SU1737681A1 - Transistor voltage converter - Google Patents

Abstract

The invention relates to a converter technique, in particular to converters of direct voltage to alternating voltage. The purpose of the invention is to increase reliability by protecting the transistors of the converter against short circuits. A resistor 11, an RC circuit 13, 14, current limiting resistors 15, control transistors 16, 17, an additional power supply 18, locking resistors are inserted into the converter containing the transistor bridge with transistors 1 ... 4, the transformer 9 with the control current windings. 20. A start winding is inserted in transformer 9. The circuit makes it possible to increase the reliability of the converter in operation by protecting its T ranzistors from all types of short circuits due to the rational arrangement of the current and starting windings of the transformer, as well as by choosing the values of current-limiting resistors 2 or less. (Ls

Description

The invention relates to a converter technique, in particular to converters of direct voltage to alternating voltage.

Known switching circuits with overload protection inductive-capacitive load. In order to implement protective functions, a switching device containing switching transistors connected via a bridge circuit includes a load in one of the bridge diagonals and a power source in the other. This device also contains two auxiliary power supplies and additional resistors through which the load current flows. The voltage taken from them at the moment when the permissible load current is exceeded closes the additional current protection transistors.

Also known are transistor voltage converter circuits containing a power transistor bridge, a master oscillator based on a transistor bridge, where all transistors of both bridges are controlled through the control windings of the transformer connected between the base and the emitter of the transistor through a transformer connection with the load current, passage through the current winding of the transformer. This circuit is simple; it allows operation at high supply voltages.

The disadvantage of this circuit is the lack of protection against overload currents during short circuits.

The aim of the invention is to improve the reliability of the converter in operation.

WITH

Xi

about

00

by protecting transistors against short circuits.

The proposed scheme makes it possible to increase the reliability of the converter operation by protecting the power transistors from all types of short circuits.

The essence of the invention lies in the methods of protection against two types of short circuits.

When inter-turn closures, when the rate of current increase in the load increases, the voltage drop on the inductances of the current windings increases, which leads to short-term locking of the transistors to which the emitters of the current coils are connected, and due to the positive feedback locks the transistors to which control windings, and the current through the load ceases.

In the presence of short circuits in the load on the ground, which is connected to the zero point, the current begins to flow from the power source through the place of the circuit, to shunt the current windings. Due to the presence of positive feedback, the current entering the transistors through the control windings is stopped and the transistors are again locked, thus protecting the transistors from short circuits.

FIG. 1 shows the electrical circuit of the voltage converter; in fig. 2-diagram of the operation of the voltage converter.

The transistor voltage converter contains a transistor bridge with transistors 1-4, with discharge diodes 5-8, a transformer 9 with control windings connected in opposite directions to the bases and emitters of the first pair of transistors 1.2 connected by collectors to the power supply 10. In parallel with the transistors of the first pair, resistors 11 are connected. A load 12 of inductive nature is connected to the bridge diagonal. A parallel circuit is connected in parallel to the load, consisting of the starting winding of the transformer 9, the capacitor 13 and the resistor 14.

The starting winding is connected differently to one of the control windings having a common point with it. The transformer current windings are connected between the emitters of the second pair of transistors 3, 4 and the zero point of the power sources 10 (18) with opposite polarity to the zero point, but unipolarly with the control windings connected to the transistors 1, 2 of the first pair in opposite arms of the bridge, Base the second pair of transistors are connected to current-limiting resistors 15, the second ends of which are connected to the collectors of control transistors

16, 17, the emitters of which are connected to an additional power source 18, and the bases to the control circuit 19. The locking resistors 20 are connected between the bases of the transistors of the second pair 3, 4 and the zero point

0 schemes

The device operates as follows. When opening at time ti (Fig. 2) by the control circuit 19 of one of the transistors, for example, transistor 16, flows

5 base current ez (FIG. 2 a) to the zero point. The transistor 3 is unlocked and a current 114 (FIG. 2 g, g) starts flowing from the power source 10 through resistors 11, 14, capacitance 13, through the starting winding of the transformer 9,

0 transistor 3. The time and magnitude of this current is determined by the parameters of the elements 11, 14, 13, 9. Due to the presence of a transformer connection between the starting and control windings, transistor 2

5 opens the resistor 11 to the shunt, and a current 112 (Fig. 2h) begins to flow through the load 12, opening the transistors 2, 3 and the current winding of the transformer 9, the polarity of the voltage on the transformer windings

0 of this mode is indicated in FIG. one.

The current through the load 12, having an inductive nature, begins to increase due to the positive feedback between the current winding connected to

5 to the transistor 3, and the control winding of the transistor 2, the latter remains in the open state due to an increase in current 1b2 (Fig. 2g). In normal modes, the control circuit opens the transistor 2 for a time less than

0 is the time when the current through the inductive load 12 reaches the value at which the positive feedback is maintained (beats Fig. 2h) due to the short leading edge of the current Id passing through the current

5 winding.

When locked in time t2 (Fig. 2) by the control circuit 19 of the transistor 16, the transistor 3 also closes through its own closing resistor 20. self-induction EMF

0 of the transformer 9 reverses the polarity and sharp locking of the transistor 2 occurs, but the blocking voltage at its base – emitter junction does not reach dangerous values due to the base – emitter junction of the transistor 1, through which current 1b1 flows (Fig , 2 m) in the forward direction, opening it, but the current does not pass through it, since the load current flows from the load through the 5 Is diode (Fig. 2n), the power source and

the current winding of the transformer 9 and the diode 8 (Is Fig. 2 l), gradually reducing its value. In this case, the self-induced EMF of the current winding connected to the diode 8 is induced with the opposite sign (relative to the symbols in Fig. 1), in the direction blocked by transistor 2. When opened at time t2 of transistor 17, the circuit operates similarly up to time ts (Fig. 2), but the current through the load changes its direction.

In the event of a short circuit during XKz (Fig. 2), when transistors 2, 3 are open, at point 21, transistor 2 does not fail because the current through the current winding stops and the capacitance 13 is discharged by current 1 through the short circuit, the zero point, the diode 7 and the starting winding of the transformer, and a pulse is formed, the locking polarity for the transistor 2. If a short circuit point occurs at the other end of the load, then the transistor 2 is also locked due to the current flowing through the current weave connected to the transistor 3.

Another type of short circuit is interturn, due to which the inductance of the load decreases and consequently there is a rapid increase in the current through it.

To protect against inter-turn short-circuits, the voltage of the power source 18 and the value of the current-limiting resistors 15 are chosen so that at normal values of the current and its rise rate, when the base current of the transistors 3, 4 decreases, the voltage of the transformer does not lead to the output voltage 4 of saturation.

In the case of an increase in the rate of change of current through the load due to short circuits, the voltage across the emitter of transistor 3 (4) increases. It begins to go out of saturation, limiting the increase in current through the load and, if the current stops rising, the positive feedback between the current and control windings of the transformer is cut, the self-induced EMF changes its sign, which causes the transistor 2 (1) to lock. In this case

the failure of transistor 3 (4) does not occur, since the locking can occur at low currents through it and at a high rate of change of these currents. AND

active mode at low currents for the transistor is not dangerous. Further, if ZH abruptly becomes equal to zero, the entire voltage will be applied to the current winding and transistor 3 (4) will be momentarily locked and transistor 2 (1) will also close due to positive feedback, and the latter will remain in the locked state since the triggering winding will not be able to form a control pulse for it, being short-circuited through ZH.

Claims (1)

Claims of the Transistor Voltage Converter Containing a Transistor a bridge connected to the input terminals, and an output to a load circuit; a transformer having current windings, the control windings of which are connected to the control transitions of the bridge's upper transistors, characterized in that, in order to increase reliability by protecting transistors against short circuits, it has an RC circuit, two resistors, two control transistors, two current-limiting and two locking resistors, and an additional power source, and a start winding is inserted in the transformer, with the start winding and RC l connected in series and connected in parallel with the load circuit, the current windings of the transformer are connected in series with the emitters of the lower transistors of the converter, uniformly connected to the control windings connected to the upper transistors of the common-mode arms, the locking resistors are connected respectively between the bases of the lower transistors and the common point of the current windings of the transformer, the bases of the lower ones The transistors are connected through the corresponding current-limiting resistors and control transistors to the terminals of the additional power source, and the resistors introduced are parallel to the power transitions of the respective upper bridge transistors. Uli / l ™  P// -# I dt g „/ g you  Zi 0 D sixteen 18 p ol /} ya} 12. m nineteen SRG1 Dff Normal / PaSoma mode after short