Simple delay timing circuit

This article introduces a simple and practical delay timing circuit, which is especially suitable for lighting in stairwells and walkways where "someone turns it on but no one turns it off" or requires "people walking to turn off the light". It is very convenient to use. The circuit is shown below. During operation, after pressing S1 and S2, the rectified power supply charges C2, and the voltage at both ends of C2 quickly reaches the power supply voltage value. At the same time, the power supply provides base bias current to the composite tube composed of V1 and V2 through R, causing the composite tube to conduct, and the relay K is closed. Its contact K1-1 is closed together with S1 to provide AC power to the electrical appliance RL. S1 and S2 are loosened. RL can still work normally when it is on; but after S1 and S2 are loosened, capacitor C2 is discharged through R and the composite tube, keeping the composite tube in a conductive state to maintain the normal operation of RL; with the delay of time, the voltage on C2 If it is not enough to maintain the conduction of the composite tube, K will be released, and the power supply on the electrical appliance RL will be automatically cut off, thereby achieving the purpose of automatic shutdown. The length of the delay time is determined by the time constants of C2 and R. Changing the value of C2 or R can change the length of the delay time (the delay time is about 7 minutes according to the value in the figure). Increase the value of C2 or R, and the delay time will increase. becomes longer, otherwise the time becomes shorter. This circuit is simple to make and has no special requirements for components. After the installation is correct and the time constant of the RC is debugged, it can work normally.