SU862340A1 - Two cycle transistorized inverter - Google Patents

Description

(54) TWO-TERM TRANSISTOR INVERTER

one

The invention relates to a converter technique and can be used in power supply systems for converting a constant voltage to an alternating or constant other level.

In the well-known two-stroke transistor inverters, made according to the scheme with an output transformer and switching transformer or choke, one-sided biasing of the output transformer core occurs, due to the unbalance of the inverter arms and load, when the single-sided biasing of the transformer, its core in one of the half-periods goes into deep saturation mode ( RGN), accompanied by an increase in the magnetizing current and a significant increase in the instantaneous power switched by the inverter 1 .

For automatic balancing of the inverter by the current of the power transistors, blocks of various kinds of sensors are introduced into its composition, which detect the bias of the transformer and correct the duration of the half-aryds to decrease the bias 2, 3.

Such balancing devices are essentially automatic control systems with feedback on the difference in magnetization currents in the positive and negative half-periods. The disadvantage of inverters with automatic balancing, in addition to great complexity, is the possibility of self-oscillations in the circuit of magnetizing current control with a sharp change in the load current and voltage. With these fluctuations, the transformer can go into the RGN, causing overload of the transformers, which reduces the reliability of the inverter.

Claims (4)

The closest in technical essence to the device is a push-pull transistor inverter containing a switching transformer, the secondary winding of which is connected between the bases of the transistors connected via diodes to the input terminal connected to the emitters of these same transistors. An additional balancing winding through the diodes and the resistor is connected to the tuning potentiometer. It adjusts the saturation time of the switching transformer in the positive and negative half-period, which allows the inverter to be balanced by the current of the power transistors 4. The device has the disadvantage of instability of the symmetric mode obtained once when the inverter is tuned. For example, when a load is connected asymmetrically over half cycles, or simply when the load current fluctuates, the voltage at the base-emitter junctions of the transistors varies in different ways. As a result, the voltage on the windings of the switching transformer will differ in different half-periods, which will lead to a change in the duration of the half-periods set when setting up and the appearance of the output transformer. As a result, an overload of the inverter power transistors occurs, which reduces its reliability. The aim of the invention is to increase the reliability of the inverter and simplify the device. The goal is achieved by the fact that in a two-stroke transistor inverter resistors are inserted into the emitter circuit of the transistors. The drawing depicts an inverter circuit. The inverter contains an output transformer 1; starting resistor 2; switching transformer 3, the secondary winding of which is connected between the bases of transistors 4 and 5 connected via diodes 6 and 7 to the power terminal, additional resistors 8 and 9. The device operates as follows. After supplying power, the inverter is driven through the starting resistor 2 and operates as a normal oscillator with transformer current feedback carried out by the switching transformer 3. The switching period of the inverter is equal to the over magnetising time of the switching transformer 3, which is inversely proportional to the voltage F, on its winding . This voltage is equal to the sum of the voltage drops at the base-emitter junction (Ujj), on the additional resistor (Up) and diode (Ug): Е + Jf + Ц Suppose that in even half-periods (transistor 4 is on) the output transformer 1 is saturated. At the end of these successive periods, due to the growth of the magnetizing current of transformer 1, the voltage U on the resistor 8 increases. As a result, E is ignited on the winding of the switching transformer in even-numbered periods and its accelerated magnetization increases. As a result of this, the magnetized half-periods are shortened and the peak of the magnetizing current is limited. In this case, the output transformer operates in the initial biasing mode with a small difference in current over half periods. In order for the magnetizing current limiting process to be sufficiently effective, the voltage drop U (on resistors 8 and 9 must be commensurate with the voltage E on the winding of the switching transformer. When the winding is turned on directly (without resistors) and when using silicon diodes and transistors, the voltage drops resistors 8 and 9 should be 1–1.5 V. The introduction of these resistors reduces the magnetizing current peaks by 4–3 times. The power losses from additional resistors do not exceed the power losses in transistors from pi magnetizing current, so that the efficiency of the inverter increases slightly. However, the main effect of the introduction of additional resistors is to reduce the instantaneous power loss generated in the transistor during a short shutdown interval. It is the overload of the transistors with the instantaneous power that is most often the cause of the accidents of transistor inverters. Therefore, a decrease in the current switched by the transistors in the “magnetized half-period increases the reliability of the inverter. The use of the device in secondary power sources allows increasing their reliability practically without complicating the design. A push-pull transistor inverter containing a switching transformer, one of the windings of which is connected between bases of transistors connected via diodes to one of the input terminals connected to emitters of the same transistors, in order to increase reliability and simplify the device , resistors are inserted into the emitter circuit of the transistors. Sources of information taken into account in the examination. Sat “Current tasks of converting technology. Kiev, 756, Part 4, p. 334 2. Authorship of the USSR N ° 551782, cl. H 02 M 7/537, 1977. 3. USSR author's certificate number 551781, cl. H 02 M 7/537. 1977. 4. USSR author's certificate M 529533, cl. H 02 M 7/537, 1976.