SCR_REPLACING_LATCHING_SWITCH

Published:2009/7/10 3:25:00 Author:May | From:SeekIC

This circuit provides the turn-on characteristics of an SCR, but turns off with ease. The switch is comprised of three transistors with descending current ratings: Q3 has a high-current rating and Q2 has a medium rating. The current, I1, to be switched is 15 A. Momentarily depressing S2 removes Q1's base drive, turning Q1 off and allowing Q2 to turn on. Q2 then drives the base-emitter junction of Q3, turning Q3 on. Q3's collector-emitter voltage, which serves as Q1's base drive, is essentially zero, keeping Q1 off. To turn Q3 off, depress S1; this action momentarily shunts Q2's base current to ground, reversing the chain of events that turned Q3 on.



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