Using a transistor to make a power-up delay relay

A relay is an electronic control device that has a control system (also called an input loop) and a controlled system (also called an output loop). It is usually used in an automatic control circuit. It actually uses a small current to control the larger. An "automatic switch" of current. Therefore, it plays the role of automatic adjustment, safety protection and conversion circuit in the circuit. Reduces energy consumption by automatically delaying the closing time of the load; increasing user comfort (for example, ON-OFF switches control both lighting and ventilation); time-delay relays are an alternative to conventional industrial relays, and modular construction offers additional benefits.
This circuit takes advantage of the base breakdown voltage of the emitter/an ordinary bipolar transistor. A 2N3904 transistor at the emitter/base junction of the reverse connection acts as an 8 volt Zener diode which creates a higher turn-on connection to the Darlington transistor pair voltage. Almost all bipolar transistors can be used, but the Zener voltage will likely be about 6 to 9 volts for a particular transistor used. The time is approximately 7 seconds delay using a 47K resistor and a capacitor of 100uF, which can be reduced by reducing the R or C value. A longer delay can get a larger capacitor, and the time of the resistor should not increase by 47K. The circuit should work with any 12 volt DC relay, with a 75 ohm resistor or multiple coils. The 10K resistor provides a power-off when the entire supply connection is not needed, and if the power supply already has a bleeder resistor, the capacitor discharges the path.