A delayed pull-in relay circuit diagram

If you want to obtain a long-term and easily adjustable delay circuit, the relay current should be controlled by a transistor, and an RC link should be connected to the base circuit, as shown in the figure. If the power supply voltage, capacitance C, current amplification coefficient β and the required pull-in power are all known, the appropriate relay coil resistance value and operating voltage value should be selected to make the delay time as large as possible. This time can be obtained by The time constant value is determined. As shown below: