Capacitor as timer circuit1/3/2024 In the Darlington pair of transistors, the base of the 2nd transistor will get a small voltage from the emitter of the 1st transistor. this combination of two transistors is called the Darlington pair. Transistor Q1 will get a small voltage at its base terminal for turning on and this single transistor gives very less current that not be able to activate the relay so another transistor is connected with the emitter of the first transistor to make high output current. 56K resistor is used in the circuit for the discharging of capacitor C1. This circuit is working on the charging and discharging duration of capacitors. If you want more time duration then connect more than 2200uf value capacitor or connect more with parallel. I suggest using a small size PCB Relay of 12v 20A. When switch off this circuit, the capacitor is discharged and it ready for next time to provide delay time. The Timing delay is produced by the charging time duration of the capacitor. And this transistor is also turned on and the Connected relay is activated now. After the capacitor gets fully charged then the current starts to go to the PNP transistor BC558 and through the 100k resistor at the base of this transistor, it gets turned on, and then the supply passed through this transistor and goes to the NPN BC548 through 5k resistor. When switching on the circuit then the capacitor starts charging and the amount of power goes to the capacitor till charge, after some seconds it get fully charged. Use at least a minimum 2200uf 25v capacitor and connect a 5k ohm resistor to the parallel of this capacitor for discharging fastly.
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