Automatic delay lighting switch circuit

When leaving a room at night, always turn off the lights first. But if the light switch is not at the door, it is very inconvenient to turn off the light and then walk to the door in the dark. The switch introduced in this article uses only 9 components and can be easily added to the original switch to delay your lights for tens of seconds after being turned off, giving you enough time to leave the room and avoid being caught in the dark. bitter. Working principle: The circuit principle is shown in the figure below. A and B are connected to both ends of the original switch respectively. When the switch S is closed, the positive half cycle of the alternating current passes through D6, R2, R1, D1 and the thyristor control electrode, triggering the thyristor to conduct; the negative half cycle of the alternating current passes through D4, R2, R1, D1 and the thyristor control electrode. , triggering the thyristor to conduct. After the thyristor is turned on, it is equivalent to short-circuiting points C and D, so points A and B are also closed through the diode and the turned-on thyristor. At this time the light is on. After the switch S is turned off, because the capacitor C1 is discharged through R1, D1 and the thyristor control electrode, the thyristor still has a trigger current to maintain conduction. The discharge current gradually decreases. After a period of time, the thyristor is cut off and the light goes out. The delay time of this circuit is about 40 to 50 seconds. Component selection: Choose a thyristor with a maximum current of 1A and a withstand voltage of 400V. D1, D3~D6 can use 1N4004. C1 uses a color TV capacitor with a voltage of 630V and 35μF. If the S light does not light up when the switch is turned on, the resistance of R1 can be appropriately reduced.