0 Delay Switch using Transistor

This simple delay switch is made up only by transistors and has very minimal parts. The function of this circuit is the combination of delay on switch circuit and delay off circuit, but much simple compared to the two. This project is very helpful in delay off or on in the car lighting system and other device powered by 12V battery.

Circuit Operation
Initially, the lamp is off and capacitor has no charge. At the moment the switch SW is closed, the capacitor charges and the voltage across it increases at a rate dependent primarily to the value R1 and C1. When the voltage across C1 is enough to trigger the transistor Q2, the lamp starts to light up. The same thing happens when the switch is open, the capacitor discharges to R4. When the voltage across the capacitor is drops, the Q2 turns off. Thus increasing the values of R1 and C1 increases the delay of turning the circuit ON (4 sec) while C1 and R4 combination determines the delay in turning the circuit OFF.

delay switch schematic
Part List:
R1  - 22 kilo ohms 1/4W
R2 - 120 kilo ohms 1/4W
R3 - 56 kilo ohms 1/4W
R4  - 47 kilo ohms 1/4W
C1 - 47uF electrolytic capacitor rated 16V
Q1 - 2N2222, 9014, 9013 or similar NPN transistor
Q2 - IRF530 or any NMOS minimum current 5A
SW - any switch available
Lamp - lamp or any DC devices

Part Pinout: Click to diagrams to enlarge
IRF530 pins
2N2222 and NPN transistor pins


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