Filter circuit

 Filter circuit 

If the surge exceeds the normal ±180 volt peak dynamic range of the power wave, the dynamic clamp circuit (D1 C3) which tracks the peak of the power wave comes into play

Placing a diode in reverse bias in parallel to the load eliminates voltage spikes by going into conduction before a large voltage can form across the motor. And this is how a DC transientvoltage

 suppressor circuit works to eliminate 

harmful voltage spikes.

The filter circuit is used in spike

 guard to filter out the power spikes and  protect against power surges

Capacitor 

A

The capacitor allowsalternating current (AC) to pass but it blocks direct current (DC).