Method for Reducing Surge Voltage and Turn-on Loss in Push-pull DC-DC Converters

Abstract

This paper proposes a new method to suppress surge voltage on diodes used in the rectifier circuit of push-pull type DC-DC converters. In cases in which the rectifier circuit is connected to the center-tapped winding of a transformer, a large surge voltage amplitude appears on the rectifier diodes, owing to commutating operations. Conventionally, an RC-type snubber circuit is connected to the diodes; however, this results in large amounts of power loss on the snubber circuit and causes a significant reduction in the overall conversion efficiency of the power converter. In order to overcome these problems, this paper proposes a new surge suppression method. In this method, the magnetizing current flowing in the secondary winding of the transformer is transferred to the primary winding during the commutating period, and the current flowing through the output capacitance of the rectifier diode to turn off is absorbed. Hence, the surge voltage on the rectifier diode is reduced, and the surge voltage on the switching devices connected to the primary winding of the center-tapped transformer is also reduced. The effectiveness of the proposed method is verified through a 3kW experimental setup; a high efficiency rate of 98.5% was achived, and surge voltage was minimized on all switching devices.