SCR_PREREGULATOR_FITS_ANY_POWER_SUPPLY

Published:2009/7/5 21:20:00 Author:May | From:SeekIC

Circuit Notes This SCR pre-regulator keeps the filter capacitor Vc, in a variable output power supply, a few volts above the output voltage Vo. The benefits include: less heat dissipated by the pass transistor and therefore small heatsink, cooler operation and higher efficiency, especially at low output voltages.Q1, R1, R2, D1 and D2 form a constant current source for zener Z1, so that the contribution to the output current is always a few mA (2-3 mA).The Darlington pair Q2, Q3 keeps the SCR off. The voltage Vcdecreases until Vc= Vo=V at which point the Darlington pair fires the SCR, charging the filter capacitor to a higher voltage Vc1 in less than half the period of the input voltage. The component values, shown are for a 0-250-V, 3-A power supply.



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