Timing trigger switch circuit

Working principle: As shown in the figure. The AC power supply is stepped down by capacitor c1, bridge rectified by diodes vDl-vD4, filtered by capacitor c2, and a 12V DC voltage is obtained at both ends of the zener diode VD5. After rectification and current limiting through diode vD6 and resistor R2, the power supply voltage charges capacitor c4 through potentiometer RP and resistors R3 and R4. When the voltage at both ends of c4 is charged to the time base integrated circuit and the ②⑥ pin of A is greater than 2/3 of the power supply voltage, A is in the reset state, its ③ pin is at low potential, and the relay KM is closed, causing the common movable contact to activate. To control triggered circuits or colored lights. At the same time, c4 begins to discharge to pin 1 through R4 through pin ⑦ of A. When the discharge reaches the point where pins ② and ⑥ of A are less than 1/3 of the power supply voltage, A is in the trigger position, and its ⑥③ pins change from low potential to The local potential, KM is released, and at this moment the power supply voltage begins to charge c4 again. Among them, R1 provides a leakage circuit for c1. Capacitor c3 is a filter component. vn8 is the protection diode. vD7 is an isolation diode used to stabilize the timing memory.

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