Analysis of the Function of Parallel Diodes in Relay Coils 2

The magnitude of the back electromotive force is related to the rate of current change and the inductance of the coil, and its direction is opposite to that of the original current. It may cause damage to other components in the circuit, especially semiconductor components. To suppress the impact of this back electromotive force on the circuit, a diode is often connected in parallel across the relay coil. This diode is commonly referred to as a freewheeling diode or flyback diode.diode

The diode connected in parallel across the relay coil is in reverse bias during normal operation and does not affect the relay coil's functioning. When the relay is de-energized, the sudden interruption of current in the coil generates a back electromotive force (EMF) that forward biases the diode. At this point, the diode conducts, forming a loop through which the back EMF-induced current flows via the diode and the coil. This effectively limits the back EMF to a lower level, mitigating its impact on other parts of the circuit.diode

When connecting diodes in parallel, their orientation must be carefully considered. The correct method is to connect the anode of the diode to the negative terminal of the relay coil and the cathode to the positive terminal. This ensures that the diode is reverse-biased during normal operation, preventing interference with the relay's function. When the relay is de-energized and generates back EMF, the diode becomes forward-biased, effectively conducting the current produced by the back EMF.diode

The main advantages of using diodes in parallel with relay coils include