Transient suppression of relay coils
When the relay coil is de-energized, the inductive energy stored in it may generate a surge voltage of up to 1500V on the DC power line. As the use of solid devices continues to increase, the relay coil must be suppressed to limit its voltage peak to a certain level Scope.
Common coil transient suppression methods include: a resistor or RC circuit in parallel with the coil, or a diode in parallel. The coil transient suppression circuit will prolong the relay release time and slow down the contact switching speed.