Relay control circuit

Published:2011/3/29 3:47:00 Author:Jessie | Keyword: Relay | From:SeekIC

220V power provide bias for Q3, Q4 at positive and negative half cycle by load RL, R1, D1 ~ D4, ZD1; Meanwhile it provides power for photoelectric coupler by R3, D5 ~ D8. When TTL circuit outputs signal of high level, photoelectric coupler connected in positive half cycle, so produces voltage drop in R5 ends, trigger SCR connected, load RL works. The whole circuit's functionis likea relay, but won't produce reverse induced voltage, and avoid load being damaged by high back voltage.



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