Zero-voltage-transition converter with low conduction losses operating at constant switching frequency

A soft-switching buck converter with duty-cycle control is proposed. Compared to its hard-switching PWM counterpart, the new switch-mode converter contains four additional elements: a resonant inductor, an active switch and two diodes. The parasitic capacitances of the main and auxiliary active switches serve as resonant capacitors. Multiresonance is created in the circuit, thus allowing for zero-voltage-switching of the active switches and rectifier diode. The commutation of all switches takes place with zero capacitive turn-on losses; consequently, the switching losses are small. The current through the resonant inductor is not allowed to increase over the load current; the resonant stage is delayed until the inductor has been discharged. As a result, the voltage and current stresses on the devices are at the same level as on their counterparts in conventional converters, implying normal-rated switches, and normal conduction losses. The overall efficiency is very high, as proved by the measurements on a prototype realized in the laboratory