Photoelectric isolation circuit between TTL circuit and relay circuit

Published:2011/4/20 8:44:00 Author:Nicole | Keyword: photoelectric isolation, TTL, relay | From:SeekIC

In this circuit, using a photoelectric coupler can reach 100GΩ isolation between TTL and relay circuit, it avoids relay noise and peak voltage influencing TTL circuit. When the TTL input singal is high, Q1 turns on, there is no current in LED, and there is no light incident on detecor, photoelectric diode is in 5GΩ maximum impedance value. So Q2 is nonconductive, then Q3 is nonconductive too, and there is no current in relay coil.



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