12_V_CHARGER

Published:2009/6/29 22:45:00 Author:May | From:SeekIC

Heath GP-21 charger uses SCR as switch to connect and disconnect battery at 120-Hz rate. Voltage at anode of SCR D7 goes positive each half-cycle, putting forward bias on base of Q1 through 1.8K resistor so Q1 passes current through D5 to gate of D7 to turn it on for part of half-cycle and charge battery. D7 stays on until voltage across it drops to zero. When battery has eharged to 13.4 V, charging stops automatically. Rest of circuit protects against battery polarity reversal and accidental shorting of output leads. Special 12.8-V zener can be replaced by selected 1N4742 and forward-biased 1N4002.-H. Olson, We Don't Charge Nothin' but Batteriesl, CQ, Feb. 1976, p 25-28 and 69.



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