Concept to reduce the ringing during the discontinuous mode of a DC/DC converter

Abstract

When a converter changes into the discontinuous mode, a ringing starts across the semiconductors. This is caused by the necessary voltage step across them and the necessity to charge the parasitic capacitors of the devices. To reduce this swinging, another strongly coupled winding is applied to the magnetic device of the converter. By shunting this winding, when the active switch and the passive switch of the converter are turned off, the ringing is significantly reduced. The method is explained and applied to the buck, the boost and the combined forward-flyback converters. Simulation and experimental results for a small boost converter are shown.