SU1539925A1 - Dc voltage converter - Google Patents

Abstract

The invention relates to electrical engineering and can be used in power supply systems. The purpose of the invention is to increase reliability by providing a smooth start. The converter contains power transistors 1.2 and output transformer 3. Output secondary rectifier 6 and capacitive smoothing filter 7 are connected to secondary winding 5. Basic windings 8.9 of output transformer 3 through third diodes 10.11 are connected to base-emitter junction of power transistors 1 , 2. The primary winding 12 of the current transformer 13 is connected in series with the primary winding 4 of the output transformer 3. The secondary windings 14, 15 of the transformer 13 are connected via resistors 16, 17 to the base-emitter junction of power transistors 1.2. In the device, during the start-up, the power transistors 1.2 open with short pulses, and in steady state, the current-proportional control of the transistors 1.2 is implemented, and their switching occurs along a safe path. 4 il.

Description

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1, 2 and output transformer 3. Output rectifier 6 and capacitive smoothing filter 7 are connected to secondary winding 5. Base windings 8.9 of output transformer 3 are connected via third diodes 10, 11 to base-emitter junctions of power transistors 1 and 2. The primary winding 12 of the current transformer 13 is connected in series with the primary winding 4 of the output transformer 3.

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The secondary windings 14 and 15 of the current transformer 13 through the resistors 16, 17 are connected to the base-emitter junctions of the power transistors 1 and 2. In the device, during the start, the power transistors 1 and 2 are opened by short pulses, 2 and switching them on a safe trajectory. 4 il.

The invention relates to electrical engineering and can be used in secondary power supply systems.

The purpose of the invention is to increase reliability by providing a main start.

FIG. 1 and 2 show the power unit diagrams of the proposed converter, examples of execution; in fig. 3 is a control node diagram; in fig. 4 - timing diagrams, explanatory works} 7 of the converter (indexes with variable correspond to the elements of the circuit in Fig. 1-3)

The DC converter (Figs. 1 and 2) contains the power transistors 1 and 2 and the output transformer 3, the primary winding 4 of which is included in the power circuit of transistors 1 and 2. The output rectifier 6 and capacitive smoothing are connected to the secondary winding 5 of the output transformer filter 7.

The base windings 8 and 9 of the output transformer through diodes 10 and 11 are connected to the control inputs of the power transistors 1 and 2. The primary winding 12 of the current transformer 13 is connected in series with the primary winding 4 of the output transformer 3 and the secondary windings 14 and 15 are connected through equalizing resistors 16 and 17 to the base-emitter transitions of the power transistors 2 and 1, and the extreme terminals of the control winding, consisting of the half windings 18.1 and 18.2, to the collectors of the control transistors 19 and 20 (Fig. 3). The bases of transistors 19 and 20 through resistors 21 and 22 are connected to the outputs 23 and 24 of the driver 25 for control pulses. Additional winding 26 output trans

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of the formatter 3 through an additional rectifier 27 is connected to a serial circuit consisting of a resistor 28 and a capacitor 29, to the common point of which through the resistor 30 is connected the base of the transistor 31, which through a resistor 32 is connected to the output 33 of the control driver 25. The emitters of the transistors 19, 20 and 31 p - p - n - type are connected to the output 34 of the power supply, to the second terminal 35 of which the emitters of transistors 36 - 38 p - p - p are connected. In this case, the transistor 36 shunts the baso-emitter junction of the transistor 38, between the collector of which and the common point of the half-winding 18.1 and 18.2 of the current transformer 13 are connected in series with a resistor 39 and a diode 40. The collector of transistor 37 is connected to the base terminals of transistors 19 and 20. Vaz transistors 36 and 37 through resistors 43 and 44 are connected to the collector of transistor 31, and the base of transistor 38 through resistor 45 is connected to terminal 34. A diode 46 is connected between the common point of the half-winding 18.1 and 18.2 of the current transformer 13 and terminal 34.

The Converter operates as follows. I

Shaper 25 control pulses generates a sequence of unipolar pulses, with the pulses at outputs 23 and 24 being shifted by 180 degrees el., And the frequency of pulses at output 33 is twice as high as the frequency of pulses at outputs 23 and 24. In the initial state up to time point t0 (fig. 4), power transistors 1 and 2 are closed, capacitors 7 and 29 are discharged.

At time t0, a pulse from the output 23 of the driver 25 of the control pulses opens the transistor 19. The signal from the output 33 holds the transistor 31 in the closed state. The closed state of transistor 31 corresponds to the open state of transistor 38, and the current from the power source is closed along the circuit: pin 35 - collector-emitter junction of transistor 38 - resistor 39 - half-winding 18.1 of current transformer 13 junction collector-emitter of transistor 19 - pin 34. Current flowing through the half winding 18.1, is transformed into the secondary winding 14 of the current transformer 13. The power transistor 1 is opened and maintained positively by positive feedback between the windings 14 and 12. The voltage drop at the base-emitter junction of transistor 1 and resistor 16 is applied to the winding 14 of the current transformer 13 and transformed into the winding 18, with the result that the current through transistor 1 decreases or stops (if the voltage at the half winding 18.1 is greater than or equal to the voltage between the terminals 35 and 34).

In the time interval t., The input voltage through the open transistor 1 is applied to the primary winding of the output transformer 3 (polarity without brackets) and the capacitor 7 of the output filter is charged. At the same time, the voltage of the winding 26 through the rectifier 27 and the resistor 28 causes the capacitor 29 to charge. I

At time t, transistor 31 opens. The open state of transistor 31 corresponds to the open state of transistor 37 and the closed state of transistor 38. As a result of opening transistor 37, current flows through resistors 41 and 42 and the base-emitter transitions of transistors 19 and 20, causing the latter to open. As both transistors 19 and 20 open, the winding 18 of the current transformer 13 is shorted and in the time interval C-ta the power transistor 1 closes. Absorption current of minority carriers from the base of the power transistor 1

1539925

is transformed into a half-winding 18.2 and is closed through diode 46 and transistor 20. There is no current through resistor 39 and diode 40, because transistor 38 is closed.

At time tj, the transistor 31 is closed, the transistor 20 remains in a saturated state, and the transistor 19 is closed. As a result, the power transistor 2 opens, and in the time interval the charge of the capacitors 7 and 29 continues. At the time t ". opens

5, the transistor 31, and in the time interval, the power transistor 2 is closed.

As a result of a sequential-alternating supply of the trigger pulses to the bases of the power transistors 1 and 2, the capacitor of the output smoothing filter 7 and the capacitor 29 are charged. After the next opening of the power transistor 2, the voltage on the capacitor 29 at time t6 exceeds the threshold value (shown in FIG 4), which is characterized by the fact that in further operation the transistor 31 is not opened by the pulses of the driver 25 of the control pulses, but remains the closed voltage of the capacitor 29. Therefore, oic transistor 2 remains open until the end of the half cycle.

Switching power transistors in steady state occurs as follows. At time tj, the transistor 20 opens. The power transistor 2 begins to close, and in the time interval tT-tg, the resorption current from the winding 1b is transformed into a half-winding 18.1 and is closed through the transistor 19 and the diode 46. The current of the series circuit formed by the open transistor 38, resistor 39 and diode 40, in the time interval, also flows through diode 46 and transistor 19, reducing the current in the diode and increasing in the transistor.

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At the moment in time te, the resorption process ends and the transistor 2 closes (the final duration of the current falling edge can be neglected). After the transistor 2 is closed, in the time interval tg-t.j, the voltage on the windings of the output transformer retains its sign (polarity in brackets) until it closes

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the rectifier diodes 6. In this time interval (t8-t), the power transistor 1 is held in a closed state by the voltage of the winding 8 of the output transformer 3, and the current of the winding 14 of the current transformer 13 is closed through a resistor 16, diode 10 and the winding 8 of the output transformer 3 .

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After the diodes of the rectifier 6 are closed, at the time tg the magnetizing current of the output transformer 6 closes through the primary winding and iodine shunting the power transistor, the voltage on the windings of the output transformer 3 changes its sign (polarity without brackets), the diode 10 closes and the current of the winding 14 of the current transformer 13 is closed through the base-emitter junction of the power transistor 1. Transistor 1 opens and due to the positive feedback between the windings 12 and 14 of the current transformer 13 is held in its saturated state.

Thus, in the steady-state mode, the power transistors are switched along a safe path.

At time t (0, the transistors 19 and 20 are switched, while the processes in the device proceed in the same way as described.

In the event of a short circuit at the output of the converter or the connection of a capacitive load, the voltage on the capacitor 7 decreases, the capacitor 29 discharges. As a result, transistor 31 opens and the open time of power transistors 1 and 2 decreases.

Due to the short duration of the opening pulses (up to 1-2 X), the current through the power transistors 1 and 2 does not exceed the maximum permissible value even during a short circuit at the output of the converter. When a short circuit is removed (or the charging process of the connected capacitor is terminated), the converter enters the established mode and the transistor 31 closes.

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In the proposed DC / DC converter, there are no overloads of the power transistors during start-up when connected to the secondary winding of the output transformer0

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torus straightener with capacitive smoothing filter. Steady-state power transistors are switched along a safe path. This makes it possible to increase the reliability of the device.

Claims (1)

Invention Formula A DC converter containing a push-pull inverter with an output transformer, to the secondary winding of which is connected an output rectifier with a capacitive smoothing filter, a current transformer whose primary winding is connected in series with the primary winding of the output transformer, the secondary windings are connected to the control inputs of power transistors, and the extreme leads of the control winding are connected to the collectors of the first and second control transistors of the same conductivity type, whose emitters They are connected to the first input terminal of the converter, and bachy - to the outputs of the driver for control pulses, the third control transistor of opposite conductivity type, an emitter connected to the second input terminal of the converter, and a collector through the serially connected first resistor and diode to the midpoint of the control winding current transformer, the fourth control transistor, the emitter of which is connected to the first input terminal of the converter, and the base is connected via the second resistor to the output} control pulse, the second diode, one output of which is connected to the midpoint of the control winding of the current transformer, has been added so that, in order to increase reliability by ensuring a smooth start, a fifth and the sixth control transistor, an additional rectifier, a capacitor, the third, fourth, fifth and sixth resistors, and the output transformer is equipped with base and additional windings, while the base windings are connected through third diodes in parallel with base-emitter power transistors The additional winding is connected via an additional rectifier to a series circuit consisting of a third resistor and a capacitor, in parallel with which the base-emitter junction of the fourth control transistor, the collector of which is connected to the base of the fifth control transistor, whose output terminals shunt is connected via a fourth resistor base-emitter junction of the third control transistor, and to the base of the sixth. ttglg tg fi ".3 the control transistor whose emitter is connected to the second input terminal of the converter, and the collector is connected via the fifth and sixth resistors to the bases of the first and second control transistors, respectively, and the second terminal of the second diode is connected to the first input terminal of the converter. fig.g Schi g L