Transformers, reference book. Dynamos. Switching Power Supply For Screwdriver - Power supplies (switching) - Power supplies Power supply device made of TPI 4 3

Pulse power transformers (TPI) are used in pulse power supply devices for household and office equipment with intermediate conversion of the supply voltage of 127 or 220 V with a frequency of 50 Hz into rectangular pulses with a repetition frequency of up to 30 kHz, made in the form of modules or power supplies: PSU, MP-1, MP-2, MP-Z, MP-403, etc. The modules have the same circuit and differ only in the type of pulse transformer used and the rating of one of the capacitors at the filter output, which is determined by the features of the model in which they are used.
Powerful TPI transformers for switching power supplies are used for decoupling and transferring energy to secondary circuits. Energy storage in these transformers is undesirable. When designing such transformers, as a first step it is necessary to determine the amplitude of oscillations of the magnetic induction of the DV in a steady state. The transformer must be designed to operate at the highest possible DV value, which makes it possible to have a smaller number of turns in the magnetizing winding, increase the rated power and reduce leakage inductance. In practice, the DV value can be limited either by the saturation induction of the core B s, or by losses in the transformer magnetic circuit.
In most full-bridge, half-bridge, and full-wave (balanced) midpoint circuits, the transformer is driven symmetrically. In this case, the value of magnetic induction changes symmetrically relative to the zero of the magnetization characteristic, which makes it possible to have a theoretical maximum value of DV equal to twice the value of saturation induction Bs. In most single-cycle circuits used, for example, in single-cycle converters, the magnetic induction fluctuates completely within the first quadrant of the magnetization characteristic from the residual induction Br to the saturation induction Bs, limiting the theoretical maximum of the DV to the value (Bs - BR). This means that if the DV is not limited by losses in the magnetic circuit (usually at frequencies below 50 ... 100 kHz), single-ended circuits will require a larger transformer at the same output power.
In voltage-fed circuits (which includes all buck regulator circuits), according to Faraday's law, the DV value is determined by the volt-second product of the primary winding. In steady state, the volt-second product on the primary winding is set at a constant level. The range of oscillations of magnetic induction is thus also constant.
However, with the usual duty cycle control method, which is used by most ICs for switching regulators, at startup and during a sharp increase in load current, the value of DV can reach twice the value in the steady state. Therefore, to prevent the core from becoming saturated during transients, the steady-state value of DV should be half the theoretical maximum However, if a microcircuit is used that allows you to control the value of the volt-second product (circuits that monitor input voltage disturbances), then the maximum value of the volt-second product is fixed at a level slightly higher than the steady state. This allows you to increase the value of DV and improves the performance of the transformer.
The value of saturation induction B s for most ferrites for strong magnetic fields such as 2500NMS exceeds 0.3 Tesla. In push-pull voltage-fed circuits, the magnitude of the increment in the induction of the DV is usually limited to a value of 0.3 Tesla. As the excitation frequency increases to 50 kHz, the losses in the magnetic circuit approach the losses in the wires. An increase in losses in the magnetic circuit at frequencies above 50 kHz leads to a decrease in the DV value.
In single-cycle circuits without fixing the volt-second product for cores with (Bs - Br) equal to 0.2 T, and taking into account transient processes, the steady-state value of DV is limited to only 0.1 T. Losses in the magnetic circuit at a frequency of 50 kHz will be insignificant due to the small amplitude of magnetic induction fluctuations. In circuits with a fixed value of the volt-second product, the DV value can take values ​​up to 0.2 T, which makes it possible to significantly reduce the overall dimensions of a pulse transformer.
In current-driven power supply circuits (boost converters and current-controlled buck regulators on coupled inductors), the DV value is determined by the volt-second product on the secondary winding at a fixed output voltage. Since the output volt-second product is independent of changes in input voltage, current-fed circuits can operate at DV values ​​close to the theoretical maximum (ignoring core losses) without having to limit the volt-second product. .
At frequencies above 50. The 100 kHz DV value is usually limited by losses in the magnetic circuit.
The second step when designing powerful transformers for switching power supplies is to make the correct choice of the type of core that will not saturate at a given volt-second product and will provide acceptable losses in the magnetic core and windings. To do this, you can use an iterative calculation process, but the formulas given below ( 3 1) and (3 2) make it possible to calculate the approximate value of the product of core areas S o S c (the product of the core window area S o and the cross-sectional area of ​​the magnetic core S c) Formula (3 1) is used when the value of the DV is limited by saturation, and the formula ( 3.2) - when the DV value is limited by losses in the magnetic circuit, in doubtful cases, both values ​​are calculated and the largest of the reference data tables is used for various cores; the type of core for which the product S o S c exceeds the calculated value is selected.

Where
Rin = Rout/l = (output power/efficiency);
K is a coefficient that takes into account the degree of use of the core window, the area of ​​the primary winding and the design factor (see Table 3 1); fp - transformer operating frequency


For most ferrites for strong magnetic fields, the hysteresis coefficient is K k = 4 10 5, and the eddy current loss coefficient is K w = 4 10 10.
Formulas (3.1) and (3.2) assume that the windings occupy 40% of the core window area, the ratio between the areas of the primary and secondary windings corresponds to the same current density in both windings, equal to 420 A/cm2, and that the total losses in the magnetic core and windings lead to a temperature difference in the heating zone of 30 °C during natural cooling.
As a third step when designing high-power transformers for switching power supplies, it is necessary to calculate the windings of the pulse transformer.
In table 3.2 shows unified power supply transformers of the TPI type used in television receivers.








Winding data of TPI type transformers operating in pulsed power supplies for stationary and portable television receivers are given in Table 3. 3 Schematic electrical diagrams of TPI transformers are shown in Fig. 3. 1

Rice. 7.20. Schematic diagram of a transformer type TS-360M D71YA for powering the TV LPTC-59-1I

short interturn circuit. Corrosion of small diameter winding wires leads to their breakage.

The design of transformers of the TS-360M type ensures reliable operation in TV power supplies without breaks in the windings and other damage, as well as without corrosion on metal parts under repeated cyclic exposure to temperatures, high humidity and mechanical loads specified in the operating conditions. Modern new technological processes for manufacturing transformers and impregnation of windings with sealing compounds increase the service life of both the transformers themselves and the equipment as a whole.

Transformers are installed on the metal chassis of the TV, secured with four screws and grounded.

The winding data of the windings and electrical parameters of transformers of the TS-360M type are given in Table. 7.11 and 7.12. The electrical circuit diagram of the transformer is shown in Fig. 7.20.

The insulation resistance between the windings, as well as between the windings and the metal parts of the transformer under normal conditions is at least 100 MOhm.

7.2. Pulse power transformers

In modern models of television receivers, pulse power transformers operating as part of power supplies or power modules are widely used, providing the advantages discussed in the chapter on unified pulse power transformers. Television pulse transformers have a number of significant features in terms of design and technical characteristics.

Switching network units and power modules for television receivers, powered by an AC mains voltage of 127 or 220 V with a frequency of 50 Hz, are used to obtain AC and DC voltages necessary to power all functional components of the TV. These power supplies and modules differ from the traditional ones considered in lower material consumption, higher power density and higher efficiency, which is due to the absence of TC type power transformers operating at a frequency of 50 Hz and the use of secondary switching stabilizers

stresses instead of continuous compensation ones.

In switching network power supplies, the alternating mains voltage is converted into a relatively high direct current voltage using a transformerless rectifier with an appropriate filter. The voltage from the filter output is supplied to the input of a pulse voltage stabilizer, which reduces the voltage from 220 V to 100... 150 V and stabilizes it. The stabilizer powers an inverter, the output voltage of which has the form of a rectangular pulse with an increased frequency of up to 40 kHz.

A filter rectifier converts this voltage to DC voltage. The alternating voltage is obtained directly from the inverter. The inverter's high-frequency pulse transformer eliminates galvanic coupling between the power supply output and the power supply network. If there are no increased requirements for the stability of the unit's output voltages, then a voltage stabilizer is not used. Depending on the specific requirements for the power supply, it may contain various additional functional units and circuits, one way or another connected with the pulse transformer: output voltage stabilizer, protection device against overloads and emergency modes, initial start-up circuits, interference suppression circuits, etc. TV power supplies typically use inverters, the switching frequency of which is determined by the saturation of the power transformer. In these cases, inverters with two transformers are used.

The power supply with an output power of 180 VA at a load current of 3.5 A and a conversion frequency of 27 kHz uses two pulse transformers on ring magnetic cores. The first transformer is made on two ring magnetic cores K31x 18.5x7 from ferrite grade 2000NN. Winding I contains 82 turns of PEV-2 0.5 wire, winding P - 16 + 16 turns of PEV-2 1.0 wire, winding Sh - 2 turns of PEV-2 0.3 wire. The second transformer is made on a ring magnetic core K10X6X5 from ferrite grade 2000NN. The windings are made of PEV-2 0.3 wire. Winding I contains ten turns, windings P and P1 - six turns each. Windings I of both transformers are placed evenly along the magnetic circuit, winding P1 of the first transformer is placed in a place not occupied by winding P. The windings are insulated among themselves with varnished cloth tape. The insulation between windings I and II of the first transformer is three-layer, and between the remaining windings it is single-layer.

In the power supply: rated load power 100 VA, output voltage not less than plusmn; 27 V at rated output power and not less than plusmn; 31 V at output power 10 VA, efficiency - approximately 85% at rated output power, frequency conversion 25...28 kHz, three pulse transformers are used. The first transformer is made on a K10X6X4 ring magnetic core made of 2000NMS grade ferrite, the windings are made of PEV-2 0.31 wire. Winding I contains eight turns, the remaining windings have four turns each. The second transformer is made on a K10X6X4 ring magnetic core made of ferrite grade 2000NMZ, the windings are wound with PEV-2 0.41 wire. Winding I consists of one turn, winding II contains two turns. The third transformer has a Sh7x7 type core made of ZOOONMS ferrite. Winding I contains 60x2 turns (2 sections), and winding II contains 20 turns of PEV-2 0.31 wire, windings III and IV contain 24 turns of PEV-2 0.41 wire each. Windings II, III, IV are located between sections of winding I. Under the windings

ni and IV and screens in the form of a closed coil of copper foil are placed above them. The magnetic core of the third transformer is galvanically connected to the positive pole of the primary rectifier. This transformer design is necessary to suppress interference, the source of which is the powerful inverter of the unit.

The use of pulse transformers ensures increased reliability and durability, reduced overall dimensions and weight of power supply units and modules. But it should also be noted that switching stabilizers used in TV power supplies have the following disadvantages: a more complex control device, increased noise levels, radio interference and output voltage ripple, and at the same time worse dynamic characteristics.

In master oscillators of horizontal or vertical scanning, operating according to the blocking oscillator circuit.

Pulse transformers and autotransformers are used. These transformers (autotransformers) are elements with strong inductive feedback. In the technical literature, pulse transformers and autotransformers for horizontal scanning are abbreviated as BTS and BATS; for personnel scanning - VTK and TBK. Pulse transformers VTK and TBK are practically no different in design from other transformers. Transformers are manufactured for both volumetric and printed circuit mounting.

Pulse transformers of types TPI-2, TPI-3, TPI-4-2, TPI-5, etc. are used in power supplies and modules.

Winding data for transformers operating in pulse mode, used in stationary and portable television receivers, are given in Table. 7.13.

Table 7.13. Wet data of pulse transformers used in televisions

Designation

Brand and diameter

typenomshala

transformer windings

wires, mm

permanent

transformer

Magnetizing

PEVTL-2 0.45

PEVTL-2 0.45

Stabilization

Pitch 2.5 mm

PEVTL-2 0.45

Positive about-

Private in

PEVTL-2 0.45

military communications

Rectifiers with on-

Private in

yarns, V:

two wires

PEVTL-2 0.45

PEVTL-2 0.45

PEVTL-2 0.45

PEVTL-2 0.45

PEVTL-2 0.45

Magnetization Same

Private in two wires

PEVTL-2 0.45

PEVTL-2 0.45

Stabilization

PEVTL-2 0.45

Rectifiers with on-

yarns, V:

PEVTL-2 0.45

Private in two wires

PEVTL-2 0.45

PEVTL-2 0.45

PEVTL-2 0.45

Foil one layer

Positive about-

PEVTL-2 0.45

military communications

or Ш (УШ)

Magnetization

Private in two wires

PEVTL-2 0.45

Magnetization

PEVTL-2 0.45

Stabilization

Private, pitch 2.5 mm

PEVTL-2 0.45

Rectifiers with on-

yarn, V:

PEVTL-2 0.45

Private in two wires

PEVTL-2 0.45

PEVTL-2 0.45

PEVTL-2 0.45

Continuation of the table. 7.13

Designation

Name

Brand and diameter

Resistance

typonokmnala

wires, mm

permanent

transformer

Positive about-

PEVTL-2 0.45

military communications

Magnetization

Private in

PEVTL-2 0.45

two wires

PEVTL-2 0.45

Stabilization

PEVTL-2 0.25

Weekend rectifier

voltage

PEVTL-2 0.45

Private in

PEVTL-2 0.45

two wires

Private in

PEVTL-2 0.45

two wires

PEVTL-2 0.45

Positive about-

PEVTL-2 0.45

military communications

Primary

Secondary

12 plates

Primary

Universal

Secondary

Primary

Secondary

Primary

Recuperative

Primary

Feedback

Day off

Primary network

Private in

PEVTL-2 0.5

Rice. 1. Network filter board diagram.

Soviet TVs Horizon Ts-257 used a switching power supply with intermediate conversion of the mains voltage with a frequency of 50 Hz into rectangular pulses with a repetition frequency of 20...30 kHz and their subsequent rectification. The output voltages are stabilized by changing the duration and repetition rate of the pulses.

The source is made in the form of two functionally complete units: a power module and a network filter board. The module provides isolation of the TV chassis from the network, and elements galvanically connected to the network are covered with screens that restrict access to them.

Main technical characteristics of a switching power supply

  • Maximum output power, W........100
  • Efficiency..........0,8
  • Limits for changes in network voltage, V......... 176...242
  • Instability of output voltages, %, no more..........1
  • Rated values ​​of load current, mA, voltage sources, V:
    135     ....................500
    28 ....................340
    15 ..........700
    12 ..........600
  • Weight, kg ...................1

Rice. 2 Schematic diagram of the power module.

It contains a mains voltage rectifier (VD4-VD7), a starting stage (VT3), stabilization units (VT1) and blocking 4VT2), a converter (VT4, VS1, T1), four half-wave output voltage rectifiers (VD12-VD15) and a compensation voltage stabilizer 12 V (VT5-VT7).

When the TV is turned on, the mains voltage is supplied to the rectifier bridge VD4-VD7 through a limiting resistor and noise suppression circuits located on the power filter board. The voltage rectified by it passes through the magnetization winding I of pulse transformer T1 to the collector of transistor VT4. The presence of this voltage on capacitors C16, C19, C20 is indicated by LED HL1.

Positive mains voltage pulses through capacitors C10, C11 and resistor R11 charge capacitor C7 of the trigger stage. As soon as the voltage between the emitter and base 1 of unijunction transistor VT3 reaches 3 V, it opens and capacitor C7 is quickly discharged through its emitter-base 1 junction, the emitter junction of transistor VT4 and resistors R14, R16. As a result, transistor VT4 opens for 10...14 μs. During this time, the current in the magnetization winding I increases to 3...4 A, and then, when transistor VT4 is closed, it decreases. The pulse voltages arising on windings II and V are rectified by diodes VD2, VD8, VD9, VD11 and charge capacitors C2, C6, C14: the first of them is charged from winding II, the other two are charged from winding V. With each subsequent switching on and off of the transistor VT4 recharges the capacitors.

As for the secondary circuits, at the initial moment after turning on the TV, the capacitors C27-SZO are discharged, and the power module operates in a mode close to a short circuit. In this case, all the energy accumulated in transformer T1 enters the secondary circuits, and there is no self-oscillating process in the module.

Upon completion of charging of the capacitors, oscillations of the residual energy of the magnetic field in transformer T1 create such a positive feedback voltage in the winding V, which leads to the occurrence of a self-oscillating process.

In this mode, transistor VT4 opens with positive feedback voltage, and closes with voltage on capacitor C14 supplied through thyristor VS1. It happens like this. The linearly increasing current of the opened transistor VT4 creates a voltage drop across resistors R14 and R16, which in positive polarity through cell R10C3 is supplied to the control electrode of thyristor VS1. At the moment determined by the operating threshold, the thyristor opens, the voltage on capacitor C14 is applied in reverse polarity to the emitter junction of transistor VT4, and it closes.

Thus, turning on the thyristor sets the duration of the sawtooth pulse of the collector current of transistor VT4 and, accordingly, the amount of energy given to the secondary circuits.

When the output voltages of the module reach nominal values, capacitor C2 is charged so much that the voltage removed from the divider R1R2R3 becomes greater than the voltage on the zener diode VD1 and the transistor VT1 of the stabilization unit opens. Part of its collector current is summed in the circuit of the thyristor control electrode with the initial bias current created by the voltage on capacitor C6 and the current generated by the voltage on resistors R14 and R16. As a result, the thyristor opens earlier and the collector current of transistor VT4 decreases to 2...2.5 A.

When the network voltage increases or the load current decreases, the voltages on all windings of the transformer increase, and therefore the voltage on capacitor C2 increases. This leads to an increase in the collector current of transistor VT1, earlier opening of thyristor VS1 and closing of transistor VT4, and, consequently, to a decrease in the power supplied to the load. Conversely, when the network voltage decreases or the load current increases, the power transferred to the load increases. Thus, all output voltages are stabilized at once. Trimmer resistor R2 sets their initial values.

In the event of a short circuit of one of the module outputs, self-oscillations are disrupted. As a result, transistor VT4 is opened only by the triggering cascade on transistor VT3 and closed by thyristor VS1 when the collector current of transistor VT4 reaches a value of 3.5...4 A. Packets of pulses appear on the windings of the transformer, following at the frequency of the supply network and a filling frequency of about 1 kHz. In this mode, the module can operate for a long time, since the collector current of transistor VT4 is limited to a permissible value of 4 A, and the currents in the output circuits are limited to safe values.

In order to prevent large current surges through the transistor VT4 at an excessively low network voltage (140... 160 V) and, therefore, in case of unstable operation of the thyristor VS1, a blocking unit is provided, which in this case turns off the module. The base of the transistor VT2 of this node receives a direct voltage proportional to the rectified mains voltage from the divider R18R4, and the emitter receives a pulse voltage with a frequency of 50 Hz and an amplitude determined by the zener diode VD3. Their ratio is chosen such that at the specified network voltage, transistor VT2 opens and thyristor VS1 opens with collector current pulses. The self-oscillatory process stops. As the network voltage increases, the transistor closes and does not affect the operation of the converter. To reduce the instability of the 12 V output voltage, a compensation voltage stabilizer on transistors (VT5-VT7) with continuous regulation is used. Its feature is current limitation during a short circuit in the load.

In order to reduce the influence on other circuits, the output stage of the audio channel is powered from a separate winding III.

IN pulse transformer TPI-3 (T1) uses magnetic core M3000NMS Ш12Х20Х15 with an air gap of 1.3 mm on the middle rod.

Rice. 3. Layout of the windings of the TPI-3 pulse transformer.

Winding data of the TPI-3 transformer switching power supply are given:

All windings are made with PEVTL 0.45 wire. In order to uniformly distribute the magnetic field over the secondary windings of the pulse transformer and increase the coupling coefficient, winding I is divided into two parts, located in the first and last layers and connected in series. Stabilization winding II is made with a pitch of 1.1 mm in one layer. Winding III and sections 1 - 11 (I), 12-18 (IV) are wound in two wires. To reduce the level of radiated interference, four electrostatic screens were introduced between the windings and a short-circuited screen on top of the magnetic conductor.

The power filter board (Fig. 1) contains elements of the L1C1-SZ barrier filter, a current-limiting resistor R1 and a device for automatic demagnetization of the kinescope mask on the thermistor R2 with a positive TKS. The latter provides a maximum amplitude of the demagnetization current of up to 6 A with a smooth decline within 2...3 s.

Attention!!! When working with the power module and TV, you must remember that the elements of the power filter board and some of the module parts are under mains voltage. Therefore, it is possible to repair and check the power module and filter board under voltage only when they are connected to the network through an isolation transformer.

End of table. 2.2 Number w IV IVa IV6 IV6 IV6 V VI Winding Name Positive feedback Rectifiers 125, 24, 18 V Rectifier 15 V Rectifier 12 V Conclusions 11 6-12 including: 6-10 10-4 4-8 8-12 14 -18 16-20 Number of turns 16 74 54 7 5 12 10 10 Wire brand PEVTL-0.355 ZZIM PEVTL-0.355 PEVTL-0.355 Winding type Ordinary in three wires Ordinary in two wires, two layers Ordinary in two wires Same -“- Ordinary in four wires The same Resistance, Ohm 0.2 1.2 0.9 0.2 0.2 0.2 0.2 0.2 Note. Transformers TPI-3, TPI 4 2, TPI-4-3, TPI-5 are made on a magnetic core M300NMS Ш12Х20Х15 with an air gap of 1.3 mm in the middle rod, transformer TPI-8-1 is made on a closed magnetic core M300NMS-2 Ш12Х20Х21 with an air gap a gap of 1.37 mm in the middle rod of any electrical alterations, but at the same time, connector X2 of the MP-4-6 module must be shifted to the left by one contact (its second contact becomes like the first contact) or when connecting MP-44-3 instead of MP-3, the fourth contact of connector X2 becomes, as it were, the first contact.

In table 2 2 shows the winding data of pulse power transformers.

The general view, overall dimensions and layout of the printed circuit board for installing pulse power transformers are shown in Fig. 2.16.

Rice. 2.16. General view, overall dimensions and layout of the printed circuit board for installing pulse power transformers. A feature of the SMPS is that they cannot be turned on without a load. In other words, when repairing the MP, it must be connected to the TV or load equivalents must be connected to the MP outputs. The circuit diagram for connecting load equivalents is shown in Fig. 2 17.

The following equivalent loads must be installed in the circuit: R1-resistor with a resistance of 20 Ohms ±5%, with a power of at least 10 W; R2—resistor with a resistance of 36 Ohms ±5%, power of at least 15 W; R3 - resistor with a resistance of 82 Ohms ±5%, power of at least 15 W; R4 -RPSh 0.6 A =1000 Ohm; in amateur radio practice, instead of a rheostat, a 220 V electric lamp with a power of at least 25 W or a 127 V lamp with a power of 40 W is often used; Rice. 2.17. Schematic diagram of connecting load equivalents to the R5 power module - a resistor with a resistance of 3.6 Ohms, a power of at least 50 W; C1 - capacitor type K50-35-25 V, 470 μF; C2 - capacitor type K50-35-25 V, 1000 μF; SZ capacitor type K50-35-40 V, 470 µF.

Load currents should be: for a 12 V circuit 1„o„=0.6 A; on a circuit 15 V 1nom = 0.4 A (minimum current 0.015 A), maximum 1 A); along a 28 V circuit 1„OM=0.35 A; along the circuit 125... 135 V 1„Ohm = 0.4 A (minimum current 0.3 A, maximum 0.5 A).

A switching power supply has circuits connected directly to the mains voltage. Therefore, when repairing an MP, it must be connected to the network via an isolation transformer.

The danger zone on the MP board from the printing side is indicated by hatching with solid lines.

Replace faulty elements in the module only after turning off the TV and discharging the oxide capacitors in the filter circuits of the mains rectifier.

Repair of the MP should begin with removing its protective covers, removing dust and dirt, and visually checking for installation defects and radioelements with external damage. 2.6, Possible malfunctions and methods for their elimination The principle of construction of the basic models of 4USCT TVs is the same, the output voltages of the secondary switching power supplies are also almost the same and are designed to power the same sections of the TV circuit. Therefore, at its core, the external manifestation of malfunctions, their possible39

A screwdriver or cordless drill is a very convenient tool, but there is also a significant drawback - with active use, the battery discharges very quickly - in a few tens of minutes, and it takes hours to charge. Even having a spare battery doesn't help. A good way out when working indoors with a working 220V power supply would be an external source for powering the screwdriver from the mains, which could be used instead of a battery. But, unfortunately, specialized sources for powering screwdrivers from the mains are not commercially produced (only chargers for batteries, which cannot be used as a mains source due to insufficient output current, but only as a charger).

In the literature and on the Internet there are proposals to use car chargers based on a power transformer, as well as power supplies from personal computers and for halogen lighting lamps, as a power source for a screwdriver with a rated voltage of 13V. All of these are probably good options, but without pretending to be original, I suggest making a special power supply yourself. Moreover, based on the circuit I have given, you can make a power supply for another purpose.

And so, the source diagram is shown in the figure in the text of the article.

This is a classic flyback AC-DC converter based on the UC3842 PWM generator.

The voltage from the network is supplied to the bridge using diodes VD1-VD4. A constant voltage of about 300V is released at capacitor C1. This voltage powers a pulse generator with transformer T1 at the output. Initially, the triggering voltage is supplied to power pin 7 of IC A1 through resistor R1. The pulse generator of the microcircuit is turned on and produces pulses at pin 6. They are fed to the gate of the powerful field-effect transistor VT1 in the drain circuit of which the primary winding of the pulse transformer T1 is connected. The transformer begins to operate and secondary voltages appear on the secondary windings. The voltage from winding 7-11 is rectified by diode VD6 and used
to power microcircuit A1, which, having switched to constant generation mode, begins to consume current that the starting power supply on resistor R1 is not capable of supporting. Therefore, if the diode VD6 malfunctions, the source pulsates - through R1, capacitor C4 is charged to the voltage required to start the microcircuit generator, and when the generator starts, the increased current C4 discharges, and generation stops. Then the process is repeated. If VD6 is working properly, immediately after startup the circuit switches to power from winding 11 -7 of transformer T1.

Secondary voltage 14V (at idle 15V, under full load 11V) is taken from winding 14-18. It is rectified by diode VD7 and smoothed by capacitor C7.
Unlike the standard circuit, a protection circuit for the output switching transistor VT1 from increased drain-source current is not used here. And the protection input, pin 3 of the microcircuit, is simply connected to the common negative of the power supply. The reason for this decision is that the author does not have the necessary low-resistance resistor (after all, you have to make one from what is available). So the transistor here is not protected from overcurrent, which of course is not very good. However, the scheme has been working for a long time without this protection. However, if desired, you can easily make protection by following the typical connection diagram of the UC3842 IC.

Details. Pulse transformer T1 is a ready-made TPI-8-1 from the power supply module MP-403 of a domestic color TV of type 3-USTST or 4-USTST. These TVs are now often dismantled or thrown away altogether. Yes, and TPI-8-1 transformers are available for sale. In the diagram, the terminal numbers of the transformer windings are shown according to the markings on it and on the circuit diagram of the MP-403 power module.

The TPI-8-1 transformer has other secondary windings, so you can get another 14V using winding 16-20 (or 28V by connecting 16-20 and 14-18 in series), 18V from winding 12-8, 29V from winding 12- 10 and 125V from winding 12-6. In this way, you can obtain a power source to power any electronic device, for example, an ULF with a preliminary stage.

However, the matter is limited to this, because rewinding the TPI-8-1 transformer is a rather thankless job. Its core is tightly glued and when you try to separate it, it breaks not where you expect. So, in general, you won’t be able to get any voltage from this unit, except perhaps with the help of a secondary step-down stabilizer.

The IRF840 transistor can be replaced with an IRFBC40 (which is basically the same), or with a BUZ90, KP707V2.

The KD202 diode can be replaced with any more modern rectifier diode with a direct current of at least 10A.

As a radiator for transistor VT1, you can use the key transistor radiator available on the MP-403 module board, modifying it slightly.


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