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Build a Switching Power Supply Circuit Diagram. This is a Switching Power Supply Circuit Diagram. This low-voltage high-current output, switching de power supply is running off the 220-Vac input. In this schema, an ST2 diac relaxation oscillator, Q3, Cl, and the diac, initiates conduction of the output switching transistor Ql, the on-time of which is maintained constant by a separate tiring computation network consisting of Q2, C2, SUS, and SCR 1. 

The output voltage, consequently, is dependent on the duty cycle. To compensate for unwanted variations of output voltage because of input voltage or load resistance fluctuations, an HllC wired as a linear-model unilateral PNP transistor in a stable differential amplifier configuration is connected into the galvanic ally isolated negative-feedback loop. 

 Switching Power Supply Circuit Diagram

The loop determines the duty cycle and hence the output voltage. Of further interest in this schema is the use of several low-current, high-voltage, 400V VvRM thyristors (Q2, Q3,) which are also used as pnp remote-base transistors. Short-schema protection is assured by coupling Ql collector-current feedback into the tum-off schemary via Rss·