3 x transistor TV power supply. LCD TV power supply. This module is functionally divided into several nodes

How to assemble a simple power supply and a powerful voltage source yourself.
Sometimes you have to connect various electronic devices, including homemade ones, to a 12 volt DC source. The power supply is easy to assemble yourself within half a weekend. Therefore, there is no need to purchase a ready-made unit, when it is more interesting to independently make the necessary thing for your laboratory.

Anyone who wants can make a 12-volt unit on their own, without much difficulty.
Some people need a source to power an amplifier, while others need a source to power a small TV or radio...
Step 1: What parts are needed to assemble the power supply...
To assemble the block, prepare in advance the electronic components, parts and accessories from which the block itself will be assembled....
- Circuit board.
-Four 1N4001 diodes, or similar. Diode bridge.
- Voltage stabilizer LM7812.
-Low-power step-down transformer for 220 V, the secondary winding should have 14V - 35V alternating voltage, with a load current from 100 mA to 1A, depending on how much power is needed at the output.
-Electrolytic capacitor with a capacity of 1000 µF - 4700 µF.
-Capacitor with a capacity of 1uF.
-Two 100nF capacitors.
-Cuttings of installation wire.
-Radiator, if necessary.
If you need to get maximum power from the power source, you need to prepare an appropriate transformer, diodes and a heatsink for the chip.
Step 2: Tools....
To make a block, you need the following installation tools:
-Soldering iron or soldering station
-Pliers
-Installation tweezers
- Wire strippers
-Device for solder suction.
-Screwdriver.
And other tools that may be useful.
Step 3: Diagram and others...

To obtain 5 volt stabilized power, you can replace the LM7812 stabilizer with an LM7805.
To increase the load capacity to more than 0.5 amperes, you will need a heatsink for the microcircuit, otherwise it will fail due to overheating.
However, if you need to get several hundred milliamps (less than 500 mA) from the source, then you can do without a radiator, the heating will be negligible.
In addition, an LED has been added to the circuit to visually verify that the power supply is working, but you can do without it.

Power supply circuit 12V 30A.
When using one 7812 stabilizer as a voltage regulator and several powerful transistors, this power supply is capable of providing an output load current of up to 30 amperes.
Perhaps the most expensive part of this circuit is the power step-down transformer. The voltage of the secondary winding of the transformer must be several volts higher than the stabilized voltage of 12V to ensure the operation of the microcircuit. It must be borne in mind that you should not strive for a larger difference between the input and output voltage values, since at such a current the heat sink of the output transistors increases significantly in size.
In the transformer circuit, the diodes used must be designed for a high maximum forward current, approximately 100A. The maximum current flowing through the 7812 chip in the circuit will not be more than 1A.
Six composite Darlington transistors of the TIP2955 type connected in parallel provide a load current of 30A (each transistor is designed for a current of 5A), such a large current requires an appropriate size of the radiator, each transistor passes through one sixth of the load current.
A small fan can be used to cool the radiator.
Checking the power supply
When you turn it on for the first time, it is not recommended to connect a load. We check the functionality of the circuit: connect a voltmeter to the output terminals and measure the voltage, it should be 12 volts, or the value is very close to it. Next, we connect a 100 Ohm load resistor with a dissipation power of 3 W, or a similar load - such as an incandescent lamp from a car. In this case, the voltmeter reading should not change. If there is no 12 volt voltage at the output, turn off the power and check the correct installation and serviceability of the elements.
Before installation, check the serviceability of the power transistors, since if the transistor is broken, the voltage from the rectifier goes directly to the output of the circuit. To avoid this, check the power transistors for short circuits; to do this, use a multimeter to separately measure the resistance between the collector and emitter of the transistors. This check must be carried out before installing them in the circuit.

Power supply 3 - 24V

The power supply circuit produces an adjustable voltage in the range from 3 to 25 volts, with a maximum load current of up to 2A; if you reduce the current-limiting resistor to 0.3 ohms, the current can be increased to 3 amperes or more.
Transistors 2N3055 and 2N3053 are installed on the corresponding radiators; the power of the limiting resistor must be at least 3 W. Voltage regulation is controlled by an op-amp LM1558 or 1458. When using an op-amp 1458, it is necessary to replace the stabilizer elements that supply voltage from pin 8 to op-amp 3 from a divider on resistors rated 5.1 K.
The maximum DC voltage for powering op-amps 1458 and 1558 is 36 V and 44 V, respectively. The power transformer must produce a voltage at least 4 volts higher than the stabilized output voltage. The power transformer in the circuit has an output voltage of 25.2 volts AC with a tap in the middle. When switching windings, the output voltage decreases to 15 volts.

1.5 V power supply circuit

The power supply circuit to obtain a voltage of 1.5 volts uses a step-down transformer, a bridge rectifier with a smoothing filter and an LM317 chip.

Diagram of an adjustable power supply from 1.5 to 12.5 V

Power supply circuit with output voltage regulation to obtain voltage from 1.5 volts to 12.5 volts; the LM317 microcircuit is used as a regulating element. It must be installed on the radiator, on an insulating gasket to prevent a short circuit to the housing.

Power supply circuit with fixed output voltage

Power supply circuit with a fixed output voltage of 5 volts or 12 volts. The LM 7805, LM7812 microcircuit is used as an active element; it is installed on a radiator to cool the heating of the case. The choice of transformer is shown on the left on the plate. By analogy, you can make a power supply for other output voltages.

20 Watt power supply circuit with protection

The circuit is intended for a small homemade transceiver, author DL6GL. When developing the unit, the goal was to have an efficiency of at least 50%, a nominal supply voltage of 13.8V, maximum 15V, for a load current of 2.7A.
According to what scheme: switching power supply or linear?
Switching power supplies are small-sized and have good efficiency, but it is unknown how they will behave in a critical situation, surges in the output voltage...
Despite the shortcomings, a linear control scheme was chosen: a fairly large transformer, not high efficiency, cooling required, etc.
Parts from a homemade power supply from the 1980s were used: a radiator with two 2N3055. The only thing missing was a µA723/LM723 voltage regulator and a few small parts.
The voltage regulator is assembled on a µA723/LM723 chip as standard. Output transistors T2, T3 type 2N3055 are installed on radiators for cooling. Using potentiometer R1, the output voltage is set within 12-15V. Using variable resistor R2, the maximum voltage drop across resistor R7 is set, which is 0.7V (between pins 2 and 3 of the microcircuit).
A toroidal transformer is used for the power supply (can be any at your discretion).
On the MC3423 chip, a circuit is assembled that is triggered when the voltage (surge) at the output of the power supply is exceeded, by adjusting R3 the voltage threshold is set on leg 2 from the divider R3/R8/R9 (2.6V reference voltage), the voltage that opens the thyristor BT145 is supplied from output 8, causing a short circuit leading to tripping of fuse 6.3a.

To prepare the power supply for operation (the 6.3A fuse is not yet involved), set the output voltage to, for example, 12.0V. Load the unit with a load; for this you can connect a 12V/20W halogen lamp. Set R2 so that the voltage drop is 0.7V (the current should be within 3.8A 0.7=0.185Ωx3.8).
We configure the operation of the overvoltage protection; to do this, we smoothly set the output voltage to 16V and adjust R3 to trigger the protection. Next, we set the output voltage to normal and install the fuse (before that we installed a jumper).
The described power supply can be reconstructed for more powerful loads; to do this, install a more powerful transformer, additional transistors, wiring elements, and a rectifier at your discretion.

Homemade 3.3v power supply

If you need a powerful power supply of 3.3 volts, then it can be made by converting an old power supply from a PC or using the above circuits. For example, replace a 47 ohm resistor of a higher value in the 1.5 V power supply circuit, or install a potentiometer for convenience, adjusting it to the desired voltage.

Transformer power supply on KT808

Many radio amateurs still have old Soviet radio components that are lying around idle, but which can be successfully used and they will serve you faithfully for a long time, one of the well-known UA1ZH circuits that is floating around the Internet. Many spears and arrows have been broken on forums when discussing what is better, a field-effect transistor or a regular silicon or germanium one, what temperature of crystal heating will they withstand and which one is more reliable?
Each side has its own arguments, but you can get the parts and make another simple and reliable power supply. The circuit is very simple, protected from overcurrent, and when three KT808 are connected in parallel, it can produce a current of 20A; the author used such a unit with 7 parallel transistors and delivered 50A to the load, while the filter capacitor capacity was 120,000 uF, the voltage of the secondary winding was 19V. It must be taken into account that the relay contacts must switch such a large current.

If installed correctly, the output voltage drop does not exceed 0.1 volt

Power supply for 1000V, 2000V, 3000V

If we need to have a high voltage DC source to power the transmitter output stage lamp, what should we use for this? On the Internet there are many different power supply circuits for 600V, 1000V, 2000V, 3000V.
First: for high voltage, circuits with transformers for both one phase and three phases are used (if there is a three-phase voltage source in the house).
Second: to reduce size and weight, they use a transformerless power supply circuit, directly a 220-volt network with voltage multiplication. The biggest drawback of this circuit is that there is no galvanic isolation between the network and the load, as the output is connected to a given voltage source, observing phase and zero.

The circuit has a step-up anode transformer T1 (for the required power, for example 2500 VA, 2400V, current 0.8 A) and a step-down filament transformer T2 - TN-46, TN-36, etc. To eliminate current surges during switching on and protection diodes when charging capacitors, switching is used through quenching resistors R21 and R22.
The diodes in the high-voltage circuit are shunted by resistors in order to uniformly distribute Urev. Calculation of the nominal value using the formula R(Ohm) = PIVx500. C1-C20 to eliminate white noise and reduce surge voltages. You can also use bridges like KBU-810 as diodes by connecting them according to the specified circuit and, accordingly, taking the required amount, not forgetting about shunting.
R23-R26 for discharging capacitors after a power outage. To equalize the voltage on series-connected capacitors, equalizing resistors are placed in parallel, which are calculated from the ratio for every 1 volt there are 100 ohms, but at high voltage the resistors are quite powerful and here you have to maneuver, taking into account that the open-circuit voltage is 1 more, 41.

Secrets of the TV master

B. KISELEVICH, Khatanga village, Krasnoyarsk Territory
Radio, 1998, No. 4

The so-called “three-transistor” power supply is a fairly common switching power supply that was used in many models of CRT TVs - PHILIPS - 2021, AKAI - ST-1407, AKAI - 2107, SHERION, CROWN - STA/ 5176, ELEKTA - CTR-1498EMK, RECOR and many more.

Power supply circuit

As an example, consider such a source used in the CROWN TV - CTV5176.
The 220 V mains voltage is supplied through the power filter to the rectifier BR601, C601 - C604 and to the demagnetization loop L2001. To the collector of the key transistor Q604, the rectified voltage passes through winding 1-5 of the pulse transformer T601.

A blocking generator is made on transistor Q604 - the positive feedback voltage is removed from winding 7 - 8 of the transformer. The duration of the pulses generated by the blocking generator, i.e., the time the transistor Q604 is in a saturated state, is determined by the operation of the pulse width modulator (PWM).

A capacitor C607 is connected to the base of the transistor Q604, which, during the closed state of the transistor, is charged by a voltage pulse of winding 7 - 8 of the transformer through the diode D604. When transistors Q602, Q603 open, the PWM capacitor C607 is connected to the emitter junction of the saturated transistor Q604, and the discharge current of the capacitor, flowing through the transistors and resistor R616, quickly closes the transistor Q604. The bias voltage is applied to the base of transistor Q604 through resistors R603, R604. Circuit C610R617 limits pulse surges on the collector of transistor Q604, thereby protecting it from breakdown.

To power the DC amplifier on transistor Q601, the alternating voltage from winding 9 - 10 is rectified by diode D603 and charges capacitor C606. The voltage at the emitter of transistor Q601 is stabilized by a parametric stabilizer on elements D601, R609, and the voltage to the base of the transistor is removed from the measuring resistive divider R606VR601R6 07. The latter depends on the voltage on winding 9 - 10 of the transformer, i.e., the output voltage levels of the power supply + 110 and +12 V. The voltage on resistor R608 - the collector load of transistor Q601 serves as an error voltage and controls the opening moment of PWM on transistors Q602, Q603. Trimmer resistor VR601 sets the output voltage to + 110 V.

A sawtooth voltage is removed from resistor R605 through circuit C605R611 to the base of transistor O602 of the PWM driver. The error voltage comes to it from the collector of transistor Q601. Depending on the last one, the PWM opens earlier or later, counting from the moment the transistor Q604 opens. Transistors Q602, Q603 are an analogue of a thyristor. The principle of its operation is similar to the operation of the thyristor in the MPZ-3 pulse power module.

When the network voltage increases or the load decreases, the voltage on winding 9 - 10 of transformer T601 increases. As a result, transistors Q602, Q603 open earlier, closing the output transistor Q604 at an earlier time. This reduces the energy stored in transformer T601, which compensates for the increase in network voltage.

When the network voltage decreases, the voltage on winding 9 - 10 of transformer T601 will be correspondingly lower. At the collector of transistor Q601, the error voltage decreases. The PWM opens at a later time, and the amount of energy transferred to the secondary circuit increases, compensating for the decrease in mains voltage.

The secondary rectifiers of the unit are made according to a half-wave circuit. Winding 4 - 2 transformers and elements D606, C612, L601 form a +12 V voltage source used to operate the remote control system and other low-current circuits. Winding 4 - 3 and elements D607, L602 are included in the +110 V voltage source that powers the horizontal scanning output stage.

Transistors Q608, Q606, Q605 are used to assemble a unit for turning on and off the power supply for the horizontal scanning output stage. Thus, the TV is turned on or off by the remote control system, i.e. it is switched to operating or standby mode. In standby mode, transistor Q606 is closed and the +110 V voltage is not supplied to the horizontal scan output stage. Some TV models use relays for this purpose.

For repairs, the unit board is removed from the TV case and placed so that there is easy access to the elements. A resistor with a resistance of 220 kOhm and a dissipation power of 0.5 W is connected in parallel to capacitor C604. The capacitor will discharge through it after the TV is turned off. Solder one of the terminals of each of the elements L601, L602, D608, C617. In this case, the TV's load circuits will be completely disconnected from the power supply. An incandescent lamp of 220 V and 25 W is connected in parallel to the capacitor C615, which will serve as the equivalent load of the power supply.

After the repair, before connecting the power supply to the TV circuits, you must check the horizontal output transistor and the secondary circuits of the horizontal transformer. Voltage is often taken from the secondary windings of the latter, rectified and smoothed to power the TV components. One of the reasons for the failure of the power supply may be precisely these circuits.

When selecting transistors to replace failed ones, you should be guided by their characteristics listed in table. 1.

Transistors 2SC1815Y can be replaced with KT3102B, 2SB774T with KT3107B, and 2SD820, BU11F with KT872A. The latter is mounted on a heat sink with an insulating gasket. Diodes can be replaced with KD209B, KD226A, KD226B.

The most common malfunction this module is “going into disarray” due to a decrease in capacity (or increase in ESR) of electrolytic capacitors. Moreover, the reason for this trouble is not even the quality of the parts used: the main problem is that modern switching power supplies operate at high frequencies (15 kHz or even higher...), and conventional electrolytes are simply not designed for such high frequencies and in During operation they begin to heat up.
If the filter capacitor (according to the diagram this is C606) more or less copes with its duties, then C607 works in a very difficult mode (it has to pass high-frequency pulses through itself).
Therefore, when repairing this SMPS, it is imperative to pay attention first of all to these capacitors, and repair the unit with the horizontal scan turned off, using an incandescent lamp with a power of 60...100 W as a load.

Note: most of the material is from Radio magazine, 1998, No. 4

Hi all!

In this article we will look at LCD TV power supply Samsung BN44-00192A , which is used in devices with screen diagonals of 26 and 32 inches. We will also look at some typical malfunctions of this module.

All components of this power supply located on one board. The appearance of the board is shown in the figure:

Power module diagram BN44-00192A can be found on this site.

This module is functionally divided into several nodes:

— Power Factor Correction (PFC) or power factor corrector (PFC);

— “standby” power supply;

— power supply “working”.

Let's look at each node separately.

Power factor corrector

This unit eliminates the harmonic components of the current in the input circuit, which are reproduced by the rectifier diodes together with the electrolytic filter capacitor of the mains rectifier of the switching power supply (SMPS). These harmonic components negatively affect the power grid, which is why manufacturers of household appliances are required to equip their products with PFC devices. Depending on the power, these devices are active and passive. In the BN44-00192A power supply we are considering, the PFC device is active.

Here PFC is turned on by switching voltage M_Vcc at pin 8 of the ICP801S controller simultaneously with the “working” power source. When the standby mode is turned on, the active PFC does not work, since the +311V voltage from the diode bridge through the DP801 diode is supplied to the filter capacitor. To filter harmonics at low loads, the installed input filters are sufficient. Essentially, these filters are passive PFCs.

Standby power supply

The standby power supply is a flyback converter circuit, which is controlled by an ICB801S PWM controller. The converter operating at a fixed frequency of 55...67 kHz generates a stabilized voltage of 5.2V at the output and has a load current of up to 0.6A. This voltage provides power to the control processor in standby mode, power to the PWM chips of the main source, and power to the PFC in operating mode. The TV switches from standby mode to operating mode by generating a voltage of 5.2V using a QB802 transistor switch. The supply voltage M_Vcc, in this case, is supplied to the PWM controllers ICP801S and ICM801. At the same time, the PFC and the main power supply are started.

Power supply "working"

The operating power supply is implemented using a forward converter circuit, which is made using a half-bridge circuit. This output source generates stabilized voltages:

24V (power supply for the backlight inverter), 13V, 12V and 5.3V for powering the lane.

Typical faults

Now let's look at the most popular defects of this power supply.

These include:

The material in this article is intended not only for owners of already rare televisions who want to restore their functionality, but also for those who want to understand the circuitry, structure and operating principle of switching power supplies. If you master the material in this article, then you can easily understand any circuit and operating principle of switching power supplies for household appliances, be it a TV, laptop or office equipment. And so let's get started...

Soviet-made televisions, the third generation ZUSTST, used switching power supplies - MP (power module).

Switching power supplies, depending on the TV model where they were used, were divided into three modifications - MP-1, MP-2 and MP-3-3. The power modules are assembled according to the same electrical circuit and differ only in the type of pulse transformer and the voltage rating of capacitor C27 at the output of the rectifier filter (see circuit diagram).

Functional diagram and principle of operation of a switching power supply for a TV set ZUSTST

Rice. 1. Functional diagram of the switching power supply for the ZUSTST TV:

1 - network rectifier; 2 - trigger pulse generator; 3 - pulse generator transistor, 4 - control cascade; 5 - stabilization device; 6 - protection device; 7 - pulse transformer of the TV power supply 3ust; 8 - rectifier; 9 - load

Let at the initial moment of time a pulse be generated in device 2, which will open the transistor of the pulse generator 3. At the same time, a linearly increasing sawtooth current will begin to flow through the winding of the pulse transformer with pins 19, 1. At the same time, energy will accumulate in the magnetic field of the transformer core, the value of which is determined by the open time of the pulse generator transistor. The secondary winding (pins 6, 12) of the pulse transformer is wound and connected in such a way that during the period of magnetic energy accumulation, a negative potential is applied to the anode of the VD diode and it is closed. After some time, control cascade 4 closes the pulse generator transistor. Since the current in the winding of transformer 7 cannot change instantly due to the accumulated magnetic energy, a self-induction emf of the opposite sign occurs. The VD diode opens, and the secondary winding current (pins 6, 12) increases sharply. Thus, if in the initial period of time the magnetic field was associated with the current that flowed through winding 1, 19, now it is created by the current of winding 6, 12. When all the energy accumulated during the closed state of switch 3 goes into the load, then in the secondary winding will reach zero.

From the above example we can conclude that by adjusting the duration of the open state of the transistor in a pulse generator, you can control the amount of energy that goes to the load. This adjustment is carried out using control cascade 4 using a feedback signal - the voltage at the terminals of winding 7, 13 of the pulse transformer. The feedback signal at the terminals of this winding is proportional to the voltage across the load 9.

If the voltage across the load decreases for some reason, the voltage supplied to the stabilization device 5 will also decrease. In turn, the stabilization device, through the control cascade, will begin to close the pulse generator transistor later. This will increase the time during which current will flow through winding 1, 19, and the amount of energy transferred to the load will accordingly increase.

The moment of the next opening of transistor 3 is determined by the stabilization device, where the signal coming from winding 13, 7 is analyzed, which allows you to automatically maintain the average value of the output DC voltage.

The use of a pulse transformer makes it possible to obtain voltages of different amplitudes in the windings and eliminates the galvanic connection between the circuits of secondary rectified voltages and the supply electrical network. Control stage 4 determines the range of pulses created by the generator and, if necessary, turns it off. The generator is switched off when the mains voltage drops below 150 V and the power consumption drops to 20 W, when the stabilization cascade stops functioning. When the stabilization cascade is not working, the pulse generator becomes uncontrollable, which can lead to the appearance of large current pulses in it and to the failure of the pulse generator transistor.

Schematic diagram of a switching power supply for a ZUSTST TV

Let's look at the circuit diagram of the MP-3-3 power module and the principle of its operation.

Rice. 2 Schematic diagram of a switching power supply for a ZUSTST TV, module MP-3-3

It includes a low-voltage rectifier (diodes VD4 - VD7), a trigger pulse shaper (VT3), a pulse generator (VT4), a stabilization device (VT1), a protection device (VT2), a pulse transformer T1 of the 3ustst power supply and rectifiers using diodes VD12 - VD15 with voltage stabilizer (VT5 - VT7).

The pulse generator is assembled according to a blocking generator circuit with collector-base connections on a VT4 transistor. When you turn on the TV, the constant voltage from the output of the low-voltage rectifier filter (capacitors C16, C19 and C20) through winding 19, 1 of transformer T1 is supplied to the collector of transistor VT4. At the same time, the mains voltage from diode VD7 through capacitors C11, C10 and resistor R11 charges capacitor C7, and also goes to the base of transistor VT2, where it is used in the device for protecting the power module from low voltage. When the voltage on capacitor C7, applied between the emitter and base 1 of unijunction transistor VT3, reaches a value of 3 V, transistor VT3 will open. Capacitor C7 is discharged through the circuit: emitter-base junction 1 of transistor VT3, emitter junction of transistor VT4, parallel connected, resistors R14 and R16, capacitor C7.

The discharge current of capacitor C7 opens transistor VT4 for a time of 10 - 15 μs, sufficient for the current in its collector circuit to increase to 3...4 A. The flow of collector current of transistor VT4 through the magnetization winding 19, 1 is accompanied by the accumulation of energy in the magnetic field of the core. After capacitor C7 has finished discharging, transistor VT4 closes. The cessation of the collector current causes the appearance of a self-induction EMF in the coils of transformer T1, which creates positive voltages at terminals 6, 8, 10, 5 and 7 of transformer T1. In this case, current flows through the diodes of half-wave rectifiers in the secondary circuits (VD12 - VD15).

With a positive voltage at terminals 5, 7 of transformer T1, capacitors C14 and C6 are charged, respectively, in the anode and control electrode circuits of thyristor VS1 and C2 in the emitter-base circuit of transistor VT1.

Capacitor C6 is charged through the circuit: pin 5 of transformer T1, diode VD11, resistor R19, capacitor C6, diode VD9, pin 3 of the transformer. Capacitor C14 is charged through the circuit: pin 5 of transformer T1, diode VD8, capacitor C14, pin 3 of transformer. Capacitor C2 is charged through the circuit: pin 7 of transformer T1, resistor R13, diode VD2, capacitor C2, pin 13 of the transformer.

The subsequent switching on and off of the blocking generator transistor VT4 is carried out similarly. Moreover, several such forced oscillations are sufficient to charge the capacitors in the secondary circuits. With the completion of charging of these capacitors, positive feedback begins to operate between the windings of the blocking generator connected to the collector (pins 1, 19) and the base (pins 3, 5) of the VT4 transistor. In this case, the blocking generator goes into self-oscillation mode, in which transistor VT4 will automatically open and close at a certain frequency.

During the open state of transistor VT4, its collector current flows from the plus of electrolytic capacitor C16 through the winding of transformer T1 with terminals 19, 1, the collector and emitter junctions of transistor VT4, parallel connected resistors R14, R16 to the minus of capacitor C16. Due to the presence of inductance in the circuit, the collector current increases according to a sawtooth law.

To eliminate the possibility of failure of transistor VT4 from overload, the resistance of resistors R14 and R16 is selected in such a way that when the collector current reaches 3.5 A, a voltage drop is created across them sufficient to open thyristor VS1. When the thyristor opens, capacitor C14 is discharged through the emitter junction of transistor VT4, resistors R14 and R16 connected in parallel, and open thyristor VS1. The discharge current of capacitor C14 is subtracted from the base current of transistor VT4, which leads to its premature closing.

Further processes in the operation of the blocking generator are determined by the state of the thyristor VS1, the earlier or later opening of which allows you to regulate the rise time of the sawtooth current and thereby the amount of energy stored in the transformer core.

The power module can operate in stabilization and short circuit mode.

The stabilization mode is determined by the operation of the DC amplifier (DC amplifier) assembled on transistor VT1 and thyristor VS1.

At a network voltage of 220 Volts, when the output voltages of the secondary power supplies reach rated values, the voltage on the winding of transformer T1 (pins 7, 13) increases to a value at which the constant voltage at the base of the transistor VT1, where it is supplied through the divider Rl - R3, becomes more negative than at the emitter, where it is completely transmitted. Transistor VT1 opens along the circuit: pin 7 of the transformer, R13, VD2, VD1, emitter and collector junctions of transistor VT1, R6, control electrode of the thyristor VS1, R14, R16, pin 13 of the transformer. This current, summed with the initial current of the control electrode of the thyristor VS1, opens it at the moment when the output voltage of the module reaches the nominal values, stopping the increase in the collector current.

By changing the voltage at the base of transistor VT1 with trimming resistor R2, you can adjust the voltage across resistor R10 and, therefore, change the opening moment of thyristor VS1 and the duration of the open state of transistor VT4, thereby setting the output voltage of the power supply.

When the load decreases (or the network voltage increases), the voltage at terminals 7, 13 of transformer T1 increases. At the same time, the negative voltage at the base increases in relation to the emitter of transistor VT1, causing an increase in the collector current and a voltage drop across resistor R10. This leads to earlier opening of thyristor VS1 and closing of transistor VT4. This reduces the power supplied to the load.

When the network voltage decreases, the voltage on the winding of transformer T1 and the base potential of transistor VT1 relative to the emitter become correspondingly lower. Now, due to a decrease in the voltage created by the collector current of transistor VT1 on resistor R10, thyristor VS1 opens at a later time and the amount of energy transferred to the secondary circuits increases. An important role in protecting transistor VT4 is played by the cascade on transistor VT2. When the network voltage decreases below 150 V, the voltage on the winding of transformer T1 with terminals 7, 13 is insufficient to open transistor VT1. In this case, the stabilization and protection device does not work, transistor VT4 becomes uncontrollable and the possibility of its failure is created due to exceeding the maximum permissible values of voltage, temperature, and current of the transistor. To prevent the failure of transistor VT4, it is necessary to block the operation of the blocking generator. The transistor VT2 intended for this purpose is connected in such a way that a constant voltage is supplied to its base from the divider R18, R4, and a pulsating voltage with a frequency of 50 Hz is supplied to the emitter, the amplitude of which is stabilized by the zener diode VD3. When the network voltage decreases, the voltage at the base of transistor VT2 decreases. Since the voltage at the emitter is stabilized, a decrease in the voltage at the base causes the transistor to open. Through the open transistor VT2, trapezoidal-shaped pulses from the diode VD7 arrive at the control electrode of the thyristor, opening it for a time determined by the duration of the trapezoidal pulse. This causes the blocking generator to stop working.

Short circuit mode occurs when there is a short circuit in the load of secondary power supplies. In this case, the power supply is started by triggering pulses from the trigger device assembled on transistor VT3, and turned off using thyristor VS1 according to the maximum collector current of transistor VT4. After the end of the triggering pulse, the device is not excited, since all the energy is spent in the short-circuited circuit.

After the short circuit is removed, the module enters stabilization mode.

Pulse voltage rectifiers connected to the secondary winding of transformer T1 are assembled according to a half-wave circuit.

The VD12 diode rectifier creates a voltage of 130 V to power the horizontal scanning circuit. The ripples of this voltage are smoothed out by the electrolytic capacitor C27. Resistor R22 eliminates the possibility of a significant increase in voltage at the rectifier output when the load is turned off.

A 28 V rectifier is assembled on the VD13 diode, designed to power the vertical scanning of a TV. Voltage filtering is provided by capacitor C28 and inductor L2.

A 15 V voltage rectifier for powering an audio amplifier is assembled using a VD15 diode and a SZO capacitor.

The 12 V voltage used in the color module (MC), radio channel module (MRK) and vertical scanning module (MS) is created by a rectifier using diode VD14 and capacitor C29. At the output of this rectifier, a compensating voltage regulator assembled on transistors is switched on. It consists of a regulating transistor VT5, a current amplifier VT6 and a control transistor VT7. The voltage from the output of the stabilizer through the divider R26, R27 is supplied to the base of the transistor VT7. Variable resistor R27 is designed to set the output voltage. In the emitter circuit of transistor VT7, the voltage at the output of the stabilizer is compared with the reference voltage at the zener diode VD16. The voltage from the collector VT7 through the amplifier on the transistor VT6 is supplied to the base of the transistor VT5, connected in series to the rectified current circuit. This leads to a change in its internal resistance, which, depending on whether the output voltage has increased or decreased, either increases or decreases. Capacitor C31 protects the stabilizer from excitation. Through resistor R23, voltage is supplied to the base of transistor VT7, which is necessary to open it when turned on and restore it after a short circuit. Choke L3 and capacitor C32 are an additional filter at the output of the stabilizer.

Capacitors C22 - C26 bypass rectifier diodes to reduce interference emitted by pulsed rectifiers into the electrical network.

Surge filter for power supply unit ZUSTST

The PFP power filter board is connected to the electrical network via connector X17 (A12), switch S1 in the TV control unit and mains fuses FU1 and FU2.

VPT-19 type fuses are used as mains fuses, the characteristics of which make it possible to provide significantly more reliable protection of television receivers in the event of malfunctions than PM type fuses.

The purpose of the barrier filter is .

On the power filter board there are barrier filter elements (C1, C2, SZ, inductor L1) (see circuit diagram).

Resistor R3 is designed to limit the current of the rectifier diodes when the TV is turned on. The posistor R1 and resistor R2 are elements of the kinescope mask demagnetization device.