555_TRIGGER

Published:2009/7/14 22:49:00 Author:Jessie | From:SeekIC

Low-cost 555 timer provides ON/OFF and proportional-control switching of AC loads without generating RFI or voltage spikes. Timer is used in monostable mode, retriggering every half-cycle when voltage at pin 2 falls below about 1.67 V. R3 and C1 fix pulse width at about n ms, long enough to ensure firing SCR in next half-cycle yet short enough to turn SCR off at next zero-crossing without timing-cycle pulse. Pin 4 serves as ON/OFF control input. Varying duty cycle of square wave here gives proportional control for heating and other uses.-M, E, Anglin, Low Cost Zero-Cross Thyristor Trigger Uses a 555 IC, EDN Magazine, Sept. 5, 1977, p 180-181.



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