High-speed switching operation of MOSFETs using auxiliary circuit shorting load

This paper describes a high-speed switching technique of power MOSFETs applied to a chopper and a half-bridge inverter. The switching time must be shortened to operate power converters using the power MOSFETs at high-frequency, but parasitic output capacitance prevents the MOSFETs from turning off fast. In general, the turn-off time becomes longer as a load current is reduced because the reduced drain current takes a long time to charge the parasitic output capacitance. In the paper, a set of auxiliary switches and diodes in parallel with a load is proposed to reduce the turn-off time effectively. This additional auxiliary circuit makes a high-frequency drive of the power MOSFETs and switching-loss reduction of the power converter possible. It has been confirmed through experimental tests that the operational frequency range of the power converter expands to MHz-order and that the power conversion efficiency is effectively improved in a low-load range by employing the proposed technique.