The THOMSON CHASSIS ICC5 Is a highly engineered chassis (see pictures).
It was introducing high integration of advanced and high precision functions.
It's introducing all digital control of all circuits, from tuning to video matrix and audio.
It was fitted in a very high number of models with screen formats varying from 20 to 32 Inches.
It has known a high rate of improvements and add ons fetures and further functions.
The version here in collection is the second version marketed in 1986 when the ICC5 was developed (5110) which eliminates the reset ic but keeping the basic design here shown.
It has a layout design which is very complex due to high engineering on signal path toghether with integration needings.
Functionally they run very well and stable but it was showing the highest rate of failures caused by dry joint evn almost immediately when new !! !!
To run these in reliable way you have to basically rework all the PCB Joint !!
THE SET HERE SHOWN WAS NEVER SERVICED WHICH IS QUITE RARE FOR A THOMSON ICC5 CHASSIS.
Quality of components it's very high, all parts here pictured are original from 1986.
Picture produced by this chassis is excellent and this is expecially coming from the accurate and high performed video signal processing.
THOMSON TF5551 PG5 THOMSQUARE (ICC5) CHASSIS ICC5 (5116) COLOR TV SCANNING AND POWER SUPPLY PROCESSOR TEA2029C
The TEA2029C is a complete (horizontal and vertical)
deflection processor with secondary to primary
SMPS control for color TV sets.
DEFLECTION .CERAMIC 500kHz RESONATOR FREQUENCY
REFERENCE .NO LINE AND FRAME OSCILLATOR ADJUSTMENT
.DUAL PLL FOR LINE DEFLECTION .HIGH PERFORMANCE SYNCHRONIZATION .SUPER SANDCASTLE OUTPUT .VIDEO IDENTIFICATION CIRCUIT .AUTOMATIC 50/60Hz STANDARD IDENTIFICATION
.EXCELLENT INTERLACING CONTROL .SPECIALPATENTED FRAME SYNCHRO DEVICE
FOR VCR OPERATION .FRAME SAW-TOOTH GENERATOR .FRAME PHASE MODULATOR FOR THYRISTOR
SMPS CONTROL .ERROR AMPLIFIER AND PHASE MODULATOR
.SYNCHRONIZATION WITH HORIZONTAL
DEFLECTION .SECURITY CIRCUIT AND START UP PROCESSOR.
This integrated circuit uses I2L bipolar technology
and combines analog signal processing with digital
Timing signals are obtainedfrom a voltage-controlled
oscillator (VCO) operatingat 500KHzby means
of a cheap ceramic resonator. This avoids the
frequency adjustment normally required with line
and frame oscillators.
A chain of dividers and appropriate logic circuitry
produce very accurately defined sampling pulses
and the necessary timing signals.
The principal functions implemented are :
- Horizontal scanning processor.
- Frame scanning processor. Two applications are
- D Class : Power stage using an external
- B Class : Powerstageusing an externalpower
amplifier with fly-back generator
such as the TDA8170.
- Secondary switch mode power regulation.
The SMPS output synchronize a primary I.C.
(TEA2260/61)at the mains part.
This concept allows ACTIVE STANDBY facilities.
- Dual phase-locked loop horizontal scanning.
- High performance frameand line synchronization
with interlacing control.
- Video identification circuit.
- Super sandcastle.
- AGC key pulse output.
- Automatic 50-60Hz standard identification.
- VCR input for PLL time constant and frame synchro
- Frame saw-tooth generator and phase modulator.
- Switchingmode regulated power supplycomprising
error amplifier and phase modulator.
- Security circuit and start-up processor.
The circuit is supplied in a 28 pin DIP case.
VCC = 12V.
Line synchronization separator is clamped to
black level of input video signal with synchronization
pulse bottom level measurement.
The synchronization pulses are divided centrally
between the black level and the synchronization
pulse bottom level, to improve performance on
video signals in noise conditions.
Frame synchronization is fully integrated (no external
The frame timing identification logic permits automatic
adaptation to 50 - 60Hz standards or non-interlaced
An automatic synchronization window width system
- fast frame capture (6.7ms wide window),
- good noise immunity (0.4ms narrow window).
The internal generator starts the discharge of the
saw-tooth generator capacitor so that it is not disturbed
by line fly back effects.
Thanks to the logic control, the beginning of the
charge phase does not depend on any disturbing
effect of the line fly-back.
A 32ms timing is automatically applied on standardized
transmissions, for perfect interlacing.
In VCR mode, the discharge time is controlled by
an internal monostable independent of the line
frequency and gives a direct frame synchronization.
The horizontalscanningfrequencyis obtainedfrom
the 500kHz VCO.
The circuit uses two phase-locked loops (PLL) :
the first one controls the frequency, the second one
controls the relative phase of the synchronization
and line fly-back signals.
The frequency PLL has two switched time constants
to provide :
- capture with a short time constant,
- good noise immunity after capture with a long
The output pulse has a constant duration of 26ms,
independent of VCC and any delay in switching off
the scanning transistor.
The horizontal synchronization signal is sampled
by a 2ms pulse within the synchronization pulse.
The signal is integrated by an external capacitor.
The identification function provides three different
- 0V : no video identification
- 6V : 60Hz video identification
- 12V : 50Hz video identification
This information may be used for timing research
in the case of frequency or voltage synthetizer type
receivers, and for audio muting.
Super Sandcastle with 3 levels : burst, line flyback,
In the event of vertical scanning failure, the frame
blanking level goes high to protect the tube.
Frame blanking time (start with reset of Frame
divider) is 24 lines.
This provides for continuous use of the short time
constant of the first phase-locked loop (frequency).
In VCR mode, the frame synchronization window widens out to a search window and there is no
delay of frame fly-back (direct synchronization).
FRAME SAW-TOOTH GENERATOR. The current
to charge the capacitoris automatically switched to
60Hz operation to maintain constant amplitude.
FRAME PHASE MODULATOR (WITH TWO DIFFERENTIAL
INPUTS). The output signal is a pulse
at the line frequency, pulse width modulatedby the
voltage at the differential pre-amplifier input.
This signal is used to control a thyristor which
provides the scanning current to the yoke. The
saw-tooth output is a low impedance,however, and
can therefore be used in class B operation with a
power amplifier circuit.
Switch Mode Power Supply (SMPS) Secondary
to Primary Regulation
This power supply uses a differential error amplifier
with an internal reference voltage of 1.26V and a
phase modulator operating at the line frequency.
The powertransistor is turnedoff bythe falling edge
of the horizontal saw-tooth.
The ”soft start” device imposes a very small conduction
angle on starting up, this angle progressively
increases to its nominal regulation value.
The maximum conductionangle may be monitored
by forcing a voltage on pin 15. This pin may also
be used for current limitation.
The outputpulse is sent to the primaryS.M.P.S. I.C.
(TEA2261) via a low cost synchro transformer.
Security Circuit and Start Up Processor
When the security input (pin 28) is at a voltage
exceeding 1.26V the three outputs are simultaneously
cut off until this voltagedrops below the 1.26V
threshold again. In this case the switch mode
power supply is restarted by the ”soft start” system.
If this cycle is repeated three times, the three
outputs are cut off definitively. To reset the safety
logic circuits, VCC must be zero volt.
This circuit eliminates the risk to switch off the TV
receiver in the event of a flash affecting the tube.
On starting up, the horizontal and vertical scanning
functions come into operation at VCC = 6V. The
power supply then comes into operation progressively.
On shutting down, the three functions are interrupted
simultaneously after the first line fly-back.
THOMSON TF5551 PG5 THOMSQUARE (ICC5) CHASSIS ICC5 (5116) APPLICATION INFORMATION ON FRAME
SCANNING IN SWITCHED MODE:
Fundamentals (see Figure 80)
The secondary winding of EHT transformer provides
the energy required by frame yoke.
The frame current modulation is achieved by
modulating the horizontal saw-tooth current and
subsequent integration by a ”L.C” network to reject
the horizontal frequency component.
The basic circuit is the phase comparator ”C1”
which compares the horizontal saw-tooth and the
output voltage of Error Amplifier ”A”.
The comparator output will go ”high” when the
horizontal saw-tooth voltage is higher than the ”A”
output voltage. Thus, the Pin 4 output signal is
switched in synchronization with the horizontal frequency
and the duty cycle is modulated at frame
A driver stage delivers the current required by the
external power switch.
The external thyristor provides for energy transfer
between transformer and frame yoke.
The thyristor will conduct during the last portion of
horizontal trace phase and for half of the horizontal
The inverse parallel-connected diode ”D” conducts
during the second portion of horizontal retrace and
at the beginning of horizontal trace phase.
Main advantages of this system are :
- Power thyristor soft ”turn-on”
Once the thyristor has been triggered, the current
gradually rises from 0 to IP, where IP will reach
the maximumvalue at the end of horizontal trace.
The slope current is determined by, the current
available through the secondary winding, the
yoke impedance and the ”L.C.” filter characteristics.
- Power thyristor soft ”turn-off”
The secondary output current begins decreasing
and falls to 0 at the middle of retrace. The thyristor
is thus automatically ”turned-off”.
- Excellent efficiency of power stage dueto very
low ”turn-on” and ”turn-off” switching losses.
During flyback, due to the loop time constant, the
frame yoke current cannot be locked onto the
reference saw-tooth. Thus the output of amplifier
”A” will remain high and the thyristor is blocked.
The scanning current will begin flowing through
diode ”D”. As a consequence, the capacitor ”C”
starts charging upto the flyback voltage.The thyristor
is triggeredas soon as the yoke current reaches
the maximum positive value.
TDA4443 MULTISTANDARD VIDEO IF AMPLIFIERDESCRIPTION
The TDA4443 is a Video IF amplifier with standard
switch for multistandard colour or monochromeTV
sets, and VTR’s.
SWITCHING OFF THE IF AMPLIFIER WHEN
OPERATING IN VTR MODE .DEMODULATION OF NEGATIVE OR POSITIVE
IF SIGNALS. THE OUTPUT REMAINS
ON THE SAME POLARITY IN EVERY CASE .IF AGC AUTOMATICALLY ADJUSTED TO
THE ACTUALSTANDARD .TWO AGC POSSIBILITIES FOR B/G MODE :
1. GATED AGC
2. UNGATED AGC ON SYNC. LEVEL AND
CONTROLLED DISCHARGE DEPENDENT
ON THE AVERAGE SIGNAL LEVEL FOR VTR
AND PERI TV APPLICATIONS
FOR STANDARD L : FAST AGC ON PEAK
WHITE BY CONTROLLED DISCHARGE .POSITIVE OR NEGATIVE GATING PULSE .EXTREMELY HIGH INPUT SENSITIVITY .LOW DIFFERENTIAL DISTORTION .CONSTANT INPUT IMPEDANCE .VERY HIGH SUPPLY VOLTAGE REJECTION .FEW EXTERNAL COMPONENTS .LOW IMPEDANCE VIDEO OUTPUT .SMALL TOLERANCES OF THE FIXED VIDEO
SIGNALAMPLITUDE .ADJUSTABLE, DELAYED AGC FOR PNP
This video IF processing circuit integrates the following
functional blocks : .Three symmetrical, very stable, gain controlled
wideband amplifier stages - without feedback
by a quasi-galvanic coupling. .Demodulator controlled by the picture carrier .Video output amplifier with high supply voltage
rejection .Polarity switch for the video output signal .AGC on peak white level .GatedAGC .Discharge control .Delayed tuner AGC .At VTR Reading mode the video output signal
is at ultra white level.
TDA4445A SOUND IF AMPLIFIER
.QUADRATURE INTERCARRIER DEMODULATOR
.VERY HIGH INPUT SENSITIVITY .GOODSIGNALTO NOISE RATIO .FAST AVERAGINGAGC .IF AMPLIFIER CAN BE SWITCHED OFF FOR
VTR MODE .GOODAM SUPPRESSION .OUTPUT SIGNAL STABILIZED AGAINST
SUPPLY VOLTAGE VARIATIONS .VERY FEW EXTERNAL COMPONENTS
Sound IF amplifier, with FM processing for quasi
parallel sound system.
Sound IF amplifier, with FM processing and AM
demodulator, for multi-standard sound TV appliances.
Bistandard applications (B/G and L)
No adjustment of the AM demodulator
This circuit includes the following functions : .Three symmetrical and gain controlled wide
band amplifier stages, which are extremely stable
by quasiDC coupling without feedback. .Averaging AGC with discharge control circuit .AGC voltage generator
Quasi parallel sound operation : .High phase accuracy of the carrier signal processing,
independentfrom AM .Linear quadrature demodulator .Sound-IF-amplifier stage with impedance converter
AM-Demodulation (only TDA4445B) : .Carrier controlled demodulator .Audio frequency stage with impedance converter
.Averaging low passAGC.
TDA4556 Multistandard decoder
The TDA4555 and TDA4556 are monolithic integrated
multistandard colour decoders for the PAL, SECAM,
NTSC 3,58 MHz and NTSC 4,43 MHz standards. The
difference between the TDA4555 and TDA4556 is the
polarity of the colour difference output signals (B-Y)
· Gain controlled chrominance amplifier for PAL, SECAM
· ACC rectifier circuits (PAL/NTSC, SECAM)
· Burst blanking (PAL) in front of 64 ms glass delay line
· Chrominance output stage for driving the 64 ms glass
delay line (PAL, SECAM)
· Limiter stages for direct and delayed SECAM signal
· SECAM permutator
· Flyback blanking incorporated in the two synchronous
demodulators (PAL, NTSC)
· PAL switch
· Internal PAL matrix
· Two quadrature demodulators with external reference
tuned circuits (SECAM)
· Internal filtering of residual carrier
· De-emphasis (SECAM)
· Insertion of reference voltages as achromatic value
(SECAM) in the (B-Y) and (R-Y) colour difference output
· Automatic standard recognition by sequential inquiry
· Delay for colour-on and scanning-on
· Reliable SECAM identification by PAL priority circuit
· Forced switch-on of a standard
· Four switching voltages for chrominance filters, traps
· Two identification circuits for PAL/SECAM (H/2) and
· PAL/SECAM flip-flop
· SECAM identification mode switch (horizontal, vertical
or combined horizontal and vertical)
· Crystal oscillator with divider stages and PLL circuitry
(PAL, NTSC) for double colour subcarrier frequency
· HUE control (NTSC)
· Service switch.
THOMSON TF5551 PG5 THOMSQUARE (ICC5) CHASSIS ICC5 (5116) U4606 - TEA5040 (TELEFUNKEN) WIDE BAND VIDEO PROCESSOR
The U4647 - TEA5040S is a serial bus-controlled videoprocessing
device which integrates a complex architecture
fulfilling multiple functions.
.DIGITAL CONTROL OF BRIGHTNESS,
SATURATION AND CONTRAST ON TV SIGNALS
AND R, G, B INTERNAL OR EXTERNAL
SOURCES .BUS DRIVE OF SWITCHING FUNCTIONS .DEMATRIXING OF R, G, B SIGNALS FROM
Y, R-Y, B-Y, TV MODE INPUTS .MATRIXING OF R, G, B SOURCES INTO
Y, R-Y, B-Y SIGNALS .AUTOMATIC DRIVE AND CUT-OFF CONTROLS
BY DIGITAL PROCESSING DURING
FRAME RETRACE .PEAK ANDAVERAGE BEAM CURRENT LIMITATION
.ON-CHIP SWITCHING FOR R, G, B INPUT
SELECTION .ON-CHIP INSERTION OF INTERNAL OR EXTERNAL
R, G, B SOURCES
An automatic contrast control circuit in a color television receiver for stabilizing the average DC level of the luminance information at a desired level and preventing focus blooming. The control circuitry, which is suitable for fabrication as a monolithic integrated circuit, contemplates the provision of a gain-controlled luminance amplifier stage for driving an image reproducer with luminance information having a stabilized black level. An average detector coupled to the amplifier stage output develops a control signal representative of the average DC level of the luminance information and applies it to the amplifier stage, varying its gain inversely with changes in the average luminance level. A peak limiter circuit is also provided for modifying the control signal to reduce the amplifier stage's gain whenever an AC brightness component comprising the luminance information exceeds a defined threshold level, regardless of the average DC level of the luminance information.
1. In a television receiver having a luminance processing channel for translating instantaneous luminance signals derived from received broadcast transmissions to an image reproducer, said luminance signals including black level reference information, an automatic contrast control circuit comprising in combination:
2. An automatic contrast control circuit in accordance with claim 1, wherein adjustable level shifting means are interposed between said amplifier stage and said average detector means, said adjustable level shifting means providing a contrast control for manually varying the average DC level of said luminance signals.
3. An automatic contrast control circuit in accordance with claim 1, wherein said average detector means includes a capacitor having an output terminal coupled to said amplifier stage and a second terminal coupled to a plane of reference potential, said capacitor being charged by luminance signals from said amplifier stage and developing control signals representative of the average DC level of said luminance signals.
4. An automatic contrast control circuit in accordance with claim 3, wherein said control signals with respect to a plane of reference potential are equal to the potential at which black level is stabilized minus the potential drop between black level and the average DC level of said luminance information, said control signal increasing with respect to said plane of reference potential responsive to decreasing average DC levels of said luminance signals and decreasing responsive to increasing average DC levels.
5. An automatic contrast control circuit in accordance with claim 3, wherein said peak detector means includes a semi-conductor arrangement for providing said capacitor with a low impedance discharge path whenever said brightness components exceed a predetermined threshold level, the impedance of said discharge path being dependent on the amplitude of said brightness components and the discharge interval of said semiconductor arrangement being the time period during which said brightness components exceed said threshold level, said semiconductor arrangement further decreasing said control signals with respect to said plane of reference potential irrespective of the average DC level of said luminance signals.
6. An automatic contrast control circuit in accordance with claim 5, wherein said semiconductor arrangement comprises first and second transistors, said luminance signals from said amplifier stage being coupled to the input base electrode of said first transistor, said first transistor further having an emitter electrode coupled to said capacitor output terminal and a collector electrode coupled to the base electrode of said second transistor, said second transistor having a collector electrode coupled to said capacitor output terminal and an emitter electrode coupled to said plane of reference potential, said semiconductor arrangement being conductive to provide said capacitor with a low impedance discharge path whenever said brightness components exceed the base-emitter junction breakdown voltage of said first transistor.
7. An automatic contrast control circuit in accordance with claim 6, wherein said gain-controlled luminance amplifier stage includes a pair of transistors arranged in a differential amplifier configuration, the gain of which is dependent on the bias applied to the base electrodes of said transistors.
8. An automatic contrast control circuit in accordance with claim 7, wherein inverter means invert and couple said control signals to said base electrodes in said amplifier stage, the inverted control signals increasing the gain of said amplifier stage whenever the average DC level of said luminance signals decreases and decreasing the gain of said amplifier stage whenever the average DC level of said luminance information increases or whenever said brightness components exceed said threshold level.
9. An automatic contrast control circuit in accordance with claim 3, wherein said beam current limiter means provide a low impedance discharge path for said capacitor whenever the beam current exceeds a predetermined level.
10. An automatic contrast control system in accordance with claim 9, wherein said beam current limiter means monitors pulses from a voltage multiplier high-voltage system, said pulses being proportional to the beam current generated during the previous horizontal scan line.
11. An automatic contrast control circuit in accordance with claim 10, wherein said beam current limiter means comprises a transistor having a base electrode coupled to said voltage multiplier high-voltage system, an emitter electrode coupled to a plane of reference potential and a collector electrode coupled to said capacitor, said transistor providing a low impedance discharge path whenever said pulses exceed the base-emitter junction breakdown voltage of said transistor.
This invention relates in general to control circuitry for color television receivers and more particularly to an automatic contrast control circuit incorporated in the luminance processing channel. In accordance therewith, a variable DC control signal is derived from the luminance signal information as a function of the average luminance level. The DC control signal is applied to a gain-controlled amplifier stage in the luminance channel, varying its gain and thereby insuring that excessive beam currents will not be generated due to high average luminance levels. Conversely, the circuit is effective to increase the gain of the amplifier stage when under-modulated signals are received thereby providing the desired contrast level. When the white content of the instantaneous received signal exceeds a predetermined level, however, the DC control signal is modified to reflect the excessive white content even though the average luminance level may be low. Accordingly, the amplifier stage's gain is reduced to prevent defocusing.
In color television receivers, the various elemental areas of differing brightness levels, or shades, in the televised image correspond to the amplitude levels of the instantaneous brightness components of the luminance signals which, together with the chrominance signal, reproduce the transmitted picture information on the image display tube. The intensity of the electron beams developed in the receiver's image display tube are varied, for the most part, according to the detected amplitude levels of the instantaneous luminance signals. Accordingly, progressively higher amplitude levels generate higher intensity electron beams and, consequently, progressively lighter shades. In addition, suitable viewer-adjustable controls are customarily provided in the television receiver whereby a particularized contrast and brightness setting may be selected according to viewer preference.
It is desirable that the level of the luminance signal component corresponding to black in the televised image be maintained at the cut-off of the image reproducer. But even in those instances where there is a measure of DC coupling, the DC components of the luminance signal coupled from the video detector to the luminance channel may be degraded or otherwise restricted due to the nature of the processing circuitry as well as to other factors. Moreover, the luminance processing channel itself may well permit a degradation or undesirable shift in the desired DC characteristics. The result is that the DC level in the processed luminance signal is not properly maintained, such that, upon application to the image display tube, the black level is shifted to some undesirable reference. This leads to less than faithful half-tone reproduction on the screen of the image display tube. Gray tones can be lost simply because they are beyond the cut-off of the display tube. In other instances, blacks may appear as grays on the image display tube screen.
Thus, it is desirable to make provision for the maintenance of black level in the televised image at some stabilized reference. Various systems are of course known in the art for accomplishing this objective and take various forms and configurations. For example, an arrangement commonly known as a DC restorer circuit which includes a clamping device may be employed. However, when the black level is effectively stabilized at the image reproducer's cut-off bias point, the average level of the luminance signal information may reach the point where excessive average beam currents capable of severely damaging the image reproducer are generated. In addition, the high voltage power supply during instances of high beam current may be incapable of delivering the required beam current. Such overloading reduces the power supply output voltage and results in undesirable "focus blooming." That is, there will be a loss of brightness, reduction of horizontal widths and severe defocusing of the reproduced image. The problem in this regard has been further compounded by the "new generation" high-brightness cathode-ray tubes which require higher beam currents in order to illuminate the tube to its fullest capability during high-modulation (white) scenes. In view of the added demands on the high voltage power supply and the danger of damaging the image display tube, some method for effectively limiting the beam current is required.
Accordingly, automatic contrast control systems have been developed which reduce the gain of the luminance amplifier stage to prevent the generation of excessive beam currents or increase the gain when under-modulated signals are received. Most of these prior art automatic contrast control systems, however, measure only the average level of the luminance signals to derive the control signal utilized to vary the gain of the luminance amplifier. Consequently, when all or a major portion of the luminance signal's white content is of a high amplitude level and is concentrated on a very small portion of the image reproducer's screen, the control signal derived from the average luminance level is low, permitting the luminance amplifier stage to operate at nearly maximum gain. By concentrating the high-amplitude white content into a small area of the screen, the image display tube is likely to be overdriven during that period of time and "focus blooming" will result. Some automatic contrast systems, on the other hand, derive a control signal based on the peak amplitudes of the instantaneous luminance signals without regard to the average luminance level. Thus, while preventing blooming on high-amplitude white content, such systems are susceptible to luminance signals which have a dangerously high average level, but do not have any peak white signal content of a level where the system would take corrective action.
OBJECTS OF THE INVENTION
Accordingly, it is an object of the present invention to provide a color television receiver having black level stabilization with a new and improved automatic contrast control circuit which effectively overcomes the aforenoted disadvantages and deficiencies of prior circuits.
A further object of the invention is to provide an improved automatic contrast control circuit which develops control signals effectively varying the gain of a luminance amplifier stage to maintain an optimum contrast, while preventing the generation of excessive beam currents in the cathode-ray tube.
A more particular object of the invention is to provide an improved automatic contrast control circuit for continuously monitoring the average (DC) level of the luminance signal information and providing a control signal representative thereof to vary the gain of a luminance amplifier stage while remaining sensitive to the amplitude levels of brightness components exceeding a threshold level and modifying the control signal in accordance therewith.
Another object of the invention is to provide an improved automatic contrast control circuit which increases the gain of a luminance amplifier stage during reception of undermodulated luminance signals.
A further object of the present invention is to provide an automatic contrast control circuit of the foregoing type for deriving a variable DC control potential from applied luminance signals which, upon application to the luminance channel, adjusts the gain of a luminance amplifier stage in accordance with the varying luminance signal requirements.
Still another object of the invention is to provide a luminance processing channel including automatic contrast control circuitry which may be fabricated as a monolithic integrated circuit to provide an output luminance signal having stabilized black level and optimum contrast without producing excessive beam currents.
SUMMARY OF THE INVENTION
In accordance with the present invention, an improved automatic contrast control circuit is provided for varying the gain of an amplifier stage in the luminance processing channel of a color television receiver whenever the average DC level of the input luminance information varies from a desired level, or whenever the peak amplitudes of the AC brightness components of the luminance information exceed a predetermined threshhold level. In a preferred embodiment, the automatic contrast control circuit includes a gain-controlled luminance amplifier stage in a luminance processing channel for translating instantaneous luminance signals derived from received broadcast transmissions to an image reproducer. The amplified luminance signals found at the output of the amplifier stage have a stabilized black level. There are also provided detector means coupled to the amplifier output for developing control signals that are representative of the average DC level of the instantaneous luminance signals. The control signals are then applied to the gain-controlled amplifier stage to vary its gain inversely with changes in the average luminance level. Finally, peak limiter means are coupled between the amplifier output and the detector means to modify the control signals whenever the instantaneous luminance signals exceed a threshhold level. The modified control signals are similarly utilized to effect inverse gain variations in the gain-controlled amplifier stage regardless of the average level of the luminance signals.
This integrated circuit incorporates the following
- a synchro and two video inputs
- a fixed video output
- a switchable video output
- normal Y, R-Y, B-Y TV mode inputs
- double set of R, G, B inputs
- brightness, contrast and saturation controls as
wellon aR,G, B picture ason a normalTVpicture
- digital control inputs by means of serial bus
- peak beam current limitation
- average beam current limitation
- automaticdrive and cut-off controls
Block Diagram Description
A 3 lines bus (clock, data, enable) delivered by the
microcontroller of the TV-set enters the videoprocessor
integrated circuit (pins 13-14-15). A control
system acts in such a way that only a 9-bit word is
taken intoaccount by the videoprocessor.Six of the
bits carry the data, the remaining three carry the
address of the subsystem.
A demultiplexer directs the data towards latches
which drive the appropriate control. More detailed
information about serial bus operation is given in
the following chapter.
The video switch has three inputs :
- an internal video input (pin 39),
- an external video input (pin 37),
- a synchro input (pin 41),
and two outputs :
- an internal video output (pin 40),
- a switchable video output (pin 42)
The 1Vpp composite video signal applied to the
internal video input is multiplied by two and then
appears as a 2Vpp low impedance composite
video signal at the output. This signal is used to
deliver a 1Vpp/75W composite video signal to the
The switchable video output canbe any of the three
inputs.When the Int/Ext one active bit word is high
(address number 5), the internal video input is
selected. If not, either a regeneratedsynchro pulse
or the external video signal is directed towards this
output depending on the level of the Sync/Async
one active bit word (address number 4). As this
output is to be connected to the synchro integrated
circuit, RGB information derived from an external
source via the Peri-TV plug canbedisplayed on the
screen, the synchronization of the TV-set being
then made with an external video signal.
When RGB information is derived from a source
integrated in the TV-set, a teletext decoder for
example, the synchronization can be made either
on the internal video input (in case of synchronous
data) or on the synchro input (in case of asynchronous
R, G, B Inputs
There are two sets of R, G, B inputs : one is to be
connected to the peri-TV plug (Ext R, G, B), the
second one to receive the information derived from
the TV-set itself (Int R, G, B).
In order to have a saturation control on a picture
coming from the R, G, B inputs too, it is necessary
to getR-Y, B-Y and Y signals from R, G, B information
: this is performed on the first matrix that
receives the three 0.9Vp (100% white) R, G, B
signals and delivers the corresponding Y, R-Y, B-Y
signals. These ones are multiplied by 1.4 in order
to make the R-Y and B-Y signals compatible with
the R-Y and B-Y TV mode inputs. The desired R,
G, B inputs are selected by means of 3 switches
controlled by the two fast blanking signal inputs. A
high level on FB external pin selects the external
RGB sources. The three selected inputs are
clamped in order to give the required DC level at
the output of this firstmatrix. Thethree not selected
inputs are clamped on a fixed DC level.
Y, R-Y, B-Y Inputs
The 2Vpp composite video signal appearing at the
switchable output of the video switch (pin 42) is
driven through the subcarrier trap and the luminance
delay line with a 6 dB attenuation to the Y
input (1Vpp ; pin 12). In order to make this 1Vpp
(synchro to white) Y signal compatible with the
1Vpp (black to white) Y signal delivered by the first
matrix, it is necessary to multiply it by a coefficient
The four brightness, contrastand saturationcontrol
functions are direct digitally controlled without using
The contrast control of the Y channel is obtained
by means of a digital potentiometer which is an
attenuator including several switchable cells directly
controlled by a 5 active bit word (address
number 1). The brightness control is also made by
a digital potentiometer (5 active bit word, address
number 0). Since a + 3dB contrast capability is
required, the Y signal value could be up to 0.7Vpp
nominal. For both functions, the control characteristics
In each R-Y and B-Y channel, a six-cell digital
attenuator is directly controlled by a 6 active bit
word (address number 6 and 7). The tracking
needed to keep the saturation constant when
changing the contrast has to be done externally by
the microcontroller. Furthermore, colour can be
disabledby blankingR-Y andB-Ysignals using one
active bit word (address number 2) to drive the
one-chip colour ON/OFF switch.
Second Matrix, Clamp, Peak Clipping, Blanking
The second matrix receives the Y, R-Y and B-Y
signals and delivers the corresponding R, G, B
signals. As it is required to have the capability of +
6dB saturation, an internal gain of 2 is applied on
both R-Y and B-Y signals.
A low clipping level is included in order to ensure a
correct blanking during the line and frame retraces.
Ahigh clipping level ensures thepeakbeamcurrent
limitation. These limitations are correct only if the
DC bias of the three R, G, B signals are precise
enough. Therefore a clamp has been added in
each channel in order to compensate for the inaccuracy
of the matrix.
Sandcastle Detector And Counter
The three level supersandcastle is used in the
circuit to deliver the burst pulse (CLP), the horizontal
pulse (HP), and the composite vertical and
horizontal blanking pulse (BLI). This last one is
regenerated in the counter which delivers a new
composite pulse (BL) in which the vertical part lasts
23 lines when the vertical part of the supersandcastle
lasts more than 11 lines.
The TEA5040S cannot work properly if this minimum
duration of 11 lines is not ensured.
The counterdelivers different pulses neededcircuit
and especially the line pulses 17 to 23 used in the
automatic drive and cut-off control system.
Automatic Drive And Cut-off Control System
Cut-off and drive adjustments are no longer required
with this integrated circuit as it has a sample
and hold feedback loop incorporating the final
stages of the TV-set. This system works in a sequentialmode.
For this purpose, special pulses are
inserted in G, R and B channels. During the lines
17, 18 and 19, a ”drive pulse” is inserted respectively
in the green, red and blue channels. The line
20 is blanked on the three channels. During the
lines 21, 22 and 23, a ”quasi cut-off pulse” is
inserted respectively in the green, red and blue
The resulting signal is then applied to the input of
a voltage controlled amplifier. In the final stages of
the TV-set, the current flowing in each green, red
and blue cathode is measured and sent to the
videoprocessorby a current source.
The three currents are added together in a resistor
matrix which can be programmed to set the ratio
between the three currents in order to get the
appropriate colour temperature. The output of the
matrix forms a high impedance voltage source
which is connectedto the integratedcircuit (pin 34).
Same measurement range between drive and cutoff
is achieved by internally grounding an external
low impedance resistor during lines 17, 18 and 19.
This is due to the fact that the drive currents are
about one hundred times higher than the cut-off
and leakage currents.
Each voltage appearing sequentially on the wire
pin 34 is then a function of specific cathode current
- When a current due to a drive pulse occurs, the
voltage appearing on the pin 34 is compared
within the IC with an internal reference, and the
result of the comparison charges or discharges
an external appropriate drive capacitor which
stores the value during the frame. This voltage is
applied to a voltage controlled amplifier and the
system works in such a waythat the pulse current
drive derived from the cathode is kept constant.
- During the line 20, the three guns of the picture
tube are blanked. The leakagecurrent flowing out
of the final stages is transformed into a voltage which is stored by an external leakage capacitor
to be used later as a reference for the cut-off
- When a current due to a cut-off pulse occurs, the
voltage appearing on the pin 34 is compared
within the ICto the voltagepresenton the leakage
memory. Anappropriate externalcapacitor is then
charged or discharged in such a way that the
difference between each measured current and
the leakage current is kept constant, and thus the
quasi cut-off current is kept constant.
AverageBeam Current Limitation
The total current of the three guns is integrated by
means of an internal resistor and an external capacitor
(pin 36) and thencompared with a programmable
voltage reference(pin 38). When 70% of the
maximum permitted beam current is reached, the
drive gain begins to be reduced ; to do so, the
amplitude of the inserted pulse is increased.
In order to keep enough contrast, the maximum
drive reduction is limited to 6dB. If it is not sufficient,
the brightness is suppressed.
SPECIFICATION FOR THE THOMSON BI-DIRECTIONAL
This is a bi-directional 3-wire (ENABLE, CLOCK,
DATA) serial bus. The DATA line transmission is
bi-directional whereas ENABLE and CLOCK lines
are only microprocessor controlled. The ENABLE
and CLOCK lines are only driven by the microcomputer.
THOMSON CHASSIS ICC5 Switched mode power supply transformer
A switched mode power supply transformer, particularly for a television receiver, including a primary winding and a secondary winding with the primary winding and the secondary winding each being subdivided into a plurality of respective partial windings. The partial windings of the primary lie in a first group of chambers and the partial windings of the secondary lie in a second group of chambers of a chamber coil body, and the chambers of both groups are nested or interleaved with one another.
1. A switched mode power supply transformer, particularly for a television receiver, comprising in combination:
a primary winding and a secondary winding, with said primary winding being subdivided into three partial windings and said secondary winding being subdivided into two partial windings;
a chamber coil body having a plurality of chambers;
said partial windings of said primary winding being disposed only in a first group of said chambers, and said partial windings of said secondary winding being disposed only in a second group of said chambers, with each of said partial windings being disposed in a respective one of said chambers;
said chambers of said first group being interleaved with said chambers of said second group such that they alternate in sequence with said primary partial windings and said secondary partial windings being alternatingly disposed in five successive said chambers, so as to generate the major operating voltage at said secondary winding;
an additional secondary winding for generating a further operating voltage, said additional secondary winding likewise being subdivided into a plurality of partial windings; and,
said partial windings of said additional secondary winding are disposed only in respective said chambers of said second group below any of said partial windings of said secondary winding.
2. A transformer as defined in claim 1 wherein the total number of said chambers is six.
3. A transformer as defined in claim 1 wherein the width of the narrowest of said chambers is approximately 1 mm.
4. A transformer as defined in claim 1 or 2 wherein the widths of said chambers are different.
5. A transformer as defined in claim 1 or 2 wherein the total width of all of said chambers is only approximately 20 mm, whereby a flat and optimally coupled transformer is realized.
6. A transformer as defined in claim 1 wherein said additional secondary winding provides an operating voltage for a load which has a fluctuating current input.
7. A transformer as defined in claim 1 wherein said partial windings of said additional secondary winding are connected in parallel.
8. A transformer as defined in claim 1 wherein said partial windings of said primary winding are connected in series.
9. A transformer as defined in claim 1 or 8 wherein said partial windings of said secondary winding are connected in series.
10. A transformer as defined in claim 1 further comprising a plurality of auxiliary primary windings disposed in one chamber of said first group which is disposed in approximately the center of said first group and above the said partial winding of said primary winding disposed in said one chamber of said first group.
11. A transformer as defined in claim 1 wherein all of said partial winding disposed in said chambers of both said groups are wound with wire having the same diameter.
12. A switched mode power supply transformer as defined in claim 1 or 10 wherein: said coil body has six of of said chambers; said additional secondary winding is subdivided into three said partial windings; and two of said partial windings of said additional secondary winding are disposed below respective ones of said partial windings of said secondary winding and the third said partial winding of said additional secondary winding is disposed in the sixth said chamber.
13. A switched mode power supply transformer as defined in claim 10 further comprising at least one further secondary winding disposed in one of said chambers of said second group above any partial secondary winding present in said one of said chambers.
14. A switched mode power supply transformer, particularly for a television receiver, comprising in combination:
a primary winding and a secondary winding, with said primary winding and said secondary winding each being subdivided into a plurality of partial windings;
a chamber coil body having a plurality of chambers;
said partial windings of said primary winding being disposed only in a first group of said chambers, and said partial windings of said secondary winding being disposed only in a second group of said chambers with each of said partial windings being disposed in a respective one of said chambers;
said chambers of said first group being interleaved with said chambers of said second group such that said primary partial windings and said secondary partial windings are alternatingly disposed in successive said chambers, so as to generate the major operating voltage at said secondary winding;
an additional secondary winding for generating a further operating voltage, said additional secondary winding likewise being subdivided into a plurality of partial windings, and said partial windings of said additional secondary winding are disposed only in respective said chambers of said second group below any of said partial windings of said secondary winding.
15. A switched mode power supply transformer as defined in claim 1 or 14 wherein each of said partial windings of said primary winding contains the same number of turns and each of said partial windings of said secondary winding contains the same number of turns.
The present invention relates to a switched mode power supply transformer, particularly for a television receiver.
In communications transmissions devices, particularly in television receivers, it is known to effect the desired dc decoupling from the mains by means of so-called switched mode power supply transformers. Such switched mode power supply transformers are substantially smaller and lighter in weight than a mains transformer for the same power operating at 50 Hz, because they operate at a significantly higher frequency of about 20-30 kHz. Such a switched mode power supply transformer (hereinafter called SMPS transformer) generally includes a primary side with a primary winding serving as the operating winding for the switch and further additional auxiliary windings, as well as a secondary side with a secondary winding for generating the essential operating voltage and possibly further additional windings for generating further operating voltages of different magnitude and polarity. The secondary and primary are insulated from one another as prescribed by VDE and have the necessary dielectric strength so that there is no danger of contact between voltage carrying parts on the secondary. A switched mode power supply (SMPS) circuit for a tv-receiver is described in U.S. Pat. No. 3,967,182, issued June 29, 1976.
A further requirement placed on such an SMPS transformer is that the stray inductance at least of the primary winding and of the secondary winding should be as small as possible. With too high a stray inductance, a transient behavior may develop during the switching operation which would not assure optimum switch operation of the switching transistor connected to the primary winding and would endanger this transistor by taking on too much power. Moreover, an increased stray inductance undesirably increases the internal resistance of the voltage sources for the individual operating voltages.
It is known to design the windings for such transformers as layered windings. Such layered windings, however, contain feathered intermediate foil layers and, after manufacture, generally require that the coil or the complete transformer be encased in order to insure VDE safety. Use as a chamber winding in television receivers presently does not take place because of the problems to be discussed below. A chamber winding would have the particular advantage that it could be wound more easily and economically by automatic machines. when using a chamber winding for a switched mode power supply, the detailed insulation between the primary and the secondary would be realized initially by two chambers with one of these chambers being filled only with the windings of the primary and the other of these chambers being filled only with the windings of the secondary. However, with such an arrangement there would exist only slight coupling between the primary and the secondary and thus an undesirably high stray inductance. If, on the other hand, the number of chambers were selected to be substantially larger, the transformer becomes more expensive and unnecessarily large. Moreover, a larger core would be required. Consequently, in the past, no television receiver has been introduced that included an SMPS transformer.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide an SMPS transformer designed in the chamber wound technique which permits economical automatic winding, i.e. can be wound with but a single type of wire, has a structure which is spatially narrow and as flat as possible, provides the required insulation between the primary and secondary windings, and has a low stray inductance. The transformer should not be encased or saturated and nevertheless should produce no interfering noise during operation. The transformer should be able to be held in a circuit board without mechanical aids merely by its connecting terminals which are soldered to the circuit board.
The above object is basically achieved according to the present invention in that the transformer for a switched mode power supply, particularly for a television receiver, comprises: a primary winding and a secondary winding with the primary and secondary windings each being subdivided into a plurality of partial windings; and a chamber coil body with a plurality of chambers; and wherein the partial windings of the primary winding are disposed in a first group of chambers of the coil body, the partial windings of the secondary winding are disposed in a second group of chambers of the coil body, and the chambers of the first and second groups are interleaved.
Due to the fact that the individual windings or partial windings of the primary are disposed only in chambers of the first group and the windings or partial windings of the secondary are disposed only in chambers of the second group, i.e. primary and secondary are distributed to separate chambers, the necessary dielectric strength between primary and secondary is assured. By dividing each of the primary and secondary windings to a respective plurality or group of chambers and, due to the interleaved or nested arrangement of the chambers of the primary and the secondary, the desired fixed coupling between primary and secondary, and thus the desired low stray inductance at the primary and secondary, are realized. It has been found that a total number of chambers in the order of magnitude of six constitutes an economically favorable solution. With a smaller number of chambers, the coupling between primary and secondary is reduced. With a larger number of chambers, however, either the individual chambers become too small or the entire transformer, and particularly the core, become too large.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit diagram for a preferred embodiment of a switched mode power supply transformer according to the invention.
FIG. 2 is a schematic partial sectional view showing the distribution of the individual windings of FIG. 1 to different chambers according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a transformer intended for a switched mode power supply for a television receiver with a power output between 40 and 150 watts. The transformer includes a primary side P and a secondary side S which, while maintaining the required dielectric strength of, for example, 10,000 V, are galvanically decoupled or separated from one another. The primary side P includes a primary winding 1 which, as the operating winding, will lie in the collector circuit of a switching transistor switched at about 20-30 kHz. The primary winding 1 is divided into three partial windings 1a, 1b and 1c which are connected in series. When utilized in a television receiver, the beginning of partial winding 1a and the end of partial winding 1c are connected into the collector circuit of the switching transistor, while the taps between the partial windings 1a-1b and 1b-1c are not utilized, but rather form supporting points for the connection of the terminals of the partial windings. The primary side P also includes an additional winding 3 which feeds the feedback path with which the primary winding 1a-1c is designed as a self-resonant circuit. Moreover, the primary side P includes an additional winding 4 for regulating the moment of current flow in the switching transistor in the sense of stabilizing the amplitude of the output voltages on the secondary side S.
The secondary side S initially includes the secondary winding 2 from which is obtained, via a rectifier circuit (not shown), the main operating voltage U1. The secondary winding 2 is divided into two series connected partial windings 2a and 2b. Additionally, the secondary winding S includes a winding 5 for generating an operating voltage for the video amplifier and a further winding 6 for generating the operating voltage for the vertical deflection stage of a television receiver. Moreover, an additional secondary winding 7 is provided from which, after rectification, the operating voltage or the audio output stage of the receiver is obtained. Winding 7 comprises three partial windings 7a, 7b, 7c which are connected in parallel. The audio output stage of a television receiver has a greatly fluctuating current input between 50 mA and 1000 mA so that the load of the secondary side S varies considerably. This variation in load may effect an undesirable change in the operating voltage U1 which also influences the horizontal deflection amplitude. This undesirable dependency can be reduced in that the coupling between winding 7 and winding 4 is dimensioned greater, for regulating purposes, than the coupling between winding 2 and winding 4. This solution is described in greater detail in Federal Republic of Germany Offenlegungsschrift (laid open application) DE-OS No. 2,749,847 of May 10, 1979. This increased coupling between windings 7 and 4 is realized in the present case by the three parallel connected windings 7a, 7b, 7c. Finally, the secondary S includes a further winding 8 which serves to generate, after rectification, a negative operating voltage of -30 V.
FIG. 2 shows one half of the chamber coil body 9 for the individual windings of FIG. 1, with the body 9 including a total of six chambers 10. The size and particularly the widths of the individual chambers 10 can vary with respect to one another and the widths may all be different. Preferably, the width of the narrowest chamber 10 is about 1 mm and the total width of all six chambers is only approximately 20 mm so as to realize a flat and optimally coupled transformer.
As shown, one third of the primary winding 1, in the form of respective partial windings 1a, 1b and 1c, is distributed to each of the first, third and fifth chambers 10 of the coil body 9. The additional primary windings 3 and 4 are disposed in the third chamber 10 above the partial winding 1b. One half of the secondary winding 2, in the form of respective partial windings 2a, 2b, is distributed to each of the second and fourth chambers 10 of the coil body 9. The three partial windings 7a, 7b and 7c of the additional secondary winding 7 for the audio output stage are distributed to the second, fourth and sixth chambers 10, respectively, with the partial windings 7a-7c being disposed closest to the longitudinal axis of the coil body 9 and thus below any partial secondary winding 2a, 2b or other secondary winding which may be located in the same chamber. That is, the partial windings 7a and 7b are disposed below the partial windings 2a and 2b, respectively, in the respective second and fourth chambers 10, and below the additional secondary windings 5 and 8 in the sixth chamber 10. Further winding 6 is disposed above partial secondary winding 2b.
As can be seen in FIG. 2, the chambers 10 contain alternatingly only windings or partial windings of the primary side P or of the secondary side S. The illustrated nesting or interleaving of the windings, i.e. the alternating arrangement of windings of the primary side P and of the secondary side S in successive chambers 10, assures the desired close coupling between the primary side P and the secondary side S. The arrangement of the windings 3, 4 in approximately the center of the coil body 9 above partial winding 1b assures the desired close coupling between the windings 3, 4 with the other windings.
In an embodiment of the transformer shown in FIGS. 1 and 2 which was successfully tested in practice, the individual windings were all wound with the same diameter wire and contained the following numbers of turns:
|Winding No. Number of Turns|
It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.