Morning and evening light-operated switch circuit

Published:2011/11/23 21:07:00 Author:May | Keyword: light-operated switch, Morning and evening | From:SeekIC

This kind of switch acts when it is above or below a cetrtain illumination, andits typical application is morming and evening street light auto switch. Diagram (a) and (b) show two circuits which adopt cadmium iodide photoresistor RPY20 directly supplied by AC electric fence. 1KΩ resistor isused to reducecurrent pulse. Relay coil 's essential resistance is 21.8Ω, and the pull-in voltage is 45V, release voltage is 18V. The capacitor connected with it in parallel makes up the RC with time constant in 0.1s, in order to minish the pulse DC voltage output by short-lived light flash and smoothness diode and prevent relay tremble, the relay touch point in diagram (a) circuit is normal closed. During the day,theillumination intensity is strong ( >31~45lx), thephotoresistance resistance is small, relay acts, andtouch point isopen, lamp goes out. At night, when illumination intensity is weak (<8.5~11lx) , on the contrary, the relay touch point in diagram (b) is normally open, its work is opposite from diagram (a).



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