SU907739A1 - Push-pull transistorized inverter - Google Patents

Description

one

The invention relates to constant voltage converters and is used in secondary power sources.

Two-stroke, self-excited, push-pull converters are known in which resistive and diode starting circuits are used.

In resistive starting circuits, the displacement of the operating point of the power transistors, necessary for self-excitation of the converter, is provided by the voltage drop across the base resistor. The initial base current of the power transistors is 20-30% of the current of the resistive divider 1.

The disadvantages of resistive start-up schemes include an increase in through currents of power transistors in a steady state at the moment of switching, due to the initial bias, as well as a significant power dissipated in resistors that shift the operating point of the transistors, which reduces the efficiency and reduces the efficiency of the converter.

The use of diode trigger circuits only reduces the power dissipated by the divider resistors, however, the self-excitation of the converter becomes rigid, which is significant at low temperatures.

A push-pull converter with a disconnecting starting circuit 2 is also known.

However, during operation, especially when switching loads and when the input voltage drops, an oscillation failure may occur, which leads to a drop in the output voltage by the recovery time of the trigger circuit, which is several times longer than the trigger circuit off time. For this reason, this startup scheme has not found wide application in 15 converters operating through a rectifier for active-capacitive load.

Claims (3)

The technical solution closest to the technical essence is a push-pull transistor inverter containing power switching transistors, whose collectors are connected to the output transformer, and through diodes to the base of the starting transistor, whose collector junction is ground by a resistor and connected to one of the input pins, and the emitter is connected with the windings of the feedback and the bases of the power transistors 3. The disadvantages of the known device are low reliability, the circuit due to the occurrence of large pulses tra.nzistorov s power at the time of switching, and low efficiency. C € l invention - increase reliability and increase efficiency. The goal is achieved by launching resistors and a capacitor connected to the junction of the starting transistor, the emitter of which is connected via the starting resistors to the bases of the power transistors, in a push-pull transistor inverter. The drawing shows a push-pull DC voltage converter containing a transformer 1, the power winding 2 of which is connected to the collectors of power transistors 3 and 4, the middle point of the power winding of the transformer is connected to the first (positive) input terminal, and the emitters of transistors 3 and 4 are connected with another input output, to the KOTORO.Mu connect iUJ middle point of the winding 5 of the exciter, the ends of which through the resistors 6 and 7 are connected to the base.m of the transistors 3 and 4, where the starting resistors 8 and 9 are also connected, the other end under Switches connected to the emitter of the starting transistor 10 to the output of the power winding of the transformer are connected to the negative terminals of diodes 1 and 12, which are connected to the base of the starting transistor 10, the collector of which is connected to the first (positive) input transistor of the starting transistor , the control junction of the starting transistor is connected to the RC circuit consisting of a resistor 13 and a capacitor 14. The converter operates as follows. 1 When the supply voltage is applied, the starting transistor 10 is opened, the load of which are resistors 6-9. The voltage drop across the resistors is 80% from the supply voltage, which provides the initial collector current of transistors 3 and 4 necessary for self-excitation of the converter. The amplitude of oscillations increases smoothly as the capacitance is charged at the crunch. At the same time, charge through diodes 11 and 12 of capacitor 14 occurs, the voltage on which corresponds to the amplitude of oscillations in the collectors of transistors 3 and 4. At the same time, the voltage drop across the starting transistor 10 increases, which leads to a decrease in the initial bias current through resistors 6- 9. In the steady state, the starting transistor is completely locked by the bias on the capacitor 14, which ensures the disconnection of the converter's starting circuit, and the switching process of YpansHCTOpoB 3 and 4 is provided with the dissipation inductance of the transformer 1. The time constant of the RC circuit is selected from the condition of switching of the converter and There is a value of the order of one period. When the oscillations break down, the capacitor 14 is discharged through the resistor 13, and after 1-2 periods the startup circuit is restored. Thus, the output voltage of the starting transistor, and consequently, the initial offset of the transistors 3 and 4, as it were, “follows the amplitude of the oscillations. The application of the proposed DC-DC converter circuit ensures a gentle self-excitation, with a minimum recovery time. In addition, the invention allows for both active and active capacitive loads to disconnect the start-up circuit smoothly as the amplitude of oscillations increases. The RC time constant is selected from the conditions of the ripple filtering at the moment the converter is switched on and the order of one period can be selected, i.e., significantly less than the constant load time of the converter, while generation failures and short-term input voltage drops do not result significant output voltage drops. Converter self-excitation is soft, i., E. at the initial stage is similar to resistive start. At the same time, the disconnection of the starting circuit in a steady state allows reducing the through (pulse) currents of the power transistors at the moment of switching, eliminating losses on the starting resistors, which ultimately leads to an increase reliably (ti and -efficiency of the converter). and determines the possibility of applying the circuit when working on an active-capacitive load. Formula of invention A push-pull transistor inverter containing power transistors, the collectors of which are connected to the output transformer, and through diodes to the starting base transistor, to a 1-junction junction of which is bounded by a resistor and connected to one of the input pins, and the emitter is connected to the feedback windings and power transistor bases, characterized in that, in order to increase reliability and efficiency, the starting resistors and a capacitor are inserted into it connected to the junction of the starting transistor, the emitter of which is connected through the starting resistors to the bases of the power transistors. Sources of information taken into account during the examination 1. V. Moin, N. N. Laptev. Stabilized transistor converters. M., “Energie, 1972, p. 448. 2.Veresov G.P., Smurkov iO. L. Stabilized power sources of radio equipment. M., “Energie, 1978, p. 144 3. USSR author's certificate number 628596, cl. H 02 M .7 / 537, 1977.