How to suppress reverse EMI in EPS relay coils?

In EPS (Electric Power Supply), the relay or contactor coil generates a high reverse electromotive force (reverse peak voltage) due to its inductive characteristics at the moment of de-energization, creating strong transient noise that may interfere with the control circuit or even damage the drive transistor. The main method to suppress reverse peak EMI is to connect a freewheeling (absorption) element in parallel with the coil:

1. Reverse diode: Connect a diode in parallel across the coil (cathode connected to the positive power supply) to provide a freewheeling path for the reverse peak current and clamp the voltage. This method is simple, but the coil current decays slowly, and there is a delay in relay release.

2. RC snubber circuit: Connect a resistor and capacitor in series in parallel across the coil. This circuit can more effectively absorb energy and accelerate current decay, reducing contact arcing, but it will generate some losses.

3. TVS diode: Connect a bidirectional TVS diode in parallel, such as the SMBJ series, to quickly clamp the reverse peak voltage to a safe value. Generally, RC or TVS solutions are superior to single diodes in suppressing high-frequency EMI.