the invention prevents the voltage change ratio of switching devices of a power converter from exceeding a specified maximum rating , thus avoiding damage in switching devices and an increase in conduction loss . in a power converter having a plurality of switching devices , switching means for switching a control scheme for the switching devices to a phase shift control scheme or a pulse width modulation scheme is provided , whereby the control scheme for the switching devices is switched from the phase shift control scheme to the pulse width modulation scheme in a non - load or light - load state .