High frequency self-oscillating inverter with negligible switching losses

Abstract

A high frequency self-oscillating inverter including a snubber circuit for minimizing both turn-on and turn-off switching losses. The inverter converts a DC supply to an AC load current and includes a saturating transformer for alternatively driving first and second switching devices during subsequent unsaturated states. During the time the transformer is saturated, both switching devices are kept off. The snubber circuit includes a first capacitor across the first switching device, a second capacitor across the second switching device, and an inductance. During saturation the two capacitors and inductance form a resonance circuit, wherein the inductance has a resonant half sine wave current, one capacitor discharges, and the other capacitor charges. Turn off switching losses are made negligible by selecting capacitors such that the fall time of the corresponding switching device is much faster than the time to charge the capacitor to a significant voltage. Turn on switching losses are made negligible by having the capacitor across the on-going switching device discharge to approximately zero during saturation before the transformer returns to an unsaturated state to turn-on the on-going switching device.