Hello student. Push-pull circuits and the basics of their calculation Circuits of push-pull voltage converters for powering a millivoltmeter

A push-pull inverter built on the basis of an emitter power follower is a push-pull pulsed current source with low weight and small dimensions. Used to charge batteries at a stable voltage. The maximum current set at the beginning of the charge decreases towards the end to the state of buffer charging - this is close in characteristics to charging batteries in cars.
The power source uses radio components of outdated power supplies for computers and monitors.

The main functional parts of the charger circuit:
1. Input protection circuits against overloads and short circuits.
2. Network noise suppression two-section filter.
3. Network rectifier.
3. High voltage smoothing filter.
4. Power inverter based on an emitter follower on bipolar transistors.
5. Circuits of transmission and formation of a voltage stabilization feedback signal.
6. Rectangular pulse generator.
7. Output current regulator.
8. Secondary voltage rectifier.
9. Protection and load indication circuits.

In the push-pull inverter circuit, a triple voltage conversion takes place: the alternating voltage of the network is rectified and smoothed to direct current, then it is converted into a pulse voltage, with a frequency of up to several tens of kilohertz, transformed into a low-voltage circuit and rectified. The secondary circuit voltage is used to charge the batteries.
The negative feedback circuit allows you to charge batteries or power the load with a stabilized voltage.
The push-pull circuit of the inverter contains transistors, reduced in comparison with the flyback circuit, power and voltage.
The feedback circuits on the optocoupler and the pulse transformer galvanically separate the inverter's high mains voltage from the low voltage circuits.
The low voltage assembly is equipped with powerful avalanche diodes in the assembly, indication of low voltage and load current.
The output voltage is stabilized by introducing a negative voltage feedback circuit into the circuit, and the increase in the temperature of the transistors from overheating is controlled by a thermistor.

Main technical characteristics:

Supply voltage. B - 165...240
Output voltage. B - 12...16
Load output current. A - 10
Conversion frequency, kHz - 22...47

Scheme

The input noise suppression filter consists of a two-winding inductor T2 (Fig. 1) and capacitors C13, C14, which reduce the converter's interference to the network and eliminate the possibility of impulse noise from the power supply.

The mains voltage from the filter is supplied to the VD7 rectifier through the FU1 fuse and the SA1 mains switch.

The mains rectifier is supplemented with a smoothing filter from high-capacity capacitors C8, C9, shunted by resistors R12, R13 to equalize the voltages. Thermistor RK2 limits the charge current of capacitors when mains voltage is applied.
The high-frequency transformer L of the inverter is connected with one output to the midpoint of the connection of capacitors C8, C9, and the second - to the connection point of the transistors of the push-pull converter, through the isolation capacitor C7.

The introduction of the resistor R15 into the oscillatory circuit reduces the quality factor of the transformer winding and accelerates the damping of the oscillatory process.
Transistors VT2, VT3 are shunted by high-speed diodes VD4, VD5 from breakdown by reverse currents.

The separating capacitor C7 eliminates the magnetization of the magnetic circuit of the transformer T1 of the inverter, with a spread in the parameters of the capacitors C7, C8 and incorrect installation of half the supply voltage at the midpoint of the connection of transistors VT2, VT3.
Due to the low transfer coefficient of powerful inverter transistors, a bipolar transistor VT1 is added to the circuit.

Setting half of the power supply voltage at the junction point of transistors VT2, VT3 is performed by selecting the resistance value of the resistor R8.

Diode VD3 accelerates the switching of the emitter follower on transistors VT1, VT2.
The load of the emitter follower is the VT3 transistor, which operates in static mode with a grounded, alternating current, base. For direct current, a small bias is applied to the base of the transistor VT3, through the resistor R8, to create a voltage on the collector close to half the supply voltage.

The master oscillator is made on an analog timer DA1.
The microcircuit contains: two operational amplifiers working as comparators; RC trigger; an output amplifier and a key transistor for discharging an external time-charging capacitor C1.

From the output 3 of the generator of the DA1 chip, rectangular pulses are taken. At a high level at output 3 DA1, the pulse through the integrated RC circuit R5, C4 enters the base of the transistor VT1 of the composite emitter follower, the transistor opens and opens a powerful bipolar transistor VT2. Capacitor C7 is charged from the positive rail of the power supply. A current pulse will appear in the primary circuit of transformer T1. At the end of the positive pulse from pin 3 of the DA1 microcircuit, the internal trigger pin 7 of DA1 switches to a conductive state relative to the minus power supply of the DA1 microcircuit, the base of the transistor VT1 closes to the minus power supply of the microcircuit, capacitor C4 is also rapidly discharged. The emitter follower transistors are closed and the capacitor C7 is discharged through the open transistor VT3.

To correctly match the generator pulses to the base-emitter junction of the inverter follower VT1, VT2, the generator is powered from the positive bus of the high-voltage power source through a voltage-limiting resistor R10, stabilized by the zener diode VD2. The minus of the power supply of the microcircuit is taken from the middle point of the connection of transistors VT2, VT3. With the arrival of the subsequent pulse from the generator to the input of the emitter follower, transistors VT1, VT2 open and the process repeats.

A continuous sequence of pulses in the primary winding of the high-frequency transformer T1 activates the appearance of high-frequency voltage in the secondary winding of the transformer and current at the load KhTZ, KhT4.
Pins 2 and 6 of the comparator input of the DA1 microcircuit switch the internal trigger depending on the voltage level on the capacitor C1, the charge time of which depends on the ratings of the RC circuit R1, R2, C1.

Pin 5 of DA1 allows direct access to the divider point with level 2/3 of the supply voltage, which is the reference for the operation of the upper comparator. Using this pin allows you to change this level to get schema modifications.
The constructive use of this output in the negative feedback circuit allows you to implement the stabilization of the output voltage.

The voltage from the load through the thermistor RK1 is supplied to the setting variable resistor R14, which regulates the voltage at the load. When the voltage at the KhTZ, XT4 terminals increases, the amplifier on the DA2 parallel stabilizer increases the brightness of the U1 optocoupler LED, the optocoupler transistor opens and reduces the voltage at pin 5 of DA1. The frequency of the generator increases. The duration of the output pulses is reduced, which leads to a decrease in the voltage at the load.

The DA2 parallel stabilizer serves as an amplifier for the voltage mismatch signal at the load and operates in a linear mode. The installation of a transistor amplifier in this circuit is undesirable due to the spread of parameters and the significant effect of external temperature.

An increase in the temperature of the key transistors VT2, VT3 of the inverter will lead to a decrease in the resistance of the thermistor RK1 and to a decrease in the duty cycle and power in the load.
The power supply of the DA1 chip is made from the high voltage of the inverter through the voltage limiter on the resistor R10 and is stabilized by the VD2 diode.

The rectifier of the secondary circuit is made on a powerful pair of VD6 avalanche diodes assembled in an assembly, the indication of the polarity of the presence of a secondary voltage is indicated by the HL1 LED. Capacitor SU smooths out voltage ripples in low-voltage circuits.

Printed circuit board, details
The printed circuit board of the electronic circuit consists of two parts (Fig. 2 and Fig. 3), connected by conductors.
The 7555 low power timer DA1 will be replaced by the 555 micropower timer.
Network diode bridge VD7 for voltage not lower than 400 V and current more than 3 A, low-voltage rectifier
VD6 for a voltage of at least 50 V and a current of at least 20 A will be replaced with an S40D45C assembly from computer power supplies.
Transistors VT2.VT3 are suitable for a voltage of at least 300 V and a current of more than 3 A - types 2SC2555, 2625, 3036, 3306, 13009 with installation on a radiator with insulating gaskets.

Aluminum oxide capacitors from Nikon or REC.
Optocouplers - from the LTV817, PC816 series.
Transformer T1 is used without rewinding from the AT / TX computer power supply. The 1T1 winding is 38 turns of wire with a diameter of 0.8 mm, the secondary has two windings of 7.5 turns each, with a cross section of 4 * 0.31 mm in a bundle.
Transformer T2 is a two-winding mains filter choke.
Coil L1 - filter choke, 10 turns of wire with a diameter of 1 mm on a 20 mm ferrite ring.

Adjustment

The adjustment of the circuit consists in checking the power modes. With resistor R8, set a voltage on the emitter VT3 equal to half the voltage of the power source - about 150 V.

It is necessary to power the inverter circuit during testing through a 220/220 V * 100 W transition transformer to eliminate possible electrical shock.
Before starting, a 220 V * 100 W light bulb is connected to the mains circuit instead of the FU1 fuse, instead of a load, connect a 12-24 V * 50 candles car light bulb.

The increased brightness of the mains light bulb and the absence of the glow of the light bulb in the load indicate a malfunction in the circuit.
With a weak glow of the mains lamp and a bright glow of the load lamp, with the presence of brightness control, the working state of the circuit is confirmed.

After a short operation, disconnect the circuit from the mains and check the radio components for heating.
When setting up and testing the device, the Safety Regulations must be observed.

PCB drawings in lay6 format (file The-push-pull-inverter.zip) you can download from our website: You do not have access to download files from our server

Vladimir Konovalov, Alexander Vanteev
Irkutsk-43, PO Box 380

Literature
1. Ilya Lipavsky. Hybrid power amplifier based on Andrea Ciuffoli repeater. - RadioHobby, No. 2, 2009, p. 49.
2. . - Solon-Press, Moscow, 2003, p. 108-142.
3. V. Konovalov. Methodological developments and articles. - Irkutsk, 2009.
Download: Push-Pull Inverter Based on Emitter Power Follower
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In push-pull converters, the magnetic core of the pulse transformer is used more efficiently. In such circuits, it is not necessary to deal with the magnetization of the core, which makes it possible to reduce its dimensions. The output voltage is symmetrical. In addition, the converter transistors operate in a lighter mode.

Sometimes, for low power (up to 15 W), the simplest converter is used, made according to the oscillator circuit (Fig. 4.16, a). This circuit is not critical to the parts used, but selecting the operating point of the transistor operation mode using resistor R2 can improve the performance of the device (sometimes a capacitor is installed in parallel with R2). The divider of resistors R1-R2 provides the necessary initial current to start the oscillator.

Rice. 4.16. Schemes of push-pull oscillators

The used universal transistors 2N3055 are replaced by similar domestic KT818GM, KT8150A, and if you change the polarity of the supplied power, you can also use p-n-p transistors. The supply voltage of the circuit can be from 12 to 24 V. For long-term operation of the device, transistors must be installed on radiators.

The transformer can be made on a ferrite M2000NM1 ring magnetic conductor, its working section depends. from the power in the load. For a simplified choice, you can use the recommendations, see table. 4.5.

Table 4.5. Permissible maximum power for ring ferrite magnetic circuits of the M2000NM1 brand

In the manufacture of transformer T1, windings 1 and 2 are wound at the same time, but the phasing of their connection must correspond to that shown in the diagram. For the section of the annular magnetic circuit of size K32x20x6, windings 1 and 2 each contain 8 turns (PEL wire with a diameter of 1.2 ... 0.81 mm); 3 and 4, 2 turns each (0.23 mm); 5 - the number of turns of the secondary winding depends on the required voltage (0.1 ... 0.23 mm).

Using this circuit, you can get voltages up to 30 kV if you use a magnetic circuit from transformers used in modern TVs.

A similar oscillator circuit, made on field-effect transistors, is shown in fig. 4.16b. It allows the use of a simpler transformer that does not require feedback windings. Zener diodes VD1, VD2 prevent dangerous voltages from appearing on the gates of transistors.

The operating frequency of such circuits is set by the parameters of the transformer magnetic circuit and the inductance of the windings, since the delay of the feedback signal depends on this (it is better if the frequency is in the range of 20 ... 50 kHz).

As a disadvantage of these circuits, one can note a low efficiency, which makes it difficult to use them at high power, as well as an unstabilized output voltage, which can vary greatly depending on the change in the supply voltage. A more successful push-pull converter circuit, made using a specialized microcircuit (Fig. 4.17), is highly efficient and can maintain a stable voltage at the load.

Rice. 4.17. Scheme of a push-pull pulse converter

The converter is made on the widely used T114EU4 PWM controller chip (a complete imported analogue of TL494), which makes the circuit quite simple. In the normal state (at zero gate voltage), transistors VT1, VT2 are closed and open with pulses from the corresponding outputs of the microcircuit. Resistors R7-R9 and R8-R10 limit the output current of the microcircuit, as well as the voltage at the gate of the keys. A chain of elements C1-R2 provides a smooth exit to the operating mode when the power is turned on (a gradual increase in the width of the pulses at the outputs of the microcircuit). Diode VD1 prevents damage to circuit elements when the power polarity is connected by mistake.

Voltage diagrams explaining the operation are shown in fig. 4.18. As can be seen in figure (a), the trailing edge of the pulse has a longer duration than the leading one. This is due to the presence of the gate capacitance of the field-effect transistor, the charge of which is absorbed through the resistor R9 (R10) at the time when the output transistor of the microcircuit is closed. This increases the closing time of the key. Since in the open state the voltage drops on the field-effect transistor is not more than 0.1 V, power losses in the form of a slight heating of VT1 and VT2 occur mainly due to the slow closing of the transistors (this is what limits the maximum allowable load power).

Rice. 4.18. Stress diagrams

The parameters of this circuit when working on a lamp with a power of 100 W are given in Table. 4.6. In idle, the current consumption is 0.11 A (9 V) and 0.07 A (15 V). The operating frequency of the converter is about 20 kHz.

Table 4.6. Main parameters of the scheme

The T1 transformer is made on two ring cores folded together made of M2000NM1 ferrite grade K32x20x6. The winding parameters are indicated in Table. 4.7.

Table 4.7. Parameters of the windings of the transformer T1

Before winding, the sharp edges of the core must be rounded off with a file or coarse sandpaper. In the manufacture of a transformer, the secondary winding is first wound. Winding is performed turn to turn, in one layer, followed by insulation with varnished cloth or fluoroplastic tape. Primary windings 1 and 2 are wound with two wires at the same time, as shown in fig. 4.19 (evenly distributing the turns on the magnetic circuit). Such winding makes it possible to significantly reduce voltage surges at the fronts when closing the field keys. Transistors are installed on a heat sink, which is used as a duralumin profile (Fig. 4.20).

Rice. 4.19 Design view of the pulse transformer

Rice. 4.20. Radiator design

Radiators are fixed on the edges of the printed circuit board. A single-sided printed circuit board made of fiberglass with a thickness of 1.5 ... 2 mm has dimensions of 110x90 mm (see Fig. 4.21 and 4.22).

Rice. 4.21. PCB topology

Rice. 4.22. Location of elements

This scheme can be used to power a load that constantly consumes power up to 100 watts. For more power, it is necessary to reduce the switching time of the field switches. This can be done by specially designed microcircuits that have a complementary output stage designed to control powerful field-effect transistors, for example, K1156EU2, UC3825.

As power switches for power up to 60 W in the above circuit, you can also use N-type transistors with static induction KP958A (BCIT- Bipolar Static Induction Transistor). They are designed specifically for operation in high-frequency power supplies. The physics of operation of such a transistor is close to that of a conventional bipolar one, but due to its design features, it has a number of advantages:

1) low voltage drop source-drain in the open state;
2) increased gain;
3) high switching speed;
4) increased resistance to thermal breakdown.

In this case, it is better to select transistors with the same parameters, and reduce the resistors R9 and R10 to 100 ... 150 Ohms.

Many radio amateurs for their practice tried to assemble a voltage inverter with their own hands. In this article I will talk about the design of an ultra-simple inverter, which is designed to receive 220 volt mains voltage from a car battery. The power of such an inverter is small, but this is one of the simplest options that can exist.

As indicated above, the circuit itself is made on just two powerful field keys. You can use literally any N-channel field-effect transistors with a current of 40 amperes or more. Cheap field devices of the IRFZ44 / 46/48 series are excellent, in order to increase the output power, you can use more powerful field-effect transistors of the IRF3205 series - the choice is huge, I have listed only the most common transistors that can be found in almost any radio parts store.

The transformer can be wound on a ring or armored core E50, the core is also not critical, as long as the windings fit. The primary winding is wound with two strands of wire 0.8 mm (each) and consists of 2x15 turns. When using armor cores with two sections on the frame, the primary is wound in one of the sections, as in my case. The secondary winding consists of 110-120 turns of copper wire with a diameter of 0.3-0.4 mm. It is not necessary to install interlayer insulation. An alternating voltage with a nominal value of 190-260 Volts is formed at the output of the transformer, but the shape of the output pulses is rectangular, instead of a mains sine.

The frequency of this deviates from the mains, so connecting active loads to the converter is quite risky, although practice shows that active loads with a switching power supply can also be connected to the output.

Practical application of push-pull inverter

The converter can easily power incandescent lamps, LDS, low-power soldering irons, etc., the power of which does not exceed 70 watts. Field keys are installed on heat sinks, in case of using a common heat sink, do not forget to use insulating gaskets.

The case is your fantasy, I took it from a Chinese 150-watt electronic transformer. The efficiency of this push-pull converter circuit can reach up to 70%. the author of the article is AKA KASYAN.

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On fig. 5 shows a diagram of a push-pull transistor amplification stage with a transformer input and output.

The upper arm of the amplifier forms a transistor VT 1 and upper half-windings of transformers TV 1 and TV 2, the lower arm includes a transistor VT 2, lower half windings of transformers TV 1 and TV 2. In the ideal case, both arms are exactly the same and the circuit is symmetrical about the horizontal axis passing through the midpoints of the transformers.

Amplifier can work both in class mode A , and the class IN . To transfer the cascade to the mode IN it is enough to reduce the bias voltage by R 2 (increase resistance R 1 and reduce R 2 , or exclude bias circuits) to a value that provides a cutoff angle of 90 0 . Consider class mode IN .

Circuit characteristic. Push-pull amplification stage with transformer input and output, series collector power supply, DC biased by resistor divider current R 1, R 2, assembled on n-p-n type transistors according to the OE scheme, operating in class mode IN .

Assignment of elements. Transformer TV 1 is designed to obtain two voltages of the same amplitude and opposite in phase, as well as matching the resistance of the signal source with the input impedance of the amplifier.

Transformer TV 2 ensures the matching of the load resistances with the output resistance of the collector circuits of the transistors.

Capacitor WITH bl1 blocks R 2 for AC, reducing the loss of the AC component of the input signal.

Divider R 1 , R 2 provides the required position of the HPT on the characteristics of the transistors.

The principle of operation of the circuit. When there is no input signal ( U 1 \u003d 0) and the power supply is on, the divider current flows. On a resistor R 2, a bias voltage is created, the value of which ensures the position of the NRT at the beginning of the pass-through static characteristics of the transistors. Both transistors are closed. No current flows through the TV2 transformer and the output voltage is zero. Thus, in static mode permanent currents through transistors do not leak those. in mode IN the quiescent current of transistors is almost zero, which already predetermines a reduced supply current consumption.

When an alternating voltage is applied to the input of the circuit, for example, a harmonic signal ( U 1 ¹ 0) on the secondary windings of the transformer TV1, two secondary voltages are formed, shifted relative to each other by 180 0 (see Fig. 5). As a result, one of the transistors, for example, the upper VT1, goes into active mode (opens) and the shape of the current through it repeats the shape of the applied voltage. The current pulse through the upper transformer flows through the circuit: + E k , upper half-winding TV2, K, KP, EP, E, ┴, - E k . It induces a current pulse through the secondary winding TV2, flowing through the load. And at the same time, the lower transistor is in cut-off mode and no current flows through the lower half-winding of the transformer.

When the polarity of the input voltage is reversed, the state of the transistors is reversed. In this case, the current pulse under the influence of the input signal flows in the lower arm of the cascade through the circuit: + E k , lower half winding TV2, K, KP, EP, E, ┴, - E k . As a result, a reverse current is excited in the secondary winding of the TV2 transformer.

Thus, a current flows through the load, the shape of which coincides with the shape of the control voltage ( U 1). Timing diagrams of the control voltage, currents through transistors, load and through the power supply are shown in fig. 6.

As follows from the figure, the current flowing through the transistors is a cosine pulse with a duration equal to half the period of the control voltage. Transistors here work strictly alternately : each passes a half-wave of current only in its half-period of oscillation (Fig. 6). In the second half of the period, it is locked and does not consume current from the power source. During this half-cycle, the second transistor operates. This mode is called class mode. IN . Collector currents of transistors VT1 and VT2 can be represented as a Fourier series:

Because the dots i k1 and i k2 flow around half of the TV2 windings in opposite directions, then the resulting magnetic flux created by them is proportional to their difference. The current through the load is proportional to the magnetic flux, therefore, for the current in the load, we can write

The current in the power supply circuit of the amplifier is equal to the sum of the currents of the arms:

From the results obtained it follows:

1. Since the output current contains only odd harmonics, in a push-pull cascade, compensation of even harmonics shoulder currents in load. This allows you to reduce the level of non-linear distortion using the economy mode. IN .

2. At the output of the cascade there will be compensate for all interference induced in-phase in the arms both from the power supply and from other sources. This reduces the sensitivity of the amplifier to supply voltage ripple, which makes it possible to simplify smoothing filters in power circuits.

3. Differential current of the shoulders does not contain a direct current component, while there is no permanent magnetization of the transformer core. This makes it possible to use this transformer at a higher output signal level or at a given output power to significantly reduce its dimensions, weight, and cost.

Since currents flow through transistors only in part of the period, and the rest of the time the transistor is closed, then the power dissipation of the transistor decreases, which allows using a transistor in a push-pull amplifier circuit that dissipates an order of magnitude less power than a transistor in a single-cycle cascade operating in class mode A with the same useful power. Calculations show that the efficiency in a push-pull cascade can approach 78.6%. This is achieved by a large utilization factor of the collector voltage and a small value of the constant component of the collector current (class mode IN ).

Form frequency characteristics power amplifier is determined by the frequency transformer properties. Analytical expressions for the frequency response coincide with similar expressions for a single-cycle transformer stage.

Disadvantages of the transformer stage:

large size, weight and cost;

Relatively narrow band of operating frequencies;

Distortions and large phase shifts at the edges of the passband, which prevents the coverage of the final stage of deep OOS, since stability is violated;

· the presence of transformers makes it impossible for the integral design of the PA. There are additional losses of useful energy in transformers, their efficiency is usually 0.7 ¸ 0.9.

In addition, the mode IN although it provides high efficiency, it introduces increased nonlinear distortion due to the curvature of the initial section of the transfer characteristic of transistors I To ( U be), as a result of which the combined characteristic of both transistors (Fig. 7, A), representing the dependence of their difference current, has a similarity of a step in the vicinity of the zero crossing.

This causes the so-called central steps on the residual current sinusoid (Fig. 7, b), and hence the output voltage.

To eliminate them, the AB mode is used, in which a small initial bias of the NRT A1 and A2 transistors is applied so that they are in the middle of the initial curved sections of the transfer characteristics (Fig. 8, A). Combining the voltage characteristics of transistors U be points A1 and A2, we see that the difference current characteristic turns out to be straight (dashed line in the figure) and no steps appear (Fig. 8, b). In the AB mode, at low currents, both arms operate simultaneously, similar to mode A, and the non-linearity of the characteristics of the arms is mutually compensated.

In AB mode, at low amplitudes, the efficiency of the final stage decreases (compared to mode B). However, the overall efficiency of the entire amplifier decreases little, since the quiescent current of the terminal transistors is usually less than the total supply current of the preliminary stages. The AB mode for push-pull stages is the most common, since it provides high efficiency and low non-linear distortion.

Two-stroke transformerless cascades

Transformerless circuits are increasingly used. With their implementation, it is easy to carry out a direct connection between the cascades (without coupling capacitors). They have good frequency and amplitude characteristics, they are easily performed using integrated technology, because do not contain bulky transformers. Most often, transformerless amplifiers are assembled according to a push-pull circuit and they operate mainly in AB mode.

The name "transformerless cascade" in the general case is conditional; the fact is that, as a rule, amplifiers use two or three element composite transistors in each arm. Therefore, the shoulder is a two-three-stage amplifier.

On fig. 9 shows one of the common diagrams of a two-stage transformerless power amplifier with parallel control of transistors of the final push-pull stage (on VT 2 and VT 3) single-phase alternating voltage.

To eliminate the need for two power supplies, load resistance R n connected via a decoupling capacitor C 2 to one of the source poles E n. This is possible because only alternating current flows through the load. Voltage between capacitor terminals C 2 almost constantly and close to E n /2. In AB mode, in a half-cycle when the transistor VT 3 opens, capacitor WITH 2 in the load circuit is connected in series with the source E n and their voltages are subtracted, so that the total supply voltage of one arm is equal to E P - E C2 = E n /2, and the capacitor WITH 2 partially charged by transistor current VT 3. In the half-cycle of the transistor VT 2 voltage capacitor E C2= E n / 2 serves as a power source and is partially discharged.

In high-power transformerless cascade circuits, it becomes difficult to choose a complementary pair of high-power transistors with the same or similar parameters. The output is the use of composite transistors in the arms of a two-stage output stage circuit.