in the picture display device and which may give rise to visible interferences on the screen of the display tube. These interferences occupy a fixed position on the displayed image because the switching frequency is the line frequency which is less disturbing to the viewer. In a practical circuit wherein the line frequency is 15,625 Hz and wherein switching transistor 2 is an experimental type suitable for a maximum of 350 V collector-emitter voltage or 1 A collector current and wherein efficiency diode 7 is of the Philips type BA 148 the capacitance of capacitor 27 is approximately 680 pF whilst the load is 70 W on the primary and 20 W on the secondary side of transformer 9. The collector dissipation upon switching off is 0.3 W (2.5 times smaller than without capacitor 27) and 0.7 W upon switching on.
As
is known the so-called pincushion distortion is produced in the
picture display tubes having a substantially flat screen and large
deflection angles which are currently used. This distortion is
especially a problem in color television wherein a raster correction
cannot be brought about by magnetic means. The correction of the
so-called East-West pincushion distortion i.e., in the horizontal
direction on the screen of the picture display tube can be established
in an elegant manner with the aid of the circuit arrangement according
to the invention. In fact, if the voltage generated by comparison
circuit 12 and being applied to modulator 5 for duration-modulating
pulsatory voltage 3 is modulated by a parabola voltage 28 of field
frequency, pulsatory voltage 3 is also modulated thereby. If the power
consumption of the line deflection circuit forms part of the load on
the output voltage of the chopper, the signal applied to the line
deflection coils is likewise modulated in the same manner. Conditions
therefore are that the parabola voltage 28 of field frequency has
a polarity such that the envelope of the sawtooth current of line
frequency flowing through the line deflection coils has a maximum in the
middle of the scan of the field period and that charge capacitor 10
has not too small an impedance for the field frequency. On the other
hand the other supply voltages which are generated by the circuit
arrangement according to the invention and which might be hampered by
this component of field frequency must be smoothed satisfactorily.A practical embodiment of the described example with the reference numerals given provides an output for the supply of approximately 85 percent at a total load of 90 W, the internal resistance for direct current loads being 1.5 ohms and for pulsatory
currents being
approximately 10 ohms. In case of a variation of ± 10 percent of the
mains voltage, output voltage V o is stable within 0.4 V.
Under the nominal circumstances the collector dissipation of switching
transistor 2 is approximately 2.5 W.Since the internal resistance of the supply is so small, it can be used advantageously, for example, at terminal 15 for supplying a class-B audio amplifier which forms part of the display device. Such an amplifier has the known advantages that its dissipation is directly proportional to the amplitude of the sound to be reproduced and that its output is higher than that of a class-A amplifier. On the other hand a class-A amplifier consumes a substantially constant power so that the internal resistance of the supply voltage source is of little importance. However, if this source is highly resistive, the supply voltage is modulated in the case of a class-B amplifier by the audio information when the sound intensity is great which may detrimentally influence other parts of the display device. This drawback is prevented by means of the supply according to the invention.
The 50 Hz ripple voltage which is superimposed on the rectified input voltage V i is compensated by comparison circuit 12 and modulator 5 since this ripple voltage may be considered to be a variation of input voltage V i . A further compensation is obtained by applying a portion of this ripple voltage with suitable polarity to comparison circuit 12. It is then sufficient to have a lower value for the smoothing capacitor which forms part of rectifier circuit 1 (see FIG. 3). The parabola voltage 28 of field frequency originating from the field time base is applied to the same circuit 12 so as to correct the East-West pincushion distortion.
The PHILIPS TDA3560A
is a decoder for the PAL colour television standard. It combines all functions required for the identification
and demodulation of PAL signals. Furthermore it contains a luminance amplifier, an RGB-matrix and amplifier. These
amplifiers supply output signals up to 5 V peak-to-peak (picture information) enabling direct drive of the discrete output
stages. The circuit also contains separate inputs for data insertion, analogue as well as digital, which can be used for
text display systems (e.g. (Teletext/broadcast antiope), channel number display, etc. Additional to the TDA3560, the
circuit includes the following features:
· The peak white limiter is only active during the time that the 9,3 V level at the output is exceeded. The start of the
limiting function is delayed by one line period. This avoids peak white limiting by test patterns which have abrupt
transitions from colour to white signals.
· The brightness control is obtained by inserting a variable pulse in the luminance channel. Therefore the ratio of
brightness variation and signal amplitude at the three outputs will be identical and independent of the difference in gain
of the three channels. Thus discolouring due to adjustment of contrast and brightness is avoided.
· Improved suppression of the internal RGB signals when the device is switched to external signals, and vice versa.· Non-synchronized external RGB signals do not disturb the black level of the internal signals.
· Improved suppression of the residual 4,4 MHz signal in the RGB output stages.
· Cascoded stages in the demodulators and burst phase detector minimize the radiation of the colour demodulator
inputs.
· High current capability of the RGB outputs and the chrominance output.
APPLICATION INFORMATION
The function is described against the corresponding pin
number.
1. + 12 V power supply
The circuit gives good operation in a supply voltage range
between 8 and 13,2 V provided that the supply voltage for
the controls is equal to the supply voltage for the
TDA3561A. All signal and control levels have a linear
dependency on the supply voltage. The current taken by
the device at 12 V is typically 85 mA. It is linearly
dependent on the supply voltage.
2. Control voltage for identification
This pin requires a detection capacitor of about 330 nF for
correct operation. The voltages available under various
signal conditions are given in the specification.
3. Chrominance inputThe chroma signal must be a.c.-coupled to the input.
Its amplitude must be between 55 mV and 1100 mV
peak-to-peak (25 mV to 500 mV peak-to-peak burst
signal). All figures for the chroma signals are based on a
colour bar signal with 75% saturation, that is the
burst-to-chroma ratio of the input signal is 1 : 2,25.
4. Reference voltage A.C.C. detector
This pin must be decoupled by a capacitor of about 330
nF. The voltage at this pin is 4,9 V.
5. Control voltage A.C.C.
The A.C.C. is obtained by synchronous detection of the
burst signal followed by a peak detector. A good noise
immunity is obtained in this way and an increase of the
colour for weak input signals is prevented. The
recommended capacitor value at this pin is 2,2 mF.
6. Saturation control
The saturation control range is in excess of 50 dB.
The control voltage range is 2 to 4 V. Saturation control is
a linear function of the control voltage.
When the colour killer is active, the saturation control
voltage is reduced to a low level if the resistance of the
external saturation control network is sufficiently high.
Then the chroma amplifier supplies no signal to the
demodulator. Colour switch-on can be delayed by proper
choice of the time constant for the saturation control
setting circuit.
When the saturation control pin is connected to the power
supply the colour killer circuit is overruled so that the colour
signal is visible on the screen. In this way it is possible to
adjust the oscillator frequency without using a frequency
counter (see also pins 25 and 26).
7. Contrast controlThe contrast control range is 20 dB for a control voltage
change from + 2 to + 4 V. Contrast control is a linear
function of the control voltage. The output signal is
suppressed when the control voltage is 1 V or less. If one
or more output signals surpasses the level of 9 V the peak
white limiter circuit becomes active and reduces the output
signals via the contrast control by discharging C2 via an
internal current sink.
8. Sandcastle and field blanking input
The output signals are blanked if the amplitude of the input
pulse is between 2 and 6,5 V. The burst gate and clamping
circuits are activated if the input pulse exceeds a level of
7,5 V.
The higher part of the sandcastle pulse should start just
after the sync pulse to prevent clamping of video signal on
the sync pulse. The width should be about 4 ms for proper
A.C.C. operation.
9. Video-data switching
The insertion circuit is acti
vated by means of this input byan input pulse between 1 V and 2 V. In that condition, the
internal RGB signals are switched off and the inserted
signals are supplied to the output amplifiers. If only normal
operation is wanted this pin should be connected to the
negative supply. The switching times are very short
(< 20 ns) to avoid coloured edges of the inserted signals
on the screen.
10. Luminance signal input
The input signal should have a peak-to-peak amplitude of
0,45 V (peak white to sync) to obtain a black-white output
signal to 5 V at nominal contrast. It must be a.c.-coupled to
the input by a capacitor of about 22 nF. The signal is
clamped at the input to an internal reference voltage.
A 1 kW luminance delay line can be applied because the
luminance input impedance is made very high.
Consequently the charging and discharging currents of the
coupling capacitor are very small and do not influence the
signal level at the input noticeably. Additionally the
coupling capacitor value may be small.
PHILIPS 14CT3405 CAMPIGLI CHASSIS KT3 TRD Video signal processing circuit for a color television receiver PHILIPS TDA3560: In a video signal processing circuit for a color television receiver, a brightness setting, which is operative for external color signals as well as for internal color signals and which does not produce a color shift, can be obtained by combining with the luminance signal (Y) a level shift signal (H) the amplitude of which is adjustable by the brightness setting and by employing in each color channel two clamping circuits, the first one of which clamps a first reference level (RL1) in the external color signal (ER, EG, EB) onto a combination of the level shift signal and the internal color signal (R, G, B) and the second clamping circuit clamps a second reference leve (RL2) which occurs in the sum signal of the internal and the external color signal when the level shift signal has zero value, onto the cutoff level of the relevant electron gun of a picture display tube.
1. A video signal
processing circuit for a color television receiver having inputs for a
luminance signal, for color difference signals and for external color
signals, comprising respective matrix circuits for combining the
respective color difference signals with the luminance signal to form
respective color signals, respective first clamping circuits for
clamping the respective external color signals onto the respective color
signals, respective combining circuits for combining the respective
clamped external color signals with the respective color signals,
respective second clamping circuits for clamping the outputs of the
respective combining circuits onto a predetermined level, and a
brightness setting circuit, characterized in that the first clamping
circuits act on a first reference level in said respective external
color signals occurring in a first group of periods and the second
clamping circuits act on a second reference level occurring in a second
group of periods which differ from the periods of the first group, while
the brightness setting circuit is an amplitude setting circuit for a
level shift signal, which is combined with the luminance signal prior to
processing the color difference signals, with which the relative
position of the second reference level with respect to the remaining
portion of the luminance signal is adjustable. 2. A video signal processing circuit as claimed in claim 1, characterized in that the respective first and second clamping circuits are operative alternately and every other line flyback period.
Description:
BACKGROUND OF THE INVENTION
The invention relates to a video signal processing circuit for a color television receiver having inputs for a luminance signal, for color difference signals, and for external color signals, comprising a matrix circuit for combining a color difference signal with the luminance signal to form a color signal, a first clamping circuit for clamping an external color signal onto the corresponding color signal, a combining circuit for combining a clamped external color signal with the corresponding color signal, a second clamping circuit acting on an output signal of the combining circuit and a brightness setting circuit.
A video
signal processing circuit of the type defined above is described in
Philip Data Handbook for Integrated Circuits, Part 2, May, 1980 as IC
TDA3560. The brightness setting, which is common for internal and
external video signals, is obtained by means of a common direct current
level setting of the second clamping circuits. The settings of the three
electron guns of a picture display tube coupled to the outputs of the
video signal processing circuit are changed to an equal extent by this
direct current level setting as a result whereof, due to the mutual
differences in the efficiency of the phosphors of the picture display
tube, a color shift may occur at a brightness adjustment. It is an
object of the invention to prevent this.
SUMMARY OF THE INVENTION
According to the invention, a video signal processing circuit of the type defined in the preamble is therefore characterized in that the first clamping circuit acts on a first reference level occurring in a first group of periods and the second clamping circuit acts on a second reference level occurring in a second group of periods which differ from the periods of the first group, while the brightness setting circuit is an amplitude setting circuit for a level shift signal with which the relative position of the second reference level with respect to the remaining portion of the luminance signal is adjustable.
Owing to the measure in accordance with the invention, the common setting of the brightness for internal video signals is maintained and a color shift is prevented from occurring at a brightness setting.
DESCRIPTION OF THE DRAWINGS
An embodiment of the invention will now be further described by way of example with reference to the accompanying drawings.
In the drawings:
FIG. 1 illustrates, by means of a block schematic circuit diagram, a video signal processing circuit in accordance with the invention; and
FIG. 2 shows some waveforms such as they may occur in the circuit shown in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In
FIG. 1, an external red color signal ER' is applied to an input 1, a
red color difference signal (R-Y) to an input 3, an external green color
signal EG' to an input 5, a luminance signal Y to an input 7, a green
color difference signal (G-Y) to an input 9, an external blue color
signal EB' to an input 11, a blue color difference signal (B-Y) to an
input 13 and a synchronizing signal S to an input 15.
The luminance signal at the input 7 is shown in FIG. 2 as a waveform 207. In the line flyback periods this luminance signal has a black level Z which, for simplicity, is assumed to occur in all cases during the whole line flyback period but which may, of course, alternatively occur during only a portion of that line flyback period.
The luminance signal Y is applied to an input 17 of a combining circuit 19. To a further input 21 thereof, a level shift signal H is applied which, via an amplitude setting circuit 23, is obtained from an output 25 of a pulse generator 27, to an input 29 of which the synchronizing signal S is applied.
The level shift signal H is shown in FIG. 2 as a waveform 221 which in this case has a zero amplitude every other line flyback period and at other times an amplitude which depends on the setting of the amplitude setting circuit 23.
The respective color
difference signals (R-Y), (G-Y) and (B-Y) at the respective inputs 3, 9
and 13, are applied to inputs 31, 33 and 35, respectively, of matrix
circuits 37, 39 and 41, respectively, to respective inputs 43, 45 and 47
of which the combination Y+H of the luminance signal (Y) and the level
shift signal (H) is applied, and from respective outputs 49, 51 and 53,
the red (R) and green (G) and blue (B) color signals are obtained. FIG. 2
shows the red color signal of said color signals as a waveform 249.
The respective external color signals ER', EG' and EB' at the respective inputs 1, 5 and 11 are applied to respective inputs 61, 63 and 65 of respective combining circuits 67, 69 and 71 via respective capacitors 55, 57 and 59. Further inputs 73, 75 and 77, respectively, of the combining circuits 67, 69 and 71, respectively, are connected to the outputs 49, 51 and 53, respectively, of the matrix circuits 37, 39 and 41, respectively, and receive the red, green and blue color signals, respectively.
Arranged between the inputs 61 and 73, 63 and 75, and 65 and 77, respectively, there are first clamping circuits 79, 81 and 83, respectively, which, under the control of a pulse signal K1 coming from an output 84 of the pulse generator 27, clamps a first reference level RL1 in the respective external color signals ER', EG' and EB' onto the respective color signals R, G and B, as a result of which the respective clamped external color signals ER, EG and EB at the respective inputs 61, 63 and 65 of the combining circuits 67, 69 and 71 are produced, the signal level ER at the input 61 of the combining circuit 67 being shown in FIG. 2 as the waveform 261. The pulse signal K1 is shown in FIG. 2 as the waveform 284.
At respective outputs 85, 87 and 89 of the combining circuits 67, 69 and 71, respectively, there are now produced signals which are the sums of the respective clamped external color signals ER, EG and EB and the respective color signals R, G and B. Via respective capacitors 91, 93 and 95, said sum signals (ER+R), (EG+G) and (EB+B), respectively, are applied to respective inputs 97, 99 and 100 of respective video output amplifiers 102, 104 and 106, respective outputs 108, 110 and 112 of which being connected to respective cathodes of a picture display tube 114.
Second clamping circuits 116, 118 and 120, respectively, which are rendered operative by a pulse signal K2 coming from an output 122 of the pulse generator 27 and whereby a second reference level RL2 in the signals at the respective inputs 97, 99 and 100 is adjusted to a fixed potential, zero potential here, are connected to the respective inputs 97, 99 and 100 of the respective video output amplifiers 102, 104 and 106. This is shown in FIG. 2 by means of the waveform 297 for the signal (ER+R) at the input 97 of the video output amplifier 102. For the sake of clearness, the luminance signal (Y) and the red color difference signal (R-Y) are assumed to have zero values.
The picture display tube 114 has a deflection circuit 124 which is controlled by signals coming from outputs 126 and 128, respectively, of the pulse generator 27.
On the basis of FIG. 2, it will now be demonstrated that the brightness of the color signals as well as of the external color signals is adjustable by means of the amplitude setting circuit 23, more specifically in such a ratio, occurring at the picture display tube 114, that no color shift is produced.
If a luminance signal Y and a color difference signal
(R-Y) are produced and the external color signal ER' has zero value, the
signal at the output 49 of the matrix circuit 37 has the waveform 249
and likewise the signal at the input 97 of the video output amplifier
108, as during the occurrence of the signal K2 (waveform 222), the
second clamping circuit 116 has adjusted the second reference level RL2
to zero, which corresponds to the cutoff level of the relevant cathode
of the picture display tube 114. Outside the periods in which signal is
clamped to the second reference level RL2, the black level,
shown in the waveform 249 by means of a dashed line, of the color signal
at the input 97 of the video amplifier is determined by the amplitude
of the level shift signal H, which, in response to the video output
amplifier gain factors which are adapted to the efficiencies of the
phosphors of the picture display tube, are applied in the relevant
signal paths to the cathodes of the picture display tube 114 to said
cathodes in such an amplitude ratio that no color shift can be produced.
If there is an external color signal but no luminance and color
difference signals (Y=O, R-Y=O, G-Y=O, B-Y=O), then a signal is produced
at the input 97 of the video output amplifier 102 which has the
waveform 297 and which, during the occurrence of the second reference
level RL2, is clamped onto zero by the second clamping
circuit 116 by means of the clamping pulses K2 and which consequently
corresponds to the cutoff level of the relevant cathode of the picture
display tube 114. During the occurrence of the first reference level RL1
in the signal ER', the first clamping circuit 79 clamps the signal ER
(waveform 261) at the input 61 of the combining circit 61 onto the
output signal of the matrix circuit 37 during the occurrence of the
clamping pulses K1 (waveform 284). Now this output signal has the
waveform 221, as R-Y and Y have zero values. From the waveform 297, it
now appears that the signal ER+R, which in this case is equal to ER+H,
has, outside the periods in which the second reference level RL2
occurs in the waveform 297, a black level which is indicated by means
of a dashed line and is determined by the amplitude of the level shift
signal H. Also now this amplitude is applied in the proper ratio to the
cathodes of the picture display tube 114 by the video output amplifier
gain factors which are adapted to the efficiencies of the phosphors of
the picture display tube 114, so that no color shift can be produced.
It will be obvious that it is not imperative that the clamping pulses K1 and K2 be produced alternately and every other line flyback period. If so desired, the clamping pulses K1 may, for example, occur in a number of line trace periods of the field trace which are located outside the visible picture plane, and the clamping pulses K2 may occur in the line flyback periods. The clamping pulses K2 must be produced in the period in which the level shift signal causes the second reference level RL2 and the clamping pulses K1 outside said periods and in the periods the first level reference level RL1 occurs.
In the above-described embodiment the clamping circuits are provided in the form of short-circuiting switches which are arranged subsequent to capacitors which have for their function to block direct current signals. It will be obvious, that, if so desired, clamping circuits in the form of control circuits may alternatively be used and that in that event, if so desired, blocking the direct current component by a capacitor may be omitted.
If so desired, instead of an adder circuit 19, an insertion circuit may be employed by means of which, in the appropriate periods of the luminance signal, when the signal K2 is produced the reference level Z then present, is replaced by a new level which is influencable by the brightness setting .
The invention relates to a video signal processing circuit for a color television receiver having inputs for a luminance signal, for color difference signals, and for external color signals, comprising a matrix circuit for combining a color difference signal with the luminance signal to form a color signal, a first clamping circuit for clamping an external color signal onto the corresponding color signal, a combining circuit for combining a clamped external color signal with the corresponding color signal, a second clamping circuit acting on an output signal of the combining circuit and a brightness setting circuit.
A video
signal processing circuit of the type defined above is described in
Philip Data Handbook for Integrated Circuits, Part 2, May, 1980 as IC
TDA3560. The brightness setting, which is common for internal and
external video signals, is obtained by means of a common direct current
level setting of the second clamping circuits. The settings of the three
electron guns of a picture display tube coupled to the outputs of the
video signal processing circuit are changed to an equal extent by this
direct current level setting as a result whereof, due to the mutual
differences in the efficiency of the phosphors of the picture display
tube, a color shift may occur at a brightness adjustment. It is an
object of the invention to prevent this. SUMMARY OF THE INVENTION
According to the invention, a video signal processing circuit of the type defined in the preamble is therefore characterized in that the first clamping circuit acts on a first reference level occurring in a first group of periods and the second clamping circuit acts on a second reference level occurring in a second group of periods which differ from the periods of the first group, while the brightness setting circuit is an amplitude setting circuit for a level shift signal with which the relative position of the second reference level with respect to the remaining portion of the luminance signal is adjustable.
Owing to the measure in accordance with the invention, the common setting of the brightness for internal video signals is maintained and a color shift is prevented from occurring at a brightness setting.
DESCRIPTION OF THE DRAWINGS
An embodiment of the invention will now be further described by way of example with reference to the accompanying drawings.
In the drawings:
FIG. 1 illustrates, by means of a block schematic circuit diagram, a video signal processing circuit in accordance with the invention; and
FIG. 2 shows some waveforms such as they may occur in the circuit shown in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In
FIG. 1, an external red color signal ER' is applied to an input 1, a
red color difference signal (R-Y) to an input 3, an external green color
signal EG' to an input 5, a luminance signal Y to an input 7, a green
color difference signal (G-Y) to an input 9, an external blue color
signal EB' to an input 11, a blue color difference signal (B-Y) to an
input 13 and a synchronizing signal S to an input 15. The luminance signal at the input 7 is shown in FIG. 2 as a waveform 207. In the line flyback periods this luminance signal has a black level Z which, for simplicity, is assumed to occur in all cases during the whole line flyback period but which may, of course, alternatively occur during only a portion of that line flyback period.
The luminance signal Y is applied to an input 17 of a combining circuit 19. To a further input 21 thereof, a level shift signal H is applied which, via an amplitude setting circuit 23, is obtained from an output 25 of a pulse generator 27, to an input 29 of which the synchronizing signal S is applied.
The level shift signal H is shown in FIG. 2 as a waveform 221 which in this case has a zero amplitude every other line flyback period and at other times an amplitude which depends on the setting of the amplitude setting circuit 23.
The respective color
difference signals (R-Y), (G-Y) and (B-Y) at the respective inputs 3, 9
and 13, are applied to inputs 31, 33 and 35, respectively, of matrix
circuits 37, 39 and 41, respectively, to respective inputs 43, 45 and 47
of which the combination Y+H of the luminance signal (Y) and the level
shift signal (H) is applied, and from respective outputs 49, 51 and 53,
the red (R) and green (G) and blue (B) color signals are obtained. FIG. 2
shows the red color signal of said color signals as a waveform 249. The respective external color signals ER', EG' and EB' at the respective inputs 1, 5 and 11 are applied to respective inputs 61, 63 and 65 of respective combining circuits 67, 69 and 71 via respective capacitors 55, 57 and 59. Further inputs 73, 75 and 77, respectively, of the combining circuits 67, 69 and 71, respectively, are connected to the outputs 49, 51 and 53, respectively, of the matrix circuits 37, 39 and 41, respectively, and receive the red, green and blue color signals, respectively.
Arranged between the inputs 61 and 73, 63 and 75, and 65 and 77, respectively, there are first clamping circuits 79, 81 and 83, respectively, which, under the control of a pulse signal K1 coming from an output 84 of the pulse generator 27, clamps a first reference level RL1 in the respective external color signals ER', EG' and EB' onto the respective color signals R, G and B, as a result of which the respective clamped external color signals ER, EG and EB at the respective inputs 61, 63 and 65 of the combining circuits 67, 69 and 71 are produced, the signal level ER at the input 61 of the combining circuit 67 being shown in FIG. 2 as the waveform 261. The pulse signal K1 is shown in FIG. 2 as the waveform 284.
At respective outputs 85, 87 and 89 of the combining circuits 67, 69 and 71, respectively, there are now produced signals which are the sums of the respective clamped external color signals ER, EG and EB and the respective color signals R, G and B. Via respective capacitors 91, 93 and 95, said sum signals (ER+R), (EG+G) and (EB+B), respectively, are applied to respective inputs 97, 99 and 100 of respective video output amplifiers 102, 104 and 106, respective outputs 108, 110 and 112 of which being connected to respective cathodes of a picture display tube 114.
Second clamping circuits 116, 118 and 120, respectively, which are rendered operative by a pulse signal K2 coming from an output 122 of the pulse generator 27 and whereby a second reference level RL2 in the signals at the respective inputs 97, 99 and 100 is adjusted to a fixed potential, zero potential here, are connected to the respective inputs 97, 99 and 100 of the respective video output amplifiers 102, 104 and 106. This is shown in FIG. 2 by means of the waveform 297 for the signal (ER+R) at the input 97 of the video output amplifier 102. For the sake of clearness, the luminance signal (Y) and the red color difference signal (R-Y) are assumed to have zero values.
The picture display tube 114 has a deflection circuit 124 which is controlled by signals coming from outputs 126 and 128, respectively, of the pulse generator 27.
On the basis of FIG. 2, it will now be demonstrated that the brightness of the color signals as well as of the external color signals is adjustable by means of the amplitude setting circuit 23, more specifically in such a ratio, occurring at the picture display tube 114, that no color shift is produced.
If a luminance signal Y and a color difference signal
(R-Y) are produced and the external color signal ER' has zero value, the
signal at the output 49 of the matrix circuit 37 has the waveform 249
and likewise the signal at the input 97 of the video output amplifier
108, as during the occurrence of the signal K2 (waveform 222), the
second clamping circuit 116 has adjusted the second reference level RL2
to zero, which corresponds to the cutoff level of the relevant cathode
of the picture display tube 114. Outside the periods in which signal is
clamped to the second reference level RL2, the black level,
shown in the waveform 249 by means of a dashed line, of the color signal
at the input 97 of the video amplifier is determined by the amplitude
of the level shift signal H, which, in response to the video output
amplifier gain factors which are adapted to the efficiencies of the
phosphors of the picture display tube, are applied in the relevant
signal paths to the cathodes of the picture display tube 114 to said
cathodes in such an amplitude ratio that no color shift can be produced.
If there is an external color signal but no luminance and color
difference signals (Y=O, R-Y=O, G-Y=O, B-Y=O), then a signal is produced
at the input 97 of the video output amplifier 102 which has the
waveform 297 and which, during the occurrence of the second reference
level RL2, is clamped onto zero by the second clamping
circuit 116 by means of the clamping pulses K2 and which consequently
corresponds to the cutoff level of the relevant cathode of the picture
display tube 114. During the occurrence of the first reference level RL1
in the signal ER', the first clamping circuit 79 clamps the signal ER
(waveform 261) at the input 61 of the combining circit 61 onto the
output signal of the matrix circuit 37 during the occurrence of the
clamping pulses K1 (waveform 284). Now this output signal has the
waveform 221, as R-Y and Y have zero values. From the waveform 297, it
now appears that the signal ER+R, which in this case is equal to ER+H,
has, outside the periods in which the second reference level RL2
occurs in the waveform 297, a black level which is indicated by means
of a dashed line and is determined by the amplitude of the level shift
signal H. Also now this amplitude is applied in the proper ratio to the
cathodes of the picture display tube 114 by the video output amplifier
gain factors which are adapted to the efficiencies of the phosphors of
the picture display tube 114, so that no color shift can be produced. 
It will be obvious that it is not imperative that the clamping pulses K1 and K2 be produced alternately and every other line flyback period. If so desired, the clamping pulses K1 may, for example, occur in a number of line trace periods of the field trace which are located outside the visible picture plane, and the clamping pulses K2 may occur in the line flyback periods. The clamping pulses K2 must be produced in the period in which the level shift signal causes the second reference level RL2 and the clamping pulses K1 outside said periods and in the periods the first level reference level RL1 occurs.
In the above-described embodiment the clamping circuits are provided in the form of short-circuiting switches which are arranged subsequent to capacitors which have for their function to block direct current signals. It will be obvious, that, if so desired, clamping circuits in the form of control circuits may alternatively be used and that in that event, if so desired, blocking the direct current component by a capacitor may be omitted.
If so desired, instead of an adder circuit 19, an insertion circuit may be employed by means of which, in the appropriate periods of the luminance signal, when the signal K2 is produced the reference level Z then present, is replaced by a new level which is influencable by the brightness setting .
BU208(A)
Silicon NPN
npn transistors,pnp transistors,transistors
Category: NPN Transistor, Transistor
MHz: <1 MHz
Amps: 5A
Volts: 1500V
HIGH VOLTAGE CAPABILITY
JEDEC TO-3 METAL CASE.
DESCRIPTION
The BU208A, BU508A and BU508AFI are
manufactured using Multiepitaxial Mesa
technology for cost-effective high performance
and use a Hollow Emitter structure to enhance
switching speeds.
APPLICATIONS:
* HORIZONTAL DEFLECTION FOR COLOUR TV With 110° or even 90° degree of deflection angle.
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
VCES Collector-Emit ter Voltage (VBE = 0) 1500 V
VCEO Collector-Emit ter Voltage (IB = 0) 700 V
VEBO Emitter-Base Voltage (IC = 0) 10 V
IC Collector Current 8 A
ICM Collector Peak Current (tp < 5 ms) 15 A
TO - 3 TO - 218 ISOWATT218
Ptot Total Dissipation at Tc = 25 oC 150 125 50 W
Tstg Storage Temperature -65 to 175 -65 to 150 -65 to 150 oC
Tj Max. Operating Junction Temperature 175 150 150 °C
PHILIPS TDA2611A 5 W audio power amplifier:
The TDA2611A is a monolithic integrated circuit in a 9-lead single in-line (SIL) plastic package with a high supply voltageaudio amplifier. Special features are:
• possibility for increasing the input impedance
• single in-line (SIL) construction for easy mounting
• very suitable for application in mains-fed apparatus
• extremely low number of external components
• thermal protection
• well defined open loop gain circuitry with simple quiescent current setting and fixed integrated closed loop gain.
PHILIPS TDA2581 CONTROL CIRCUIT FOR SMPS
The TDA2581 is a monolithic integrated circuit for controlling switched-mode power supplies (SMPS) which are provided with the drive for the horizontal deflection stage.
The circuit features the following:
— Voltage controlled horizontal oscillator.
— Phase detector.
— Duty factor control for the positive-going transient of the output signal.
— Duty factor increases from zero to its normal operation value.
— Adjustable maximum duty factor.
- Over-voltage and over-current protection with automatic re-start after switch-off.
— Counting circuit for permanent switch-off when n~times over~current or over-voltage is sensed
-Protection for open-reference voltage.
- Protection for too low supply voltage.
Protection against loop faults.
reference voltage minus 1,5 V.
TDA2541 IF AMPLIFIER WITH DEMODULATOR AND AFC
DESCRIPTION
The TDA2540 and 2541 are IF amplifier and A.M.
demodulator circuits for colour and black and white
television receiversusingPNPorNPNtuners. They
are intended for reception of negative or positive
modulation CCIR standard.
They incorporate the following functions : .Gain controlled amplifier .Synchronous demodulator .White spot inverter .Video preamplifier with noise protection .Switchable AFC .AGC with noise gating .Tuner AGC output (NPN tuner for 2540)-(PNP
tuner for 2541) .VCR switch for video output inhibition (VCR
play back).
The left positioned board contains all search tuning functions and it's based on potentiometers and digital selectors for each program change obtainable even via remote.
The board contains even additional complex fun
cions realized via discrete
components such analog functions - stby startup via remote -
search.PHILIPS 14CT3405 CAMPIGLI CHASSIS KT3 TRD Channel selector having a plurality of tuning systems:A channel selector characterized in that a plurality of receivers capable of simultaneously performing a receiving operation have a main part of a phase
-locked
loop frequency synthesizer connected in common thereto, the frequency
synthesizer having a programmable frequency divider, a phase
comparator, a reference oscillator and a reference frequency divider.
The frequency synthesizer is controlled so that a local oscillation
frequency corresponding to a determined frequency close to a broadcast
signal of a desired receiving channel is synthesized, and one of a
plurality of search tuning systems searches and tunes the broadcast
signal from the local oscillation frequency. 1. A channel selector for controlling the tuning frequency of a plurality of receivers capable of simultaneously performing receiving operations, each of said plurality of receivers having a portion of a phase-locked loop frequency synthesizer; wherein another portion of a phase-locked loop frequency synthesizer is commonly used by said portions of said synthesizers whereby each of said plurality of receivers has an equivalent complete phase-locked loop frequency synthesizer;
and wherein each of said plurality of receivers has its own low pass filter included in its equivalent phase-locked loop frequency synthesizer, and an output of a phase comparator is switched to an input terminal of one low pass filter from among said plurality of low pass filters by a 3-st
ate switching circuit.2. A channel selector according to claim 1, wherein said common portion of each of said equivalent phase-locked loop frequency synthesizers comprises a programmable frequency divider, a phase comparator, a reference oscillator and a reference frequency divider.
3. A channel selector according to claim 1, wherein said common portion of each of said equivalent phase-locked loop frequency synthesizers comprises a prescaler.
4. A channel selector according to claim 1, wherein said common portion of each of said equivalent phase-locked loop frequency synthesizers comprises a channel entry means and a code converter means.
5.
A channel selector for controlling the tuning frequency of a
plurality of receivers capable of simultaneously performing receiving
operations, each of said plurality of receivers having a portion of a
phase-locked loop frequency synthesizer; wherein another portion of a
phase-locked loop frequency synthesizer is commonly used by said
portions of said synthesizers whereby each of said plurality of
receivers has an equivalent complete phase-locked loop frequency
synthesizer; 
and wherein each of said equivalent phase-locked loop frequency synthesizers is controlled so that a local oscillation frequency corresponding to a predetermined frequency close to a broadcast signal of a desired receiving channel is synthesized, and one of a plurality of search tuning systems searches and tunes said broadcast signal from said local oscillation frequency whereby said broadcast signal of said desired receiving channel is tuned.
6. A channel selector for controlling the tuning frequency of a plurality of receivers capable of simultaneously performing receiving operations, each of said plurality of receivers having a portion of a phase-locked loop frequency synthesizer; wherein another portion of a phase-locked loop frequency synthesizer is commonly used by said portions of said synthesizers whereby each of said plurality of receivers has an equivalent complete phase-locked loop frequency synthesizer;
and wherein each of said phase-locked loop frequency synthesizers selects a desired receiving channel, and wherein a tuning voltage of said desired receiving channel is stored in a voltage memory means, and wherein said channel selector further comprises a tuning means provided for each of said plurality of receivers so that while receiving, said tuning means tunes in accordance with the output of said voltage memory means.
7.
A channel selector according to claims 5 or 6, wherein said common
portion of each of said equivalent phase-locked loop frequency
synthesizers comprises a programmable frequency divider, a phase
comparator, a reference oscillator and a reference frequency divider.
8. A channel selector according to claims 5 or 6, wherein said common portion of each of said equivalent phase-locked loop frequency synthesizers comprises a prescaler.
9. A channel selector according to claims 5 or 6, wherein said common portion of each of said equivalent phase-locked loop frequency synthesizers comprises a channel entry means and a code converter means.
Description:
BACKGROUND OF THE INVENTIONThis invention relates to a channel selector for use in television receivers, FM (frequency modulation) radio receivers, AM (amplitude modulation) radio receivers and so on.
PHILIPS SAB3034 COMPUTER INTERFACE FOR TUNING AND CONTROL (CITAC)
GENERAL DESCRIPTION
The SAB3034 provides closed-loop digital tuning of TV receivers, with or without a.f.c., as required. lt
tuner band selection.
The IC is used in conjunction with a microcomputer from the MAB84OO family and is controlled via a two-wire, bidirectional I2 C bus.
Featu res
Combined analogue and digital circuitry minimizes the number of additional interfacing components
required
Frequency measurement with resolution of 50 KHz
Selectable prescaler divisor of 64 or 256
32 V tuning voltage amplifier
4 high-current outputs for direct band selection
8 static digital to analogue converters (DACSI for control of analogue functions
Four general purpose input/output (l/O) ports
Tuning with control of speed and direction
Tuning with or without a.f.c.
Single-pin, 4 MHZ on-chip oscillator
I2 C bus slave transceiver
FUNCTIONAL DESCRIPTION
The SAB3034 is a monolithic computer interface which provides tuning and control functions and
operates in conjunction with a microcomputer via an I2 C bus.
Tuning
This is performed using frequency-locked loop digital control. Data corresponding to the required tuner
frequency is stored in a 15-bit frequency buffer. The actual tuner frequency, divided by a factor of 256
(or by 64) by a prescaler, is applied via a gate to a 15-bit frequency counter. This input (FDIV) is
measured over a period controlled by a time reference counter and is compared with the contents of the frequency buffer. The result of the comparison is used to control the tuning voltage so that the tuner frequency equals the contents of the frequency buffer multiplied by 50 kHz within a programmable tuning window (TUW).
The system cycles over a period of 6,4 ms (or 2,56 ms), controlled by the time reference counter which is clocked by an on-chip 4 lVlHz reference oscillator. Regulation of the tuning voltage is performed by a charge pump frequency-locked loop system. The charge IT flowing into the tuning voltage amplifier is controlled by the tuning counter, 3-bit DAC and the charge pump circuit. The charge IT is linear with the frequency deviation Af in steps of 50
NEC D8049AH
8-Bit Microcontroller-Microcomputer - Over 96 instructions, all 1-2 cycles
Intel
8-Bit Microcontrollers
Clock Frequency - Max. (Hz)=11.0M
Clock Frequency - Min. (Hz)=1.0M
Min Instruction Length (bits)=8
Max Instruction Length (bits)=16
Memory Addressing Range=64k
Number of Addressing Modes=5
On-Chip RAM (Bytes)=128
On-Chip ROM (bytes)=2k
Number of Interrupt Lines=1
No. of Non-Maskable Interrupts=0
Number of Maskable Interrupts=1
Number of I/O Lines=16
No. of I/O Ports=2
Vsup Nom.(V) Supply Voltage=5.0
Package=DIP
Pins=40
Military=N
Technology=NMOS
PHILIPS TDA3571 SYNC COMBINATION WITH TRANSMITTER IDENTIFICATION
AND VERTICAL 625 DIVIDER SYSTEMGENERAL DESCRIPTION
The TDA3571 B is a monolithic integrated circuit for use in colour television receivers with switched-
mode driven or self-regulating horizontal time-base circuits. It is designed in combination with the
TDA2581 to operate as a matched pair. When supplied with a composite video signal the TDA3571 B
delivers drive pulses for the TDA2581 and sync pulses for the vertical deflection. The circuit is
optimized for a horizontal and vertical frequency ratio of 625. It incorporates the following features:
Features
O Horizontal sync separator (including noise inverter) I
O Horizontal phase detector
0 Horizontal oscillator (31,25 kHz)
0 Sandcastle pulse generator
O Vertical sync pulse separator
O Very stable automatic vertical synchronization due to the 625 divider system, without delay after
channel change
I Three voltage level sensor on coincidence detector circuit output
I Video transmitter identification circuit for sound muting and search tuning systems
O Inhibit of vertical sync pulse when no video transmitter is detected
QUICK REFERENCE DATA
Supply voltage _
horizontal (pin 14) V14_13 typ. 12 V
vertical (pin 18) V13_13 typ. 12 V
Supply current (pin 14 + pin 18) V14+18 typ. 52 mA
Sync separator
input voltage level (peak-to-peak value) V2.131p.p) 0,07 to I V
slicing level typ. 50 % _
Output pulse E
horizontal (peak-to-peak value) V3_131p_p1 min. 10 V =
vertical sync (peak-to-peak value) V1_131p_p1 min. 10 V —
burst key (peak-to~peak value) V15_131p_p1 min. 10 V
Video transmitter identification circuit
Output voltage (pin 10)
sync pulse present V10_13 typ. 8 V
no sync pulse V1Q_13 max. 1 V
Phase locked loop
control sensitivity typ. 2000 Hz/;1s
holding range Af typ. 1 1000 Hz
catching range Af typ. : 900 Hz
Operating ambient temperature range Tamb -25 to + 65 °C
PACKAGE OUTLINE
18-lead DIL; plastic (SOT-102A).
FUNCTIONAL DESCRIPTION TDA3571
The video input voltage to drive the sync separator must have negative-going sync, which can be
obtained from synchronous demodulators such as TDA2540, TDA2541 and TDA2670.
The slicing level of the sync separator is determined by the value of the resistor between pins 3 and 4.
A 5,6 kfl resistor provides a slicin
g level midway between the top sync level and the blanking level.Thus the slicing level is independent of the amplitude of the sync pulse input at pin 2.
The nominal top sync level at pin 2 is 1,5 V, and the amplitude selective noise inverter is activated at
0,7 V. The horizontal phase detector has a steepness of 1,2 V/its and together with the 1800 Hz/V of
the horizontal oscillator provides a total control steepness of 2000 Hz/us.
A second horizontal phase detector provides a 5,5 its pulse which ensures symmetrical gating of the
horizontal synchronization. During catching the gating is automatically switched off. At the same time
the flywheel filter is switched to a short time constant. The value of this time constant can be deter~
mined externally via pin 11.
When the indirect vertical sync output is generated by the 625 divider system an anti-top flutter pulse
switches off the equalizing and vertical sync pulse operation of the phase detector. Thus top flutter
distortion of the control voltage due to vertical pulses can be anticipated. When the 625 divider system
is in the direct mode the anti~top flutter pulse is inhibited.
The free running output frequency of the horizontal oscillator is 31,25 kl-lz. The vertical frequency
output is obtained by dividing this double horizontal frequency by 625. The double horizontal
frequency is fed via a binary divider to provide the normal 15,625 kHz horizontal output at pin 8. The
trailing edge of this pulse is positioned 0,9 us after the end of the video sync pulse input at pin 2
(see Fig. 2).
The automatic vertical sync block contains the following:
0 625 divider
0 In/out-sync detector
I Direct/indirect sync switch
O Identification circuit
It is fed by a signal obtained by integration of the composite sync signal and an internally generated,
clipped video signal. The vertical sync pulse is sliced out of this integrated signal by an automatically
biased clipper. The videopart of the signal helps to build up a vertical sync pulse when heavy negative-
going reflections (mountains) distort the video signal. The in/out sync-detector considers a signal
out~of-sync when fifteen or more successive incoming vertical sync pulses are not in phase with a
reference signal from the 625 divider. Therefore a distorted vertical sync signal needs only one
out-of-fifteen pulses to be in phase to keep the system in sync. When the sixteenth successive out-of-
sync pulse is detected, the direct/indirect sync switch is activated to feed the vertical sync signal
directly out of the block at pin 2 (direct sync vertical output).
At the same time the 625 divider is reset by one of the sync pulses. After the reset pulse, if the 7th
sliced vertical sync pulse coincides with a 625 divider window, the sync output pulse is presented
again by the divider system and switch-over to indirect mode occurs.
In the direct mode, every 7th non-coinciding sliced vertical sync pulse will reset the counter. Thus a
non-standard video signal will result in continuous reset pulses and the direct/indirect switch will
remain in the direct position.
To avoid delay in vertical synchronization, caused by waiting time of the divider circuit after channel
change or an unsynchronized camera change in the studio, information is fed from the horizontal coin-
cidence detector to the automatic switch for the vertical sync pulse. The loss of horizontal synchroni-
zation sets the automatic switch to direct vertical sync. When horizontal coincidence is detected again
the setting of the automatic switch depends on whether a standard video signal is received or not. When
an external voltage between 2,5 V and 7,25 V is applied via pin 12 to the coincidence detector, the hor-
izontal phase detector is swsync. A voltage level on pin 12 > 8,25 V switches the horizontal phase detector to a short time constant,
without affecting the indirect/direct vertical sync system which remains operational.
The video transmitter identification circuit detects when a sync pulse occurs during the internal gating
pulse. This indicates the presence of a video transmitter and results in the capacitor connected to pin
10 being charged to 8 V. When no sync pulse is present the capacitor discharges to < 1 V. The voltage
at pin 10 is compared with an internal d.c. voltage. The identification output at pin 9 is active when
pin 10 is < 1,6 V (no video transmitter) and inactive (high impedance) when pin 10 is > 3,5 V.
The vertical sync output pulse at pin 1 is inhibited when no video transmitter is identified, which
prevents interference or noise affecting the frequency of the vertical output stage. This results in a vertical stable picture, plus vertical stable position information of tuning systems.
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