SABA ULTRACOLOR T5666 Telecommander CM CHASSIS CM110 75 204 000 30 UNITS VIEW.

- Line deflection UNIT: Horiz-Ablenk-Modul 75 204 200 32 d

- Frame deflection Unit: Vertikal-Ablenk-Modul 75 204 210 00 with MJ900 MJ1000
(Motorola)

- E/W Correction Unit: Ost-West-Modul 75 204 214 00

- Convergence unit

- RGB Ampl Unit: Rgb-Endst-Modul M 75 204 010 00 TBA530

- Tymer Clock feature Unit: Uhr/Einblend-Modul 75 209 016 00 AY-5-1232 + AY-5-8320

- Power Supply Unit: Schalt NetzModul M 75 204 007 00

- IF Det /Ampl Unit: ZF/AFC Modul 75 209 401 00 TDA2541

- Luminance / Chrominance Unit : Pal DecoderModul M 75 204 011 00 TDA2522 + TDA2560

- Sound Amplifier Unit: Ton Modul 75 204 012 00 TDA1035 (ITT)

- Synchronization Unit: Synchronisier Modul M 75 204 212 00 TDA2590 (PHILIPS)








TDA2522 PAL TV CHROMA DEMODULATOR COMBINATION
FAIRCHILD LINEAR INTEGRATED CIRCUIT
GENERAL DESCRIPTION- The TDA2522 is a monolithic integrated circuit designed as
a synchronous demodulator for PAL color television receivers. It includes an 8,8 MHz
oscillator and divider to generate two 4.4 MHz reference signals and provides color difference outputs.
PACKAGE OUTLINE 9B

The TDA2522 is Intended to Interface directly with the TDA2560 with a minimum oF external components. The TDA2530 may be added if RGB drive is required. The TDA2522
is constructed using the Fairchild Planar* process.





TDA2560 LUMINANCE AND CHROMINANCE CONTROL COMBINATION
The TDA2560 is a monolithic integrated circuit for use in decoding systems of COLOR
television receivers. The circuit consists of a luminance and chrominance amplifier.
The luminance amplifier has a low input impedance so that matching of the luminance
delay line is very easy.
It also incorporates the following functions:
- d.c. contrast control;
- d.c. brightness control;
- black level clamp;
- blanking;
- additional video output with positive-going sync.
The chrominance amplifier comprises:
- gain controlled amplifier;
- chrominance gain control tracked with contrast control;
- separate d.c. saturation control:
- combined chroma and burst output, burst signal amplitude not affected by contrast and
saturation control;
- the delay line can be driven directly ‘by the IC.

APPLICATION INFORMATION (continued)
The function is quoted against the corresponding pin number
Balanced chrominance input signal (in conjunction with pin 2)
This is derived from the chrominance signal bandpass filter, designed to provide a
push-pull input. A signal amplitude of at least 4 mV peak-to-peak is required
between pins l and 2. The chrominance amplifier is stabilized by an external feedback
loop from the output (pin 6) to the input (pins I and 2). The required level at pins l
and 2 will be 3 V.
All figures for the chrominance signals are based on a colour bar signal with 75%
saturation: i.e. burst-to-chrominance ratio of input signal is 1 1 2.
Chrominance signal input (see pin 1)
A. C.C. input
A negative-going potential, starting at +l,2 V, gives a 40 dB range of a. c. c.
Maximum gain reduction is achieved at an input voltage of 500 mV.
Chrominance saturation control
A control range of +6 dB to >-14 dB is provided over a range of d. c. potential on
pin 4 from +2 to +4 V. The saturation control is a linear function of the control
voltage.
Negative supply (earth)
Chro minance signal output
For nominal settings of saturation and contrast controls (max. -6 dB for saturation,
and max. -3 dB for contrast) both the chroma' and burst are available at this pin, and
in the same ratio as at the input pins 1 and 2. The burst signal is not affected by the
saturation and contrast controls. The a.c. c. circuit of the TDA2522 will hold
constant the colour burst amplitude at the input of the TDA2522. As the PAL delay
line is situated here between the TDA256O and TDA2522 there may be some variation
of the nominal 1 V peak-to-peak burst output of the TDA2560, according to the
tolerances of the delay line. An external network is required from pin 6 of the
TDA256O to provide d. c. negative feedback in the chroma channel via pins I and 2.
Burst gating and clamping pulse input
A two-level pulse is required at this pin to be used for burst gate and black level
clamping. The black level clamp is activated when the pulse level is greater than
7 V. The timing of this interval should be such that no appreciable encroachment
occurs into the sync pulse on picture line periods during normal operation of the
receiver. The burst gate, which switches the gain of the chroma amplifier to
maximum, requires that the input pulse at pin 7 should be sufficiently wide, at least
8 ps, at the actuating level of 2,3 V.

+12 V power supply
Correct operation occurs within the range 10 to 14 V. All signal and control levels
have a linear dependency on supply voltage but, in any given receiver design, this
range may be restricted due to considerations of tracking between the power supply
variations and picture contrast and chroma levels.
Flyback blanking input waveform
This pin is used for blanking the luminance amplifier. When the input pulse exceeds
the +2, 5 Vlevel, the output signal is blanked to a level of about 0 V. When the input
exceeds a +6 V level, a fixed level of about 1, 5 V is inserted in the output. This
level can be used for clamping purposes.
Luminance sigal output
An emitter follower provides a low impedance output signal of 3 V black-to-white
amplitude at nominal contrast setting having a black level in the range 1 to 3 V. An
external emitter load resistor is not required.
The luminance amplitude available for nominal contrast may be modified according
to the resistor value from pin 13 to the +12 V supply. At an input bias current
114 of 0,25 mA during black level the amplifier is compensated so that no black
level shift more than 10 mV occurs at contrast control. When the input current
deviates from the quoted value the black level shift amounts to 100 mV/rnA.
Brightness control
The black level at the luminance output (pin 10) is identical to the control voltage
required at this pin, A range of black level from l to 3 V may be obtained.
Black level clamp capacitor
Luminance gain setting resistor
The gain of the luminance amplifier may be adjusted by selection of the resistor
value from pin 13 to +12 V. Nominal luminance output amplitude is then 3 V
black-to-white at pin 10 when this resistor is 2, 7 l



TDA2541 IF AMPLIFIER WITH DEMODULATOR AND AFC
DESCRIPTION
The TDA2540 and 2541 are IF amplifier and A.M.
demodulator circuits for colour and black and white
television 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
play back).


.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


TDA2590 horizontal oscillator combination

GENERAL DESCRIPTION
— The TDA2590 is a monolithic integrated circuit designed
as a horizontal oscillator combination for TV receivers and monitors.

It is constructed using the Fairchild Planar* process.
LINE OSCILLATOR USING THE THRESHOLD SWITCHING PRINCIPLE
PHASE COMPARISON BETWEEN SYNC PULSE AND OSCILLATOR VOLTAGE (d>1)
PHASE COMPARISON BETWEEN LINE FLYBACK PULSE AND OSCILLATOR VOLTAGE
(<62) Y
SWITCH FOR CHANGING THE FILTER CHARACTERISTIC AND THE GATE CIRCUIT
{WHEN USED FOR VCR)
COINCIDENCE DETECTOR (¢3)
SYNC SEPARATOR
NOISE SEPARATOR
VERTICAL SYNC SEPARATOR AND OUTPUT STAGE
COLOR BURST KEYING AND LINE FLYBACK BLANKING PULSE GENERATOR
PHASE SHIFTER FOR THE OUTPUT PULSE
OUTPUT PULSE DURATION SWITCHING
OUTPUT STAGE FOR DIRECT DRIVE OF THYRISTOR DEFLECTION CIRCUITS
SYNC GATING PULSE GENERATOR
LOW SUPPLY VOLTAGE PROTECTION.













 

 DIGITAL CLOCK ON SCREEN DISPLAY MEYHOD:

The introduction of l.s.i. MOS integrated circuits has allowed semiconductor manufacturers to include many complex functions on one chip. General Instruments have produced several such chips for the TV industry, amongst the more interesting being the AY-5-8300 8320 series of channel and time display chips. These provide video outputs which superimpose a digital clock or the channel number on the television picture. It's interesting to see how fast semiconductor technology has advanced even in the 70's.

Circuit Description:
The display chip chosen for this post is the AY-5-8320. This provides a four digit clock display with decimal point and a channel number display from 1-16. Both displays appear on a background rectangle for easy viewing. The time and channel displays can be enabled independently. To the display chip we must add a digital clock. This is again an l.s.i. MOS chip, the G.I. AY-5-1203A. Like most digital clocks it uses the 50Hz mains as a clock input, with digital counters to produce the time display output. Pin connections for the two l.s.i. chips, and a typical TV display, are shown on Fig. 1. 

The circuit diagram of the digital clock and the character generator is shown on Fig. 2: ICI is the 1203 digital clock chip and IC2 the display chip. The digital clock produces a four -digit output. To transmit this in binary form would require sixteen lines. The clock chip economises on pin connections by sending each digit (four binary bits) in turn. This is called multiplexing. These four binary bits are available at pins 16 to 19 of the 1203. To identify the digits as they are sent, the 1203 provides four multiplex slot signals MX1-4 which appear at pins 3-6. When MX1 is at a 
binary 1 the minutes units binary bits are on pins 16 to 19, when MX2 is at a 1 the minutes tens binary bits are present and so on. A strobe output is provided at pin 20. This occurs in the centre of each multiplex slot, and is used by the display chip to gate the data from the clock. The display chip thus obtains and stores all four digits of the time display. The multiplexing frequency is determined by a capacitor (C2) from pin 23 to the positive supply. It is nominally set to 50kHz, although this is not critical. The AY5-8320 display chip IC2 requires (in addition to the time data) line and field sync pulses to position the display, and a 1.1MHz oscillator input. The 1.1MHz oscillator has to be inhibited by the line sync pulse and synchronised on each TV line to prevent ragged edges appearing on the characters. The oscillator consists of the quad CMOS nand IC3, with the frequency of oscillation determined by R3, RV1, C1. 
 
The sync pulses are produced by the sync extraction circuit shown in Fig. 3 (to be described later).
These pulses may be positive -going or negative -going depending on the TV set being used. The circuit requires positive -going line sync pulses at pins 8 and 9 of IC3, and negative -going field sync pulses at pin 7 of IC2. The inverters (IC4 a -d) and the wire links allow the correct polarity signal to be chosen. There is little data available as to what actually goes on inside the 8320 display chip, although it is probably along the lines of the score display article in the September 1975 Practical Wireless . The necessary delays will be generated by digital counters from the 1.1MHz clock. The display chip IC2 produces two outputs, a time output on pin 3 and a background output on pin 2. These are at a binary 1 in the asserted state. These outputs are buffered by IC5 and inverters IC4 e and f to produce the following signals for the video switching: (a) Gate Video. This is at a binary 1 when the normal TV picture is present on its own and at a 0 when the background and time display are added. (b) Gate Time. This is the video output for the time/channel digits and is at a 1 in the asserted state. (c) Background a (IC5 pin 11). This is the background output, inhibited during the time display. It's at a 1 during the background but at a 0 during the time/channel display. (d) Background b (IC4 pin 6). This is a 1 for the entire background and time display. Depending on the colours required for the number and background, the "gate hue" and "gate background" outputs can be taken from background a or b by selecting the corresponding wire links. The time display is produced by taking pin 22 of IC2 to a binary 1. Capacitor C5 keeps the display on for about six seconds after the 1 input is removed. Pin 22 can be triggered by a momentary contact on a push-button or, ultimate luxury, from an ultrasonic remote transmitter.

The time is set by connections A and B. Taking A to a 1 advances the minutes display at two per second; taking B to a 1 similarly advances the hours. The 50Hz clock arrives via C3 and is clipped and buffered by R7, R8, D2, D3. The clock chip IC1 produces at pin 7 a 50kHz burst for 0.5 seconds every second. This is smoothed by R4, D I, C4 and presented to the colon input (pin 20) on the display chip to give a flashing colon display. Some people find flashing colons annoying: if R4, D 1 and C4 are omitted and R6 is inserted the colon becomes steady. The colon output from the clock also drives Tr4 to give a front panel LED display. The colon stops flashing after a power failure, and starts again when either of the set time buttons is pressed. The front panel LED thus indicates that the clock is healthy. The channel data is presented in binary form at terminals W, X, Y, Z, W being the least significant bit. The display is offset by one bit, i.e. 0000 gives 1, 0100 gives 5 and so on. The channel display is enabled by taking terminal V to a binary 1.

Interfacing with the Television Receiver:
Fig. 3 shows the sync extraction circuits and a general purpose video mixing circuit. Before describing these it's probably best to outline the basic requirements of the television interface. The display system needs field and line sync signals from the television receiver. It's highly unlikely that these would be available at the correct levels, and depending on the set and the take off point chosen they can be of either polarity. If oscillograms are shown in the service manual, suitable signals should be easily found - in most if not all television sets. They will probably be found in either the sync separator, the flyback blanking circuits or around the scan output stages. If oscillograms are not available it will be necessary to do a bit of detective work around likely points in the circuit. It's preferable to use scan flyback pulses because of their amplitude and the low source impedance (this avoids loading the sync circuits). 
The sync extraction circuits shown in Fig. 3 will accept either positive- or negative -going signals. For negative - going inputs, Trl and Tr2 are forward biased by R14/R18: with positive -going inputs R13/R17 are used instead. The input resistors R12 and R16 form a potential divider with the selected resistor, and the transistors are turned on for positive inputs or off for negative inputs. The wire links shown in Fig. 2 allow the correct polarity signals to be chosen for the display circuit. The values for R12-14 and R16-18 depend on the amplitude of the incoming waveforms. Transistors Tr 1/Tr2 need about 0.1mA base current, so the values will be of the order of 100kS2. This should not load the TV circuit to which it's connected. With some waveforms which are close to or cross OV, capacitors C6 and C7 can be replaced with wire links. If C6 and C7 are used they should be of suitable voltage rating for the circuit to which they are connected. The connection to the video stages presents many options. The majority of colour TV sets today are cathode driven with RGB signals. The description of techniques for interfacing the time display with the set's video circuitry will be mainly directed at cathode drive therefore.

 A, typical simple RGB output stage is shown in Fig. 4. The RGB signal from the demodulator i.c. is fed first to a preamplifier or buffer (generally a one transistor stage) then to the high -voltage transistor which drives the appropriate c.r.t. cathode.





 A "brute force and ignorance" method of inserting the time and background display is to parallel three high - voltage transistors Tr 1 etc. with the RGB outputs along the lines shown in Fig. 5. The signals driving these could be
picked up from the "gate time", "gate background a and b" outputs (Fig. 2). The trimpots RV1 etc. set the current through the output transistors and hence the cathode potentials when the logic signals are at a binary 1. By selection of the right logic signals and suitable settings of the trimpots almost any colour combination for the time and its background could be chosen.

To prevent the display appearing superimposed on the video from unused cathodes, it will again be necessary to resort to brute force. Transistors Tr2 etc. pull down the bases of the buffer preamplifier transistor, turning the television RGB signals off. These transistors are driven from the "background b" signal which is present for the entire display on each line. A more subtle method is to use the 4016 CMOS analogue switch to intercept the video from the demodulator i.c. and substitute in its place the time display. The 4016 i.c. looks like a perfect switch in series with a 300E2 resistor. The switch is controlled by the logic gate input, the switch being closed for a binary 1 and open for a binary 0. The operating time is around 200nS, which is adequate for our application. Cathode drive RGB output stages fall into two categories: direct coupled from the demodulator to. the cathode with clamping earlier in the circuit, or a.c. coupled with clamping at the c.r.t. cathodes. Direct coupled amplifiers are the easiest ones to modify, so these will be dealt with first.

 All that's usually required here is to insert the 4016 switch in the base circuit of the output transistor. Fig. 6 shows a suitably modified red drive circuit. Switch SW1 controls the video and SW2 the voltage set by RV1. Switch SW1 is closed by the "gate video" signal from Fig. 2, and SW2 from the selected logic output (gate time, background or hue). The other two amplifiers are dealt with in a similar manner. One small modification is required to the output from the demodulator i.c. This doesn't like having no load, tending to wander off and do its own thing when the video switches are open. To prevent this, a 10k52 resistor should be added from pins 1, 2 and 4 to OV as shown. Next we must deal with a.c. coupled circuits.

A typical example is the tv chassis here described.

 The RGB output circuit (red one) used in this chassis is shown in Fig. 7. The simplest way to deal with this is to insert the 4016 switch at the point shown. Because the video is unclamped at this point, the time display levels will vary according to the picture content. For the best results it's necessary to clamp the video before substituting the time display. This is done by the transistor clamp shown in Fig. 7. The video is a.c. coupled and clamped by Tr 1. The clamp voltage of 4.7V is chosen to bias the 4016 switches in the centre of their range. The clamped video is then switched, along with the d.c. levels from the trimpot RV I, to insert the time display. The modified video is then a.c. coupled back to 3RV8 on the TV chassis. The 30052 resistance of the 4016 is effectively connected in series with 3RV8 etc. These may require slight adjustment therefore. Alternatively the dearer 4066 chip may be used. This is identical to the 4016, but has a resistance of 6052. With the general description over we can turn to the circuit in Fig. 3. IC6 and IC7 are two quad CMOS switches. IC6 gates the video from the three demodulator outputs. IC7 gates the levels on RV2 RV4 to give the three outputs on pins K, L, M. The fourth, Y, is used in older colour -difference sets and will be described later. The gating of the levels on RV2 - RV4 is done by the gate logic signals from Fig. 2. Also shown in Fig. 3 is the power supply. This is a fairly conventional i.c. regulator, made adjustable by the inclusion of Tr3 in the common return line. The operating voltage range for IC I is 12-18V, for IC2 it's 16-19V, and for the B picked up from the "gate time", "gate background a and b" outputs (Fig. 2). The trimpots RV1 etc. set the current through the output transistors and hence the cathode potentials when the logic signals are at a binary 1. By selection of the right logic signals and suitable settings of the trimpots almost any colour combination for the time series CMOS it's less than 18V. The supply chosen is 16- 17V therefore. A wire link is included so that the power supply can be adjusted before it's connected to the rest of the circuit.



SABA ULTRACOLOR CHASSIS CM110 Controlled power supply for a television receiver equipped with remote control:BLAUPUNKT SWITCH MODE POWER SUPPLY.Blaupunkt-Werke GmbH (Hildesheim, DT)

A single isolation transformer supplies both the remote control receiver and the television receiver. A pulse generator such as a blocking oscillator which energizes the primary winding of the isolation transformer has its pulse width controlled in response to the loading of the circuit of the secondary winding of the isolation transformer, as measured by the voltage across a resistor in the circuit of a primary winding. This measuring resistor is interposed between the emitter of the switching transistor of the blocking oscillator and the receiver chassis. A transistor switching circuit for cutting off the low voltage supply to the scanning circuit oscillators of the television receiver is responsive to the output of the remote control receiver, to a signal from an operating control of the television receiver, and to an indication of overcurrent in the picture tube, independently.

1. A power supply circuit for a television receiver equipped for remote control comprising, in combination:
an on-off switch for connecting and disconnecting the television receiver and its power supply circuit respectively to and from the electricity supply mains;
pulse generating means arranged for energization through said on-off switch;
an isolation transformer having its primary winding supplied with the output of said pulse generating means;
a power conversion circuit connected to the secondary winding of said isolation transformer for energization thereby, for supplying an operating voltage for the scanning circuits of the television receiver and for supplying a plurality of other voltages to said receiver, at least one of which other voltages is also supplied to said scanning circuits;

a remote control signal receiver for remote control of said television receiver and controlled switching means responsive to said remote control receiver for switching said television receiver between a stand-by condition and an operating condition, both said remote control receiver and said controlled switching means being connected to a secondary winding of said isolation transformer for energization thereby, said controlled switching means having a switching path for connecting and disconnecting said scanning circuits of said television receiver respectively to and from a source of said operating voltage in said power conversion circuit and
means for reducing energy transfer through said pulse generating means to said isolation transformer when said television receiver is in the stand-by condition.
2. A power supply circuit as defined in claim 1, in which said pulse generating means includes rectifying means energized through said on-off switch for supplying direct current for energization of said pulse generating means. 3. A power supply circuit as defined in claim 2, in which said energy transfer reducing means includes means for varying the width (duration) of pulses generated by said pulse generating means in response to the extent of loading of the secondary circuit of said isolating transformer as measured in the primary circuit of said transformer. 4. A power supply circuit as defined in claim 2, in which said pulse generating means includes a blocking oscillator and said energy transfer reducing means includes means for reducing the width (duration) of the pulses generated by said blocking oscillator. 5. A power supply circuit as defined in claim 4, in which said blocking oscillator includes a switching transistor (5) and a load measuring resistor (7) interposed in a connection between the emitter of said switching transistor and the receiver chassis, and in which said pulse width reducing means is responsive to the voltage drop across said load measuring resistor. 6. A power supply circuit as defined in claim 5, in which said pulse width reducing means includes a controllable resistance (10) in the circuit of said blocking oscillator controlled in response to the voltage drop across said load measuring resistor. 7. A power supply circuit as defined in claim 1, in which said operating voltage connected and disconnected to said scanning circuits by said controlled switching means is the low voltage supply voltage (U 3') of the line scan and picture scan oscillators of the television receiver and in which said controlled switching means is controlled so as to switch off said low voltage supply voltage to put the television receiver in the stand-by condition. 8. A power supply circuit as defined in claim 7, in which said controlled switching means includes a first switching transistor (15) at the collector of which there is applied a direct current supply voltage (U 3) energized through said isolating transformer and a second switching transistor (24) for controllably short-circuiting the base bias of said first switching transistor, whereby a stabilized low voltage (U 3') exists at the emitter of said first switching transistor (15) when a positive signal is supplied from an operating control of the television receiver or from said remote control receiver to the base of said second switching transistor (24). 9. A power supply circuit as defined in claim 7, in which said controlled switching means is responsive independently to an overcurrent condition in the picture tube for switching off said low voltage supply voltage (U 3') in response to said overcurrent condition.

Description:

The present invention relates to a power supply unit including a blocking oscillator for utilization with a television receiver provided with ultrasonic remote control, and more particularly to a television receiver the operating conditions of which are normal operation, a stand-by operation, and the turned-off condition, and a power supply unit therefor that includes an isolating transformer.
In recent times television receivers have frequently been provided with ultrasonic remote control devices for the purpose of offering easier control. As more and more television receivers are utilized in combination with additional equipment, it becomes increasingly necessary to connect the receivers only indirectly to the electric power mains (house wiring). In a known advantageous solution of this problem, a power supply unit includes an isolating transformer which is wired up with a blocking oscillator in the primary circuit. The blocking oscillator is supplied with a d-c voltage which is obtained by rectification of the supply voltage. Compared to the isolating transformers which are directly mains-operated, these so-called switch-mode power supply units have the advantage that they can be made in considerably smaller size, as they are operated at a significantly higher frequency, and the further advantage that they require less expensive means for rectification.
It is necessary to supply television receivers equipped with ultrasonic remote control with the possibility for a stand-by operation in which only the ultransonic receiver is supplied with power and, in some cases, also the heating current for the picture tube. Usually a separate power supply unit is provided for the ultrasonic receiver and the heating of the picture tube, a unit that includes an isolating transformer of its own, the primary winding of which is directly mains-fed. Upon transition from normal operation to stand-by operation, the power supply unit of the blocking osciallator is switched off, so that the television receiver receives only the relatively small quantity of energy required for the ultrasonic receiver and, in some cases, also for the heating of the picture tube.
Because of the required second isolating transformer, this known circuit has the disadvantages that it requires both greater space and greater expenditure.
It is the object of the present invention to develop a simplified power supply unit which does not have the above-mentioned disadvantages.
SUMMARY OF THE INVENTION
Briefly, the television receiver and the ultrasonic receiver are connected to the same isolating transformer; means for the switching from normal operation to stand-by operation and vice versa are placed in the secondary circuit of the isolating transformer, and means are arranged in the primary circuits of the isolating transformer for reducing the amount of energy made available for stand-by operation purposes.
The main advantages of the present invention are that no separate isolating transformer is required for supplying the current during the stand-by operation, and that, during the stand-by operation, it is nevertheless only the power required for this operation which is consumed.
An advantageous embodiment of the present invention obtains reduction of the energy quantum transmitted through the power supply during stand-by by reduction of the pulse width of the pulses generated by the blocking oscillator.
Another advantageous embodiment of the present invention utilizes measurement in the primary circuit of the isolating transformer of variation in load occurring in the secondary circuit as a control variable for determining the pulse width.
A further advantageous embodiment of the present invention obtains the control variable for the pulse width across a measuring resistor interposed in the connection of the emitter of the switching transistor of the blocking oscillator to the chassis.
Still another advantageous embodiment of the present invention provides that the voltage drop across the measuring resistor controls a controllable resistor.
The advantageous embodiments described above offer highly simple and advantageous possibilities for measuring the variation in load upon switching between normal and stand-by operation, as well as for the consequent control of the energy transmitted via the isolating transformer.
The possibility of a simple and inexpensive switching between normal and stand-by operation is achieved by effecting the switching between normal and stand-by operation by means of switching on or switching off, respectively, the low voltage supply of the line scan oscillator, and, especially, by a first switching transistor which short-circuits the base bias of a second switching transistor at the collector of which a direct current supply voltage is present and at the emitter of which a stabilized low voltage exists, when a positive signal is supplied from the operating control of the television receiver or from the remote control receiver to the base of the first switching transistor.
The circuit arrangements just mentioned offer the advantage that they may simultaneously be utilized as a protective circuit. This is achieved by a switching-off device for the low voltage which can also be triggered at any time by a signal built up by overcurrent in the picture tube.

BRIEF DESCRIPTION OF THE DRAWINGS
The invention is further described by way of illustrative example by reference to the annexed drawings in which:
FIG. 1 is a circuit diagram, partly in block form, of an embodiment of the invention;
FIG. 2 is a circuit diagram of one form of means for interrupting the power to the picture circuits in the stand-by condition in connection with the circuit of FIG. 1, and
FIG. 3 is a circuit diagram of one way of controlling the pulse width of the blocking oscillator 4 in response to the switching circuit 8 in the circuit of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An on-off power switch 2 of the television receiver is connected to the supply terminals 1, providing a primary operating control for the receiver. Consquently, the supply voltage is also present at the output of the operating control 2 when the television receiver is turned on thereby, and arrives at a rectifying stage 3 comprising means for rectifying and smoothing the supply current as well as for suppressing interference. A d-c voltage, feeding a blocking oscillator stage 4, is present at the output of the recifying stage 3. The main part of the blocking oscillator 4, symbolically represented in FIG. 1 by a fragmentary circuit diagram, is a switching transistor 5, in the load circuit of which the primary winding of an isolating tranformer 6 is placed. A measuring resistor 7 is connected between the emitter of the switching transistor 5 and the chassis, across which measuring resistor a voltage is taken and applied to a load-dependent control circuit 8. The voltage taken at the measuring resistor 7 is fed via a resistor 9 to the base of a transistor 10 which serves as a controllable load for the blocking oscillator 4. A resistor 11 and a capacitor 12, each of which is connected to chassis with its other terminal, are also connected to the base of the transistor 10. The emitter of transistor 10 is connected to chassis, while the collector of the transistor 10 is connected back to the blocking oscillator stage 4.
In the secondary circuit of the isolating transformer 6, a d-c voltage supply stage or power conversion circuit 13 is placed, substantially consisting of a rectifying circuit 14, which, in the example shown, is provided with six outputs at which the voltages U 1 to U 5 can be taken off with respect to the sixth output connected to the chassis. At the terminal U 3, there is, in addition, a branch feeding both the collector-to-emitter path of the transistor 15 and also, through a resistor 16, the collector-to-emitter path of the transistor 15a. The emitter of the transistor 15a is directly connected to the base of transistor 15. The emitter of the transistor 15 is connected to chassis via a series connection of a resistor 17, a potentiometer 18, and a further resistor 19. The tap of the potentiometer 18 is connected to the base of a further transistor 20. The transistor 20 is connected to chassis by means of its emitter via a Zener diode 21, the collector of the transistor 20 controlling the base of the transistor 15a. The emitter of the transistor 20 is connected to the emitter of the transistor 15 via a resistor 22. A terminal for tapping off the voltage U 3' is connected to the emitter of the transistor 15.
The base of the transistor 15a is connected to a switching stage 23 responsive to a remote control ultrasonic receiver by a conductor leading to the collector of a switching transistor 24 which is connected to chassis via its emitter. The base of the switching transistor 24 is connected to an input terminal 28 leading into the television receiver via two resistors 25, 26 and a capacitor 27 connected in series, that input terminal 28 passing on switching signals from the receiver to the switching transistor 24, as will be explained in more detail below.
The cathode of a diode 29, which is connected to chassis via its anode, is connected to the junction point of the resistor 26 and the capacitor 27. The junction point of the two resistors 25, 26 is connected to chassis via a capacitor 30. The base of the switching transistor 24 is connected to chassis via a resistor 31. Furthermore, that base electrode is also connected to a terminal 32 to which an electrical switching signal is applied which is either built up in response to an ultrasonic signal received by the remote control receiver 32' or is supplied from an operating control of the television receiver. At the terminal 32, the switching transistor 24 receives the signal containing the information whether the television receiver is to work in the normal operating condition, i.e. to receive and process the sound and video signals, or in the stand-by condition in which it is substantially only the ultrasonic receiver that is supplied with current.
When a positive signal arrives at the base of the switching transistor 24, the latter becomes conductive, and causes chassis potential to be present at the base of transistor 15a. The transistor 15 is thereby blocked, and there is no longer any voltage at the terminal U 3'. Since the voltage U 3' serves as an operating voltage for the line and picture scan oscillator, the deflecting stages of the receiver cannot work and no high voltage and other related supply voltages are generated at the line circuit transformer. In consequence, by means illustrated diagrammatically in FIG. 2, the electric circuits connected to the terminals U 1 to U 3 are interrupted. The voltages U 4 and U 5 serve for supplying the ultrasonic receiver, i.e. they are required for the stand-by operation.
In case no counteracting means should be provided for, the variation in load would cause a voltage rise in the secondary circuit of the isolating transformer 6, which effect is, of course, not desired. Therefore, a measuring resistor is connected in the primary circuit in the emitter line of the switching transistor 5 of the blocking oscillator 6, the variation in load in the secondary circuit appearing at the measuring resistor 7 as a current variation. The current change thus produced, causes a variation in the base bias of the transistor 10, the capacitor 12 having an integrating effect to avoid undesired effects due to interference pulses and abrupt load fluctuations.
The change of the working point of the transistor 10 causes a change in the pulse width in the blocking oscillator stage 4, as more fully shown in FIG. 3, so that the energy quantum transmitted via the isolating transformer 6 is such that the required voltages are present in the secondary circuit. It should also be mentioned that the load-dependent switch 8 and the circuit of FIG. 3 are represented only by way of illustration and that many circuit arrangements may be devised by straight-forward application of known principles for controlling the pulse width.

The circuit connected between the terminal 28 and the base of the switching transistor 24 serves as a part of a protective circuit for the picture tube. Any overcurrent is measured at the low-end resistor 31 of the high-voltage cascade in conventional techinque. The voltage thus produced is fed to the base of the switching transistor 24, and causes the television receiver to be switched over to stand-by operation, so that no damage can be done to the picture tube. Thus, the device performing the switching between normal operation and stand-by operation is advantageously and simultaneously utilized as a protective circuit. The circuit 23, as shown, provides for stabilizing the potential at the base of transistor 24 and for integrating such possibly occurring overload peaks as are not intended to triggering the protective circuit.
Using the circuit diagram according to FIG. 3 it is possible in a simple manner to control the pulse width of the blocking oscillator 4 in response to the switching circuit 8.
According to the circuit diagram of FIG. 2 the terminal U1 is connected to a line scan oscillator circuit 40, the terminal U2 to a picture scan oscillator circuit 41 and the terminal U3 to a circuit 42 for a sound output stage. The circuits 40, 41, 42 get their operating voltage from the terminal U3'. If the operating voltage U3' is zero, the circuits 40, 41, 42 are interrupted. In this case the voltages at the terminals U1, U2, U3 remain.

The described circuit of this invention for controlling the voltage in the secondary circuit of the isolating transformer 6 offers the advantage that it is exclusively arranged in the primary circuit, and, therefore, permits an uncomplicated design which is easy to realize. To control the pulse width by measuring the load fluctuations at the low-end resistor of the switching transistor 5, represents a very useful means for control since, thereby the transmitted energy can effectively and easily be controlled.
The blocking oscillator stage 4 shown in detail in FIG. 3 incorporates an externally triggered blocking oscillator arranged to be triggered through an oscillator operating preferably at the line scanning frequency, which is to say its wave form is not particularly critical and it should be provided with means to keep it in step with the line scanning frequency, as is known to be desirable. The transistors 51 and 52 of the triggered output stage of the blocking oscillator circuit could be regarded as constituting a differential amplifier the inputs of which are defined by the base connections of the respective transistors 51 and 52. The input voltage applied to the base connection of transistor 52 is the Zener voltage of the Zener diode 53, thus a constant reference voltage. The operating voltage for the transistors 51 and 52 and for the Zener diode 53 is obtained from the supply voltage U_B, which is to say from the rectifier 3. The diode 67 protects the transistor 52, for example at the time of the apparatus being switched on, against damage from an excessively high emitter-base blocking voltage. The capacitor 65 prevents undesired oscillation of the circuit of transistors 51 and 52, which could give rise to undesired disturbances.
At the base of the transistor 51, there is present as input voltage for the circuit a composite voltage that is the sum of three voltages. These are, first, the line scan frequency trigger voltage coupled through the capacitor 63; second, a bias voltage dependent upon the loading of the blocking oscillator stage resulting from the load on the secondary of the transformer 6, but detected by the voltage across the resistor 7 and actually controlled by the load-sensitive control circuit 8, and, third, a regulating voltage applied at the terminal 71 of the resistor 70, which regulating voltage is proportional to the voltage of the secondary winding of the transformer 6 and can accordingly be provided by one or another of the output circuits of the rectifier 14 of FIG. 1 or by a separate winding of the transformer 6 and a separate rectifier element connected in circuit therewith. This regulating voltage and the control voltage provided by the control circuit 8 are applied to the resistor 61 which completes the circuit for both of these bias voltages and their combined effect constitutes the bias voltage for the transistor 51 which determines its working point.
The circuit of the transistors 51 and 52 operates as an overdriven differential amplifier. When the trigger voltage exceeds the threshold determined by the base voltage of the transistor 51, the circuit produces an approximately rectangular output voltage pulse of constant amplitude. Since the trigger voltage is recurrent, the result is a periodic succession of rectangular output voltage pulses, but the duration or pulse width of these pulses depends upon the loading and the output voltage of the stage. The output voltage of the circuit constituted by the transistors 51 and 52 comes from the emitter connection of the transistor 52 and is furnished to the switching transistor 5, preferably through a driver stage 54, such as a transformer or another transistor stage for better matching of the circuit impedances. Of course, the collector circuit of the transistor 5 includes the primary winding of the transformer 6 of FIG. 1.

The described power supply unit thus represents a well functioning component subject to but a small number of potential sources of error, due to the simple design, and permits considerable reduction of costs in comparison with circuits and equipment heretofore known.