Automatic delay light switch circuit

Published:2011/4/26 3:54:00 Author:Nicole | Keyword: light switch | From:SeekIC

The working principle: the circuir is as shown. A, B are connected to the two terminals of switch. Closing switch S, the positive half cycle of AC will trigger SCR turn-on by D6、R2、R1、D1 and SCR control pole; the negative half cycle of AC by D4、R2、R1、D1 and SCR control pole will trigger SCR turn-on. After SCR turn-on, it is equal to short circuit C, D points, so A, B pointsare closed by diode and the turn-on SCR. The light is on. After switch S off, the SCR still has trigger current and keep conductive, due to the capacitor C1 is discharging to it by R1, D1 and SCR control pole. The current is decreasing, after a few minutes, SCR off, then light goes out. The delay time is about 40~50s. The component selection: to choose SCR with 1A maximum current, 400V voltage. 1N4004 can be used for D1、D3～D6. C1 adopts 630V, 35μF color capacitor. After closing switch S, the light is not on, you can decrease the resistance of R1 properly.



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