Application note
AN0014Optimizing HV Contactor Coil Suppression
Why aggressive coil clamping protects driver electronics but slows contact separation and shortens HV contact life.
Summary
Contactor longevity is closely tied to the mechanical velocity of contact separation during de-energization, which is in turn affected by how the coil's inductive energy is suppressed. When a contactor coil is de-energized, the stored magnetic energy creates a Back EMF spike that can reach several hundred volts, and many designers instinctively clamp it as aggressively as possible to protect driver FETs and PLCs. This application note explains that aggressive suppression using standard rectifier diodes clamps the spike near zero but traps recirculating current in the coil, slowing contact separation and reducing high-voltage contact life. It details the critical balance between protecting driver electronics and preserving the mechanical performance needed for reliable arc interruption.
