Switching-aid Circuits with Energy Recovery

Abstract

Turn-on and turn-off snubber circuits for the bipolar transistor and the gto have been considered in chapters 7 and 8. These snubber circuits modify the device V-I switching trajectory and in so doing reduce the device transient losses. Snubber circuit action involves temporary energy stored in either an inductor or capacitor. In resetting these passive components it is usual to dissipate the stored energy in a resistor as heat. At high frequencies these losses may become a limiting factor because of the difficulties associated with equipment cooling. Instead of dissipating the switching-aid circuit stored energy, it may be viable to recover the energy either back into the supply or into the load. Two classifications of energy recovery circuits exist, either passive or active. A passive recovery circuit involves only passive components such as L and C. while active recovery techniques involve switching devices, as in a switched-mode power supply.