DC Side Snubber Circuits

For diode assemblies in bridge configurations it is normally enough to add a snubber to the DC side if the diode assemblies are not already connected to a low-inductance voltage DC link. The resistors and capacitors are rated depending on whether the surge voltages to be attenuated are on the AC or DC side. If there is any possibility of the rectifier being conductive even when the load is turned off or disconnected, a discharge resistor has to be used. In rectifiers with permanent capacitive load, this load will function as an overvoltage snubber, meaning that no additional snubber circuits are needed. If, on the other hand, there is a ripple filter choke or fuse between the rectifier and capacitive load, a snubber circuit for overvoltage will have to be integrated directly at the rectifier in addition.

For diode assemblies in midpoint configurations, it often makes sense to add an auxiliary half bridge with small auxiliary diodes. Such snubbers do not provide protection from overvoltages that affect the rectifier from the DC side.

In thyristor assemblies, an AC-side snubber and single-switch snubbers will normally be integrated, which means the use of a  DC snubber can often be dispensed with.

For more information, please read:

Protection of Thyristors with Snubbers

Snubber Circuits Based on Silicon Avalanche Diodes