Phase-shifted bridge with auxiliary circuit to maintain zero-voltage-switching

A phase-shifted PWM dc-to-dc converter includes a pair of switched half-bridges defining taps. The primary of an output transformer is coupled across the taps to receive AC, and produces transformed AC which is rectified and filtered to produce the output dc. Zero-voltage-switching (ZVS) is maintained over the full range from zero load current to maximum load current by the use of an auxiliary circuit including an "inverting" second transformer having primary and secondary windings serially coupled with capacitors. The primary-capacitor serial circuit is connected between a first half-bridge tap and reference potential, and the secondary-capacitor serial circuit is connected by an inductance between second half-bridge tap and a reference potential.