SU1467700A1 - Non-variable d.c. voltage converter - Google Patents

Abstract

The invention relates to converter equipment and may be used to protect unregulated self-oscillating converters during short circuits in the load. The purpose of the invention is to increase the reliability of the converter. In an auto-oscillator with proportional current control during a short circuit in the load using transistors 18 and 19, the additional winding 17 of the current transformer 7 is short-circuited, which leads to locking of the power transistors 2,3. A base-to-emitter junction of transistors 18.19 is connected in series with the zener diode 22, the resistor 14 and the diode 20 between the positive power supply bus and the positive terminals of the 21 rectifiers. 1 il. S (l

Description

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-bt The invention relates to converter equipment and may be used. It is used to protect unregulated self-oscillating converters during short circuits in the load.

The aim of the invention is to increase the reliability of the converter.

The drawing is a schematic diagram of an unregulated DC / DC converter.

An unregulated DC converter contains a power supply 1 with positive and negative buses, a push-pull self-oscillating inverter on power transistors 2 and 3, the emitters of which are combined with a power transformer 4 and a diode 5 and 6 of the rectifier, a current transformer 7 with two primary windings 8 and 9, each of which is connected in series to the collector circuit of each of the transistors 2 and 3 of the inverter, with a secondary winding 10, the beginning and end of which are connected to the bases of transistors 2 and 3, respectively, tap 1 1 from the midpoint of the winding 10 is connected to the cathode of diode 12, the anode of which is connected to the common emitter point of transistors 2 and 3, and a capacitor 13 connected to said diode in parallel — a trigger circuit containing a first resistor 14 and a second resistor 15 biased by a capacitor 16 , an additional winding 17 of a current transformer 7, two transistors 18 and 19, connected by emitters and bases, the collector of one of which is connected to the beginning, and the collector of the other with the ends of the additional winding 17, diode 20, an anode connected to a common point in, and a cathode to the positive terminal 21, a zener diode 22, the anode of which is connected to the point of combining without additional input transistors 18 and 19, and the cathode to the junction of resistors 14 and 15 run the converter circuit,

An unregulated constant voltage converter operates as follows.

When the supply voltage of the power source 1 is applied, the current flows through the starting circuit and the base-zmitter transitions of transistors 2 and 3. When the transistor is unlocked, for example, 2, a positive current feedback occurs, resulting in the full unlocking of transistor 2, and the locking of transistor 3. After the current transformer 7 is locked, the polarity on the secondary winding 10 changes. There is an avalanche-like process of unlocking the transistor 3 and locking the transistor 2, thus there is a self-oscillatory mode. At the output terminals 21, a voltage appears, determined by the supply voltage of the source 1 and the transformation ratio of the transformer 4, the transistors 18 and 19 are locked. The voltage on the Zener diode 22 during the startup process increases exponentially, the time constant of which practically depends on the resistance of the resistor 14 and the capacitor 16 capacitance. At the same time, the voltage on the Zener diode 22 does not reach the breakdown voltage.

When overloaded or short-circuited in the load, the voltage on the Zener diode reaches the voltage of the circuit and the following :, positive supply source 1 bus, resistor 14, zener diode 22, base-emitter junction transistors 18 and 19, diode 20, output terminals 21, negative bus source 1 current flows, enabling the transistors 18 and 19,

With this, the additional winding 17 is short-circuited and the transistors 2 and 3 of the inverter are locked, providing protection for the converter. Due to the significant gain factor of the transistors 18 and 19 and the presence of the Zener diode 22, the protection circuit has an almost on-off characteristic. This allows you to exclude the operation of the transistors 2 and 3 of the inverter in the active mode, t, e. increases the reliability of the converter.

Claims (1)

Invention Formula An unregulated DC converter containing a push-pull self-oscillating inverter on power transistors, the emitters of which are connected to the negative power supply, a power transformer with a rectifier on the output, the negative terminal of which is connected to the negative power supply bus, a current transformer with two primary windings, included-, in series with the collectors of the power transistors, and the secondary winding with the middle point, the beginning and 146 the end of which is connected to the bases of these transistors, and the midpoint to the cathode of the first diode, the anode of which is connected to the negative power supply bus, a capacitor parallel to the first diode, a resistive-capacitive trigger circuit connected between the positive power supply bus and the midpoint of the secondary windings of the current transformer, and the second diode, the cathode connected to the positive output of the rectifier. 700 characterized by the fact that, in order to increase reliability, two transistors are integrated in the negch), united by bases and emitters, and a zener diode, and an additional winding is inserted into the current transformer, the bases of the transistors being connected to the midpoint of the starting circuit through the zener diodes, diode, and collectors - to the beginning and end of the additional winding of the current transformer.