Energy-saving circuit using relay self-induction energy

Energy is becoming increasingly expensive. Therefore, when designing circuits, we often want to find a way to save energy. Therefore, it was decided to find a way to save power in the relay switching circuit.

As shown in Figure 2a, the relay is driven by a transistor T1, and a freewheeling diode D1 is often connected in parallel to the relay coil RE1. When the relay circuit is closed, the freewheeling diode D1 can short-circuit the back electromotive force generated by the relay coil RE1. As shown in Figure 2b, the LED (D2) is connected in series with the freewheeling diode D1. When the transistor T1 is turned off, the induced current will cause it to flicker. The time and brightness of D2 light are determined by the current change rate and self-inductance of the relay coil. u=-L di/dt. In fact, it is necessary to judge whether the induced current will damage the LED.

So far we have not conserved power, Figure 2c illustrates theoretically how the power generated by the relay coil can be saved and used to power other circuits. If a relay coil with a larger self-inductance is used and is frequently switched on and off, more electrical energy will be stored in capacitor C1. Zener diode D2 connected in series with freewheeling diode D1 limits the maximum capacitor charging voltage. Measure the voltage at point A to ground, which is the sum of the capacitor voltage Uc and the supply voltage Ub. It should be noted that the voltage at point A is slightly higher than the supply voltage.