In this era MIVAR had developed small chassis, so called essential, which have all functions put toghether in 3 main boards.
The tellye has a frequency synthesized tuning system with direct selection of 99 Channels and
manual search functions.
And it started using the TDA3562A instead of the TDA3560
Left: Signal processing or small signal panel
Centre: Synchronization + Frame deflection output
Right: Power supply and line output + EHT.
On the bottom of the plastic cabinet there is the ST-BY supply unit.
- Video chrominance and Luminance with TDA3562A
.LUMINANCE SIGNAL PROCESSING WITH
.HORIZONTAL AND VERTICAL BLANKING
.LINEAR TRANSMISSION OF INSERTED
.LINEAR CONTRAST AND BRIGHTNESS
CONTROL ACTING ON INSERTED AND MATRIXED
.AUTOMATIC CUT-OFF CONTROL
.NTSC HUE CONTROL
The TDA3562A is a monolithic IC designed as
decode PAL and/or NTSC colour television standards
and it combines all functions required for the
identification and demodulation of PAL and NTSC
TDA1180P TV HORIZONTAL PROCESSOR
The TDA1180P is a horizontal processor circuit for
b.w. and colour monitors. It is a monolithic integrated
circuit encapsulated in 16-lead dual in-line
Pin 1 - Positive supply
The operating supply voltage of the device ranges
from 10V to 13.2V
Pin 2 and 3 - Output
The outputs of TDA1180P are suitable for driving
transistor output stages, they deliver positive pulse
at Pin 3 and negative pulse at Pin 2.
The negative pulse is used for direct driving of the
output stage, while positive pulse is useful when a
driver stage is required.
The rise and fall times of the output pulses are
about 150 ns so that interference due to radiation
Furthermore the output stages are internally protected
against short circuit.
Pin 4 - Protection circuit input
By connecting Pin 4 of the IC to earth the output
pulses at Pin 2 and 3 are shut off ; this function has
been introduced to produced to protect the final
stages from overloads.
The same pulses are also shut off when the supply
voltage falls below 4V.
Pin 5 - Phase shifter filter
To compensate for the delay introduced by the line
final stages, the flyback pulses to Pin 6 and the
oscillator waveform are compared in the oscillatorflyback
pulse phase comparator.
The result of the comparison is a control current
which, after it has been filtered by the external
capacitor connected to Pin 5, is sent to a phase
shifter which adequately regulates the phase of the
The maximum phase shift allowed is: td = tp - tf
where tf is the flyback pulse duration.
Pin 5 has high input and output resistance (current
Pin 6 - Flyback input
The flyback pulse drives the high impedance input
through a resistor in order to limit the input current
to suitable maximum values.
The flyback input pulses are processed by a double
threshold circuit; this generates the blanking pulses
by sensing low level flyback voltage and the pulses
to drive the phase comparator by sensing high level
flyback voltage, therefore phase jitter caused by
ringing normally associated with the flyback pulse,
Pin 7 - Key and blanking pulse output
The key pulse for taking out the burst from the
chrominance signal is generated from the oscillator
ramp and has therefore a fixed phase position with
respect to the sync.
The key pulse is then added internally to the blanking
pulse obtained by correctly forming the flyback
pulse present at Pin 6.
The sum of the two signals (sandcastle pulse) is
available on low impedance at output Pin 7.
Pin 8 and 9 - Sync separators inputs
The video signal is applied by means of two distinct
biasing networks to pins 8 and 9 of the IC and
therefore to the respective vertical and horizontal
The latter take the sync pulses out of the video
signal and make them available to the rest of the
circuit for further processing.
Pin 10 - Vertical sync output
The vertical sync pulse, obtained by internal integration
of the synchronizing signal, is available at
The output impedance is typically 10kW and the
lowest amplitude without load is 11V.
Pin 11 - Coincidence detector
From the oscillator waveform a gate pulse 7 ms
wide is taken whose phase position is centered on
the horizontal synchronism.
The gate pulse not only controls a logic block which
permits the sync to reach the oscillator-sync phase
comparator only for as long as its duration, but also
allows the latching and de-latching conditions of
the oscillator to be established.This function is
obtained by a coincidence detector which compares
the phase of the gate pulses with that of the
When the two signals are not accurately aligned in
time it means that the oscillator is not synchronized.
In this case the detector acts on the logic block to
eliminate its filtering effect and on the time constant
switching block to establish a high impedance on
Pin 12 (small time constant of low-pass filter).
This latter block also acts on the oscillator-sync
phase detector to increase its sensitivity and with it
the loop gain of the synchronizing system.
In this conditions the phase lock has low noise
immunity (wide equivalent noise bandwidth) and
rapid pull-in time which allows fairly short synchronization
Once locking has taken place the coincidence detector
enables the logic block, causes a low impedance
on Pin 12 and reduces the sensitivity of the
In these conditions the phase lock has high noise
immunity ( narrow equivalent noise bandwidth) due
to the complete elimination of interference which
occurs during the scanning period and the greater
inertia with which the oscillator can change its
To optimize the behaviour of the IC if a video
recorder is used, the state of the detector can be
forced by connecting Pin 11 to earth or to + VS. The
characteristics of the phase lock thus correspond
to the lack of synchronization.
Pin 12 - Time constant switch, (see Pin 11)
Pin 13 - Control current output
The oscillator is synchronized by comparing the
phase of its waveform with that of the sync pulses
in the oscillator-sync phase comparator and sending
its output current I13 (proportional to the phase
difference between the two signals) to Pin 15 of the
oscillator after it has been filtered properly with an
external low-pass circuit.
The time constant of the filter can be switched
between two values according to the impedance
presented by Pin 12.
The voltage limiter at the output of the phase
comparator limits the voltage excursion on Pin 13
and therefore the frequency range in which the
oscillator remains held-in.
The output resistance of Pin 13 is:
l low when V13 > 4.3 or V13 < 1.6V
l high when 1.6V < V13 < 4.3V
To prevent the vertical sync from reaching the
oscillator-sync phase comparator along with the
horizontal sync,a signal which inhibits the phase
detector during the vertical interval is taken from
the vertical output stage; inhibition remain even if
the video signal is not present.
The free running frequenc of the oscillator is determined
by the values of the capacitor and of the
resistor connected to Pins 14 and 15 respectively.
To generate the line frequency output pulses, two
theresholds are fixed along the fall ramp of the
triangular waveform of the oscillator.
Pin14 - Oscillator (see Pin 13)
Pin 15 - Oscillator control current input (see
Pin 16 - Ground
TDA2541 IF AMPLIFIER WITH DEMODULATOR AND AFC
.SUPPLYVOLTAGE : 12V TYP .SUPPLYCURRENT : 50mATYP .I.F. INPUT VOLTAGE SENSITIVITY AT
F = 38.9MHz : 85mVRMS TYP .VIDEO OUTPUT VOLTAGE (white at 10% of
top synchro) : 2.7VPP TYP .I.F. VOLTAGE GAIN CONTROL RANGE :
64dB TYP .SIGNAL TO NOISE RATIO AT VI = 10mV :
58dB TYP .A.F.C. OUTPUT VOLTAGE SWING FOR
Df = 100kHz : 10V TYP
The TDA2540 and 2541 are IF amplifier and A.M.
demodulator circuits for colour and black and white
television receivers using PNP or NPN tuners. 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
TDA1170 vertical deflection FRAME DEFLECTION INTEGRATED CIRCUIT
GENERAL DESCRIPTION f The TDA1170 and TDA1270 are monolithic integrated
circuits designed for use in TV vertical deflection systems. They are manufactured using
the Fairchild Planar* process.
Both devices are supplied in the 12-pin plastic power package with the heat sink fins bent
for insertion into the printed circuit board.
The TDA1170 is designed primarily for large and small screen black and white TV
receivers and industrial TV monitors. The TDA1270 is designed primarily for driving
complementary vertical deflection output stages in color TV receivers and industrial
APPLICATION INFORMATION (TDA1170)
The vertical oscillator is directly synchronized by the sync pulses (positive or negative); therefore its free
running frequency must be lower than the sync frequency. The use of current feedback causes the yoke
current to be independent of yoke resistance variations due to thermal effects, Therefore no thermistor is
required in series with the yoke. The flyback generator applies a voltage, about twice the supply voltage, to
the yoke. This produces a short flyback time together with a high useful power to dissipated power
MIVAR 16C1V CHASSIS 2568 + 2247 + 2260 MIVAR POWER SUPPLY COMBINED WITH BU208A TRANSISTOR HORIZONTAL DEFLECTION CIRCUIT, EXPLANATION AND CONCEPT VIEW.
Circuit arrangement for generating a sawtooth deflection current through a line deflection coil:
1. Circuit arrangement for generating a sawtooth deflection current flowing through a line deflection coil in an image display apparatus, which circuit arrangement comprises a deflection network including trace and retrace capacitor means coupling to said coil, and a first diode coupled to said retrace capacitor through which the deflection current flows during part of the trace interval, means for conveying the deflection current during the remainder of the trace interval including a second diode and a controllable switch coupled to said diode, said switch and second diode together being coupled in parallel with the first diode, the circuit arrangement further comprising an inductive element coupled to the switch, a third diode coupled to the deflection network and to said inductive element, a transformer having a core of a magnetic material and a winding, and a capacitor coupled to said winding and to the deflection network, characterized in that the inductive element is coupled via the third diode to the series combination of the above-mentioned series capacitor and part of the transformer winding less than all of said winding.
2. Circuit arrangement as claimed in claim 1, in which the inductive element comprises a winding, characterized in that the winding of the inductive element is wound on the transformer core.
3. Circuit arrangement as claimed in claim 1, characterized in that a first capacitor is coupled in parallel with the said part of the transformer winding and a second capacitor is coupled in parallel with the remainder of the winding, the ratio between the reactances of the said capacitors being equal to the ratio between the number of turns of the said parts of the winding.
4. Circuit arrangement as claimed in claim 1 in which the inductive element has a primary winding and a secondary winding which are coupled with one another, characterized in that the ratio of the number of turns of the secondary winding to that of the primary winding is substantially equal to ##EQU19## where m is the ratio of the turns number of the part of the transformer winding between the connection to the third diode and the series capacitor to the turns number of the entire winding, α is the ratio of the amplitude of the retrace voltage to the trace voltage, and δmax is the value of that ratio of the conduction time of the switch to the line period which is associated with the maximum value of a voltage supply source which supplies energy to the circuit arrangement.
5. A circuit arrangement as claimed in claim 1 wherein said core has two limbs, a tapped transformer winding and at least one high-voltage winding wound on one limb, a primary winding and a secondary winding wound on the other limb, the ratio of the number of turns of the secondary winding to that of the primary winding being greater than the ratio of the number of turns of the part of the transformer winding between the tapping and an end adapted to be connected to a series capacitor to the number of turns of the entire winding and being less than 1.
Such a circuit arrangement is described in "IEEE Transactions on Broadcast and Television Receivers," August 1972, volume BTR-18, Nr. 3, pages 177 to 182, and is a combination of a line deflection circuit and a switched-mode supply voltage stabilizing circuit, the controllable switch being used to perform both the said functions. This known circuit arrangement has the advantage that it can be fed with an unstabilised supply voltage and is capable of supplying a satisfactorily stabilized deflection current, a stabilized high voltage and, if desired, auxiliary voltages, the stabilization being obtained by control of the conduction time of the swtich.
When such a circuit arrangement is to be designed, amongst other problems the three following ones arise. Firstly care must be taken to ensure that the maximum voltage set up across the switch (a transistor) during the retrace interval does not exceed the permissible limit value for this element. Secondly the variation of the conduction time of the transistor must be capable of accommodating the supply voltage variations to be expected. Thirdly the (stabilized) trace capacitor voltage applied to the deflection coil during the trace interval must be selectable at will, for with a given deflection coil this voltage determines the intensity of the deflection current produced.
The said problems are not independent of one another. If, for example, the trace voltage is low, the maximum collector voltage of the transistor also is low; it may be further reduced by making the conduction time of the transistor as short as possible. It will therefore be clear that several degrees of freedom are required. One degree of freedom is available to a certain extent, namely the transformation ratio between two windings of the inductive element, one winding being connected between a terminal of the supply voltage source and the junction point of the collector and the second diode, whilst the other winding, which is coupled to the first one, is connected to the third diode, for the choice of the said ratio enables a freer choice of the trace voltage. However, the two other problems, specifically that of maximum collector voltage, are not solved thereby.
It is an object of the present invention to provide a circuit arrangement having one more degree of freedom, permitting the maximum permissible collector voltage to be freely determined, and for this purpose the circuit arrangement according to the invention is characterized in that the inductive element is connected via the third diode to the series combination of the abovementioned series capacitor and part of the transformer winding.
The introduction of a new parameter not only enables the maximum collector voltage to be reduced without the trace voltage being affected but also proves to enable a larger range of supply voltage variations to be accommodated. Hence, the step according to the invention permits of designing a circuit arrangement in which conflicting requirements can simultaneously be satisfied.
In a possible embodiment in which the inductive element has a winding the circuit arrangement is characterized in that the winding of the inductive element is wound on the transformer core.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which
FIG. 1 is a circuit diagram showing schematically the basic elements of an embodiment of the circuit arrangement according to the invention,
FIG. 2 shows waveforms of voltages produced in said embodiment,
FIGS. 3a and 3b show graphs which may be used in the selection of the parameters, and
FIG. 4 is a circuit diagram of a modified part of the circuit arrangement of FIG. 1.
The circuit arrangement shown in FIG. 1 includes a driver stage Dr to which signals from a line oscillator, not shown, are applied and which delivers switching pulses to the base of a switching transistor Tr. One end of a primary winding L 1 of a transformer T 1 is connected to the collector of the transistor Tr, which is of the n-p-n type, the other end of the winding L 1 being connected to the positive terminal of a direct-voltage source B to the negative terminal of which the emitter of the transistor Tr is connected. This negative terminal may be connected to the earth of the circuit arrangement.
A trace capacitor C t is connected in series with a line deflection coil L y of the image display apparatus, not shown further, of which the circuit arrangement of FIG. 1 forms part, the resulting series combination being shunted by a diode D 1 having the conductive direction shown and by a retrace capacitor C r . The capacitor C r may alternatively be connected in parallel with the coil L y . The said four elements represent the schematic circuit diagram including the basic elements of the deflection section only. This section may, for example, in known manner be provided with one or more transformers for mutual coupling of the elements, with devices for centering and linearity correction and the like.
A secondary winding L 2 of the transformer T 1 is connected to the anode of a diode D 3 , and the anode of a diode D 2 is connected to the junction point A of the elements D 1 , C r and L y . The cathode of the diode D 2 is connected to the collector of the transistor T r whilst the cathode of the diode D 3 is connected to a tapping Q on a winding L 3 of a transformer T 2 . One end of the winding L 3 is connected to the point A, the other end being connected to earth via a capacitor C 1 . The core of the transformer T 2 carries further windings across which voltages are produced which serve as supply voltages for other components of the image display apparatus. FIG. 1 shows one of said windings, the windings L 4 , which by means of a rectifier D 4 produces a positive direct voltage across a smoothing capacitance C 2 . One of said windings, for example the winding L 4 , is the high voltage winding, so that the voltage set up across the capacitor C 2 is the high voltage for the final accelerating anode of the display tube (not shown). The free ends of the windings L 2 and L 4 are connected to earth, and the winding senses of the windings shown are indicated in the Figure by polarity dots.
The operation of the circuit arrangement is similar to that described in the abovementioned paper and may be summarized as follows. During a first part of the line trace interval the diode D 1 is conducting. The voltage across the capacitor C t is applied to the deflection coil L y through which a sawtooth deflection current i y flows. At a given instant the transistor TR becomes conducting. When in about the middle of the trace interval the current i y reverses direction the diode D 1 is cut off, so that the current i y then flows through the diode D 2 and the transistor Tr. At the end of the trace interval the transistor Tr is cut off. As a result an oscillation, the retrace pulse, is produced across the capacitor C r whilst the energy derived from the source B and stored in the winding L 1 causes a current to flow through the diode D 3 . When the voltage across the capacitor C r has become zero again, the diode D 1 becomes conducting: this is the beginning of a new trace interval. The diode D 3 remains conducting until the transistor Tr is rendered conducting, the energy stored in the winding L 2 being transferred to the winding L 1 . Stabilisation is provided, for example, by feeding back the voltage across the capacitor C t to the driver circuit Dr, in which a comparison stage and a modulator ensure that the conduction time of the transistor Tr is varied so that the said voltage and hence the amplitude of the deflection current remain constant. Compared with the known case in which the cathode of the diode D 3 is connected to the point A instead of to the tapping Q operation is different, the difference being as follows. In the known case the current passed by the diode D 3 flows to earth via the diode D 1 during the first part of the trace interval. In the arrangement shown in FIG. 1, during this same part energy is stored in the series combination L 3 , C 1 . The voltage v A across the capacitor C r , the voltage v c at the collector of the transistor T r and the voltage v 1 across the winding L 1 are plotted against time in FIGS. 2 a, 2b and 2c respectively. The symbol T indicates the line period, τ 1 indicates the retrace interval, τ 2 that part of the period T in which the transistor Tr is non-conducting, and τ 3 = δ T indicates the part of the period T in which this transistor is conducting. The number δ is the ratio between the time τ 3 and the period T.
The voltage v A consists of the retrace pulse of amplitude V during the time τ 1 and is zero during the time τ 2 . At the instant at which the transistor Tr is rendered conducting, i.e. the instant of transition t 1 between τ 2 and τ 3 , the voltage v C becomes substantially zero. Thus the volage V B of the source B is set up across the winding L 1 .
In the circuit arrangement of FIG. 1 two ratios are significant, namely the transformation ratio between the windings L 1 and L 2 , i.e. the ratio between the number of turns of the winding L 1 and that of the winding L 2 , which is equal to 1 : p, and the ratio of the turns number of the entire winding L 3 and that of the part of this winding between the tapping Q and the end connected to the capacitor C 1 , which ratio is 1 : m. First it will be assumed that the points Q and A coincide (m = 1).
During the time τ 3 the voltage cross the winding L 2 is equal to -pV B . During the time τ 1 the voltage v c is equal to V/p + V B . Let V o be the direct voltage across the capacitor C t , if the capacitance of this capacitor is large enough, or the direct voltage component of the voltage across this capacitor, if it has a comparatively small capacitance for the purpose of the S correction; in either case it is equal to the mean value of the voltage v A , for no direct-voltage component can be set up across the coil L y . The capacitor C 1 has a large capacitance, so that a direct voltage equal to V o is set up across it. The following equation applies: ##EQU1##
The mean value of the voltage across the winding L 3 also is zero, so that the equation applies: ##EQU2## In this formula the integral can be substituted, Yielding V o T = pV B . τ 3 , that is; V o = pδ. V B (1)
At given values of the ratios δ and p the diode D 2 will conduct during the time τ 1 . Because during this time the diode D 3 is conducting, the windings L 1 and L 2 will be short-circuited by the diodes D 2 and D 3 , causing the retrace pulse across the capacitor C r to be clipped and the deflection current to be distorted. U.S. Pat. Application No. 443,863 filed Feb. 19, 1974 describes steps for avoiding such an effect, for example by including in series with the diode D 2 a transistor which is cut off during the time τ 1 . A capacitor C 3 is connected between the ends of the windings L 1 and L 2 or between tappings thereon for the purpose of preventing the occurrence of parasitic oscillations which may be produced by the leakage inductance between the said windings in a manner such that no line-frequency voltage is set up across the capacitor C 3 . FIG. 1 shows the case where p <1.
The maximum value of the collector voltage v c of the transistor is equal to ##EQU3## where α is the ratio V/V o which depends upon the retrace ratio Z = τ1/T. The maximum value of V c is obtained when V B has its maximum value V B max, for which δ has the value δ min , for from the relationship (1) it follows that δ and V B are inversely proportional to one another because the voltage V o is maintained constant.
The voltage V o can be chosen by choosing the ratio p, so that the deflection current y is determined for a given deflection coil L y . However, from the above it follows that the maximum value of the voltage V c , which is highly critical for the transistor, is not controllable. Moreover, the relationship (1) can be written:
V o = p δ min . V B max = p δ max . V B min, where V B min is the minimum value of V B for which δ = δ max , and from which follows: ##EQU4## The ratio δ min has its minimum value δ 1 if the instant t 1 coincides with the middle of the trace interval, and δ max has its maximum value δ 2 if the instant t 1 coincides with the beginning t o of the trace interval. Hence the above ratio cannot exceed 2, so that the arrangement cannot accommodate larger variations of the voltage V B .
According to the invention the points A and Q do not coincide. The voltage across the winding L 3 is equal to v A - V o so that the voltage v Q in the point Q is equal to v Q = V o + m(v A - V o ) = mv A + (1 - m) V o . With the aid of the waveform of the voltage v A of FIG. 2a the waveform of the voltage v 1 across the winding L 1 between the positive terminal of the source B and the collector of the transistor Tr can be plotted (FIG. 2c), allowing for the fact that the diode D 3 is conducting during the times τ 1 and τ 2 .
Thus we have: ##EQU5## during time τ 3 : v 1 = - V B . Writing the condition for the mean value of the voltage v 1 being zero after some calculations yields. ##EQU6## The maximum value of the collector voltage v c is ##EQU7## from which follows: ##EQU8## after substitution of the formula (2). It can be shown that this function steadily decreases with decrease of the ratio m. It is plotted in FIG. 3a for z = 0.2, from which follows α ≉ π/2z ≉ 7,8, and with δ min = δ 1 = 1/2 (1 - z) = 0.4. The Figure shows that by making m less than 1 a reduction of the maximum collector voltage is obtained and that this result is independent of the ratio p.
From the formula (2) the following relationship can be derived: ##EQU9## ##EQU10## This function also is independent of the ratio p and it increases as m decreases. It is plotted in FIG. 3b for δ min = δ 1 = 0.4 and δ max = δ 2 = 0.8 (Z = 0.2), so that the entire δ range is used, whilst the Figure shows that a larger range of supply voltage variations can be accommodated, for when m is less than 1 the ratio V B max /V B min exceeds 2.
Similarly to the preceding case, the voltage V o can be determined by the choice of the ratio p. If the means described in the abovementioned U.S. Pat. Application No. 443,863 are to be dispensed with, it is found that an upper limit can be set to p. The diode D 2 will just be conducting during the time δ 1 if the lowest value of the voltage V c which is found in practice, that is ##EQU11## is equal to the voltage V. In the above expression, according to the formula (2), ##EQU12## from which we can derive: ##EQU13##
The above will be explained by means of two numerical examples. If the voltage V B can vary between 230 volts and 345 volts (with a mains voltage of 220 volts) V B max /V B min is less than 2, so this does not provide difficulty. If the transistor Tr is not capable of withstanding a voltage exceeding 1200 volts, it will be seen from FIG. 3a that m = 0.64. From the formula (2) it follows that ##EQU14## with δ min = δ 1 and ##EQU15## so that δ max = 0.56 < δ 2 . The formula (5) yields: ##EQU16## so that V o = 0.87 times 161 = 140 volts.
If now the voltage V B can vary between 115 volts and 345 volts (the mains voltage is 110 volts or 220 volts), then V B max /V B min = 3. FIG. 3b shows that m = 0.38, for which FIG. 3a yields V c max = 2.9 times 345 = 1000 volts. Formula (2) yields: ##EQU17## whilst ##EQU18## so that V o = 0.54 times 183 volts = 99 volts. Because m cannot be increased, a higher V o if desired requires p to exceed 0.54, and hence the step according to the abovementiond Patent Application must be used.
Similarly to what is the case in U.S. Pat. Application No. 473,771, filed June 1, 1973, the cores of the transformers T 1 and T 2 of FIG. 1 may be one and the same core, that is to say the windings L 1 , L 2 and the winding L 3 may be coupled to one another in spite of the fact that voltages of different waveforms are set up across the said windings. This is possible because the said voltage waveforms are not affected by the coupling, since the voltages V o and V B are "hard," that is to say they are externally impressed, and hence are not affected by the coupling. The currents flowing through the windings, however, are affected. In the lastmentioned Patent Application it is shown that the operation of the circuit arrangement is not adversely affected thereby, but on the contrary important advantages are obtained. It should be mentioned that instead of the tapping Q an additional winding may be wound on the same core as the winding L 3 , which additional winding has a smaller number of turns than the winding L 3 and is included between the cathode of the diode D 3 and the junction point of L 3 and the capacitor C 1 .
Formula (5) shows that the ratio m should not be excessively small, because in this case the ratio p also is small, with the result that large currents flow on the secondary side of the transformer T 1 . In addition, large currents then will flow through the leakage inductance of the said transformer, which gives rise to ringing at the instant t 1 . Furthermore difficulties will arise in designing the abovementioned embodiment using a single transformer. If for these reasons the formula (5) is not complied with, that is to say if p is made greater than the preferred value p max , the steps according to the abovementioned U.S. Pat. Application No. 443,863 have to be employed. This requires an additional transistor, which is expensive, or an additional diode, which does not prevent the production of a high V c max, whilst it was the very purpose of using a low m to obtain a low V c max.
In practice there is a leakage inductance between the two parts of the winding L 3 . In FIG. 4, which shows only part of the circuit arrangement, this leakage inductance is shown as an inductance L 5 between the point Q and an imaginary tapping Q' on the winding L 3 . The inductance L 5 prevents abrupt current transistions which in conjunction with the stray capacitances may give rise to ringing. This can be avoided by connecting a capacitor C 4 between points A and Q and a capacitor C 5 between the point Q and the junction point of the winding L 3 and the capacitor C 1 . If the ratio between the reactances of C 4 and C 5 is equal to that between the numbers of turns of the upper and lower parts of the winding L 3 , no alternating voltage is set up across the inductance L 5 so that no ringing can occur. The parallel connection of the capacitor C r and of the network C 4 , C 5 together with the inductive components of the circuit arrangement results in a resonant frequency the period of which is about equal to twice the time τ 1 .
Hereinbefore it has been assumed that the capacitance of the capacitor C 1 is sufficiently large to enable the voltage across it to be regarded as constant (= V o ). It should be mentioned that this is necessary only if one or more of the auxiliary voltages produced by means of windings of the transformer T 2 are obtained by means of trace rectification.
A combination deflection circuit and switching mode power supply uses only a single switching element. Across certain diodes in this circuit is a stable voltage. A capacitor and a transformer primary are series coupled to each other and together parallel coupled across at least one of the diodes. A rectifier is coupled to the transformer secondary to provide power to other portions of a television set.
1. A line deflection circuit for generating from a direct voltage source a sawtooth current flowing through a deflection coil, said circuit comprising a parallel resonant circuit comprising said coil, a trace capacitor coupled to said coil, and a retrace capacitor coupled to said coil; a first diode coupled to said retrace capacitor, the deflection current flowing during a first part of the trace period through said first diode and during a second part of the trace period through a controllable switch, energy being applied from said direct voltage source during the trace period to a first winding arranged between said direct voltage source and the switch, and being applied through a second diode conducting during the retrace period from a second winding to the parallel resonant circuit which is connected to the switch through a third diode conducting during the second part of the trace period, at least one of the second and third diodes being shunted by the series arrangement of a capacitor and a primary winding of a current supply transformer, and means for rectifying coupled to said transformer for the direct current supply to other stages of the device. 2. A circuit as claimed in claim 1 wherein said switch comprises a transistor. 3. A circuit for generating from a direct voltage source a sawtooth current having trace and retrace periods through a deflection coil, said circuit comprising a trace capacitor, means for coupling said trace capacitor to said coil, a retrace capacitor coupled to said trace capacitor, diode coupled to said retrace capacitor, a first diode means coupled to said retrace capacitor for conveying said current during a first part of said trace period, a first winding having a first end means for coupling to said source and a second end, a controllable switch means coupled to said second end for conveying said current during a second part of said trace period, a second winding, a second diode means coupled between said first diode and said second winding for conducting during said retrace period, a third diode means coupled between said first diode and said switch for conducting during said second part of said trace period, and means for supplying direct current power comprising a transformer having primary and secondary windings, a capacitor series coupled to said primary, said primary and capacitor being parallel coupled to at least one of said second and third diodes, and a rectifier coupled to said secondary. 4. A circuit as claimed in claim 3 wherein said switch comprises a transistor.
Such a circuit arrangement is known from "IEEE Transaction on Broadcast and Television Receivers", August 1972, vol. BTR-18, No. 3, pages 177 to 182. The known circuit arrangement is the combination of a transistorized line deflection stage for a television receiver and a stabilised switch mode power supply, whereby one single switching element, the above mentioned transistor is both the switching transistor and the line deflection transistor.
An object of the invention was to further develop this circuit arrangement. It was found that an alternating voltage is present at the above mentioned second and third diode, which voltage is stabilized. The object according to the invention was to utilize this available and unilaterally stabilized rectangular voltage in a particularly advantageous manner.
This object is solved in that in a line deflection circuit of the kind described in the preamble the second and/or third diode is shunted by the series arrangement of a capacitor and a primary winding of a current supply transformer serving via rectifying for the direct current supply to other stages of the device.
An embodiment of the invention is shown in the drawings and will be further described hereinafter.
FIG. 1 shows the circuit improved according to this invention.
FIG. 2 shows different voltage variations as a function of time.
For the description of FIG. 1 the description of the Figures of the previously cited known circuit may be essentially used as a reference. A transformer is denoted by T1, a primary winding is L1; it is connected through a coupling capacitor CK to a secondary winding L2. A direct voltage source is UB. Furthermore a winding L3 is provided on the transformer secondary side which may serve for the high voltage generation UH through the diode Db.
The switching transistor is TR; rectangular pulses with the line frequency and originating from a driver stage (not represented) are applied to this transistor. The entire circuit arrangement thus serves for generating a sawtooth current flowing through a deflection coil L. The deflection coil L is part of a parallel resonant circuit consisting of a retrace capacitor C2, the deflection coil L itself and a trace capacitor C3.
In the operative condition a first diode D2 which is parallel connected to the said resonant circuit conducts during a first part of the trace period and conveys the negative part of the deflection current I 2 during the period from t1 to t3 (compare FIG. 2d). During this period the switching transistor TR is separated from the deflection circuit consisting of D2, L, C2, C3 by a third diode Dd biassed in the blocking direction.
At the instant t2 which is adjustable via the width of the rectangular pulses (compare FIG. 2f) at the base of TR, TR is rendered conducting. As a result a current can flow through L1 and TR which stores until the switch-off instant t4 the energy required for operating the circuit in L1. This energy is applied to the deflection circuit at the initiation of the retrace period t4 so as to compensate for losses. This energy storage is ended at the instant t1 of the new period.
Meanwhile the zero crossing of the deflection current occurs at instant t3. D2 is blocked. Due to the polarity change of the current I L the third diode Dd becomes conducting and the deflection current may be taken over by the switching transistor TR. This current is superimposed uninterfered on the part of the collector current originating from the power supply function of TR.
Thus the deflection function of the circuit in addition to the power supply function is ensured. This function may be influenced by shifting the instant t2. The limits of the control range are at t1 and t3. By comparison, for example, of the voltage UA over the diode D2 in the retrace period with a reference voltage a control magnitude for t2 can be derived. A stabilisation of the deflection in case of mains voltage and beam current fluctuations is then possible.
It is often essential to provide further stages in the television display apparatus with a stabilized voltage. Conventionally such supply voltages are obtained by trace rectification on an auxiliary winding of the line transformer. In this circuit this simple possibility is not given due to the connection with the power supply function. As can be seen in FIG. 2a the secondary voltage US consists of a rectangular voltage on which the flyback pulse of the deflection circuit is superimposed. When the trace part of US is rectified no stabilized direct voltage can be obtained due to the duty cycle variations caused by the control since the value of the voltage US between the instants t 2 and t 4 depends on that of the voltage UB.
A flyback rectification is feasible in this case. However, due to the small conduction angle an inadmissibly high internal resistance of the obtained supply voltage is to be taken into account.
According to the invention a rectangular voltage present alternatively across the diodes D1 and D2, respectively is used. These voltages do not contain a flyback pulse FIG. 2c shows the voltage variation UN on the secondary side L5 of a transformer T2 introduced for potential separation. A primary winding L 4 thereof is arranged in series with a capacitor C 4 and this series arrangement shunts the diode D1. The capacitor C 4 prevents a dc short circuit of the diode D1 by the winding L 4 and has a capacitance which is large enough for preventing an influence upon the variation of UN. The voltage across the capacitor C 4 is thus equal to the dc-component of the voltage across the capacitor C 3 , which component is stabilised since the voltage UA is. The voltage across the winding L 4 is equal to the difference between that across the diode D1 and that across the capacitor C 4 , the first mentioned voltage being equal to U A -U S . The voltage UN across the winding LS, which winding has the indicated winding sense, has the variation shown in FIg. 2c and between the instants t o and t 2 it is equal to the stabilised dc-component of the voltage present across the capacitor C 3 . The voltage UN is rectified with the aid of a diode DN and smoothed with the aid of a capacitor CN. The rectified voltage UL is applied to the parts of the apparatus using a low voltage which in this case are represented by a load resistor RL.
DN must have such a polarity that it conveys current during the time t o -t 2 . Then the rectified voltage is stabilised to the same extent as the deflection voltage. The conduction angle is large so that the internal impedance of the voltage source is low. The primary side L4 of the transformer T2 is connected to D1 as is shown in FIG. 1. D1 and DN are then conducting simultaneously so that the internal resistance of UN is further reduced. In the same manner the series arrangement of L4 and C4 in parallel with Dd is alternatively possible.
The transformer T2 may be formed with a relatively small core due to the high operating frequency. On account of the switching properties (Dd and D1 alternately conducting) the rectangular voltage cannot become larger than the direct voltage on CK (corresponds to the voltage UB). Overvoltages as a result of for example picture tube flash-overs are thus prevented.