Silicon Laboratories Inc.
Clamping inductive flyback voltage to reduce power dissipation

Abstract:

A switch controls current to be supplied to an inductive load when turned on. A clamp circuit clamps a flyback voltage resulting from turning off the switch. The clamp circuit has a first clamping voltage responsive to the switch being turned off, and has a second clamping voltage, higher than the first clamping voltage, responsive to a current level through the inductive load being lower than a predetermined current level. That ensures that as the current comes down to levels required to break contact, the clamp voltage is increased to speed the collapse of the magnetic field when needed to minimize contact wear by maintaining armature momentum.