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Delay timer circuit for switch ON

Delay ON Timer circuit using transistor

Delay Timer For Switch ON Supply To Any Appliance For Protection

Delay timer is a device which is used to take some duration before switch on the main input supply to any equipment . This is a protection circuit to protect any electrical or electronic equipment and appliance from sudden high or unstable voltage. 

Delay timer take on hold the supply some moment and then starts to flow. This is done by using the Relay in Delay timer circuit. Here i present a very easy and simple circuit of ON Time delay timer circuit which is made using 2 transistors, some resistors and a capacitor. In this circuit no any timer ic is used , so the construction of this project is easy. 

timer circuit diagram with relay gif

on Delay timer circuit for switch ON

Use at least minimum 2200uf 25v capacitor and connect a 5.6k ohm resistor to parallel of this capacitor for discharging fastly . When switch on the circuit then capacitor start charging and amount of power go to the capacitor till charge, after some seconds it get fully charged. After capacitor get fully charged then the current starts to go to the PNP transistor BC558 and through 100k resistor at base of this transistor , it get turn on and then the supply passed through this transistor and goes to the NPN 2N2222A through 1k resistor and preset. And this transistor is also turn on and the Connected relay is activated now.The Timing delay produced by the charging time duration of capacitor. When switch off this circuit, the capacitor is discharged and it ready for next time provide delay time.

Adjust the preset according to the output , and check the circuit with a PCB relay .  Preset should adjusted at that point which get sufficient current output that is able to activate the relay. I suggest use a small size PCB Relay of 12v 20A. i am also provide a simulation video of this circuit. If you want more time duration then connect more that 2200uf value capacitor or connect more with parallel .

simulation video


In real practical use timing  duration may vary.



Capacitor 2200uf 25v-1


5.6k -1






Diode- 1N4007-1

12v PCB 20A Relay-1

About the Author


Hi, My name is Aman Bharti, I am interested in making and study of Electronics & circuit diagram. I like to share my knowledge and all ideas with people which I get from My Experiment & from different sources. I try to provide any circuit details deeply with test results as possible. You can contact me on- Email – [email protected]

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