SU1094119A1 - Push-pull self-exciting voltage converter - Google Patents

Abstract

DOUBLE-TERM SELF-EXCESSING VOLTAGE CONVERTER, those that contain a half-bridge cell on power transistors, and KtoezhK bases are connected to the first extreme terminals of the windings of the positive feedback of the output transformer, shunt frequency, and the same ones, which are set by one and one. wherein the capacitor of each RC circuit is connected to the input of the corresponding com- mument element, characterized in that, in order to increase the frequency stability, Each switching element is designed as a two-transistor analogue of a unijunction transistor, the output of which is connected to the i corresponding midpoint of the newly introduced voltage dividers on the CO resistors connected through additional diodes to the bases of the power transistors and to the second extreme ends of the windings of the positive feedback.

Description

with

The invention relates to converter equipment and can be used in the development of a secondary power supply source. Circuits of self-excited converters are known, in which either the switching core 1 or the switching transformer 2 is used as the mutator of the element that determines the frequency of the converter. The disadvantages of these circuits include the dependence of the conversion frequency on the magnitude of the input voltage. In addition, the presence of a switching throttle or transformer complicates these devices. Also known is a self-exciting inverter containing a transistor analogue of a single junction transistor 3 as a switching element. However, in this scheme, passive locking of power transistors is used, which, as compared with the active locking scheme, leads to a greater asymmetry of the converter shoulders, caused by the technological spread of transistors in the resorption time of minority carriers. The closest in technical essence is a converter containing a half-brimmed cell on power transistors, the bases of which are connected to the corresponding extreme terminals of the windings of the positive feedback of the output transformer shunted by the frequency reference RC circuits, and their emitters to the taps from these windings, The capacitors of the KS circuit are connected to the input of the switching elements on the transistors, the outputs of which, the collector, are connected to the bases of the power transistors. The switching frequency of the transform bodies is determined by the parameters of the RC circuit PI. In this converter, the functions of the master oscillator and power amplifier are combined in one device 4. However, the converter does not succeed in obtaining high stability of the frequency of the converter when the input voltage of the converter is varied. The purpose of the invention is to increase the stability of the conversion frequency. The goal is achieved by the fact that in a converter containing a half-bridge cell on power transistors, the bases of which are connected via current-limiting resistors to the corresponding extreme terminals of the positive feedback windings of the output transformer shunt by the partially-setting RC circuits, their emitters to the leads from these windings , with the capacitor of each KC-circuit connected to the input of the corresponding switching element, the latter made in the form of a two-transistor analogue of a single junction transistor, the output of which is connected to the corresponding midpoint of the newly introduced voltage dividers on the resistors connected through additional diodes to the bases of the power transistors and the second extreme leads of the positive feedback windings. The drawing shows a schematic diagram of the converter. The converter contains a half-bridge cell on capacitors 1, 2 and power transistors 3, 4, the bases of which are connected through current-limiting resistors 5 and b to the extreme terminals of the positive feedback windings 7 and 8 of the output transformer 9, shunted by a frequency-setting KS circuit MI of resistors 10 and 11 and capacitors 12 and 13, and the emitters are connected to the taps from these windings, and the capacitors of the KS circuit are connected to the input of the switching elements made on the basis of two-transistor 14. 15 and 16, 17 are analogous to a single junction transistor, the output of which is connected to the midpoint of voltage dividers on resistors 18, 19 and 20, 21 connected through additional diodes 22 and 23 to the bases of the power transistors and the second extreme windings of the positive feedback. The base-emitter junctions of the power transistors are shunted by reverse diodes 24 and 25. Rectifier 26 with filter 27 is connected to the output winding of the transformer. The converter operates as follows. Suppose that a positive polarity voltage is applied to the winding 8. Then transistor 4 is opened by TQcom, flowing through its emitter junction from winding 8 through resistor 6., Transistor 3 is locked by the direct voltage of diode 25 caused by current flowing through it from winding 7, through resistor 5. Primary winding through open transistor 4 is connected to to the capacitor 2, the voltage of the transformer core is reversal. The transistors 16 17 of the key amplifier are locked by a brother voltage applied to the emitter-base of the transistor 17, and do not affect the converter's behavior. Since the resistance of the resistor 21 is much greater than the resistances of the resistors 6 and 20, the current flowing through this resistor under the action of the voltage of the winding 8 is small and also does not affect the operating mode of transistor 4, Thus, the voltage at the base of transistor 17 is determined The trigger threshold of the key amplifier is equal to the voltage acting on the base of the transistor. The capacitor 13 is charged by the current flowing through the resistor 11 under the action of the winding voltage. As soon as this voltage exceeds the threshold, the transistors 16 and 17 open like an avalanche. The reverse voltage is applied to the base-emitter junction of transistor 4 and the current flowing from the winding 8 through the base-emitter junction of transistor 4, diode 23 and transistor 16, transistor 4 is closed. The magnitude of the closing current is determined by a resistor 20, the resistance of which is taken 5-10 times less than the resistance of resistor 6, and the voltage across the winding P, which is 1.5-2 times less than the voltage on the positive feedback winding. The polarity of the voltage on the transformer windings changes. The transistor 3 / is connected to the primary winding of the capacitor 1. Under the influence of the reverse voltage, the capacitor 13 is recharged, the transistors 16 and 17 are closed. Diode 23 prevents recharging of the capacitor 13 through the base emulator: a stern junction of transistor 17, thereby preventing the transistor 4 from opening again. In the following, the processes in the converter occur as in the case of an open transistor 4.

The charge time of capacitors 12 n 13 should always be less than the time of magnetization reversal of the transformer 9.

The balancing of the converter shoulders is carried out by resistor 10.

When a capacitor is charged, the voltage across it changes exponentially.

l 1

 Ut (8 Ui2Hl-e) - U, .j.

At a point in time equal to half-time generation, the voltage across the capacitor is compared to the threshold voltage of the key amplifier. Substituting these values into equation (2) we obtain the expression for the generation period

US + UIA

T 2RC 1n

 )

The amplitude of the voltage on the windings 7 and 8 should be 8-10 times greater than the maximum possible voltage of the emitter junction, 5 which is caused by the desire

to get rid of the effect on the operation of the technology converter of the transistors across this voltage, as well as the desire to achieve an increase in the stability of the conversion frequency.

The invention makes it possible to significantly increase the frequency of the converter. So, when the input voltage changes to + 15% deviation

the frequency of conversion from the initial value does not exceed 3.5%.

Claims (1)

A TWO-WAY SELF-EXCITING VOLTAGE CONVERTER containing a half-bridge cell with power transistors, the bases of which are connected via current-limiting resistors to the corresponding first extreme terminals of the positive feedback windings of the output transformer, shunted by frequency-specifying RC circuits, and their emitters from each RC circuit is connected to the input of the corresponding switching element, characterized in that, in order to increase the stability of the conversion frequency , each switching element is made in the form of a two-transistor analog of a single-junction transistor, the output of which is connected to the corresponding midpoint of the newly introduced voltage dividers on the resistors connected through additional diodes to the bases of power transistors and to the second extreme terminals of the positive feedback windings. to>