A high-efficiency 1.5 kW, 390-50 V half-bridge converter operated at 100% duty-ratio

A half-bridge isolated step-down converter operated at nearly unity duty-ratio for very high efficiency is discussed. It is meant to interface the 390 V regulated output of a 1.5 kW power factor correction unit to a 50 V distribution bus. It is based on the zero-voltage switching (ZVS) scheme of the phase-shifted pulse width modulation (PWM) approach, but since the duty ratio does not vary from near unity, the output inductor is omitted. The ring of the output rectifier capacitance with the transformer leakage inductance is therefore clamped by the output capacitor, which permits the oscillation energy to be recovered. This, together with ZVS of the MOSFETs, gives the converter an efficiency greater than 95% at full load