Transformerless voltage converter. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters
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Transformerless voltage converter, the circuit of which is shown in fig. 4.12, consists of three parts: a master multivibrator on transistors VT3, VT4, two amplifiers on transistors VT1, VT2, VT5, VT6 and a rectifier on diodes VD1 ... VD4.
Consider the operation of the converter. Suppose that at the moment the transistor VT3 is open. The voltage on its collector decreases sharply from 6 V to 0. This voltage pulse will open the transistor VT2 and close VT1. The pulse at the output of transistor VT2 has the same voltage and phase as the input, but will be significantly amplified in current. From the emitter of the transistor VT2, it enters through the capacitor C1 to the rectifier. At the next moment, the transistor VT5 closes, and VT4 opens, and a process similar to that described occurs.
Since the left and right vertices of the rectifier bridge (see diagram) receive pulses of opposite polarity, the rectified voltage will be twice the supply voltage, i.e. 12 V. Due to the fact that the power transmitted from the primary circuit to the secondary is proportional to the frequency, the operating frequency must be sufficiently high.
Transistors VT3 and VT4 must have the same parameters. When using parts with the ratings indicated on the circuit diagram, the converter provided a voltage of 12 V in idle mode, 11 V at a load resistance of 100 ohms, 10 V at 50 ohms, 7 V at 10 ohms. Transistors BC107 can be replaced by KT315, AD161, AD162 - with GT402, GT404. Diodes D226 can be used in the rectifier.
Author: Semyan A.P.
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