Single power stage ac/dc forward converter with power switch voltage clamping function

Abstract

A method and circuit for clamping a voltage across a switching element in a forward converter circuit to a value equal to or less than the DC bus voltage. The disclosed circuit and method achieves voltage clamping in a circuit configuration in which two series connected direct current (DC) bus capacitors are connected in parallel with a switching element to be clamped. Clamping is further achieved by selecting capacitor values to be sufficiently large so as to maintain a constant voltage throughout each switching cycle of the switching element. The capacitors serve a second function in that they recover energy stored in the windings of an isolation transformer which would otherwise be dissipated in a conventional circuit design.