Novel Techniques to Suppress the Common-Mode EMI Noise Caused by Transformer Parasitic Capacitances in DC–DC Converters

This paper proposes novel electromagnetic interference (EMI) suppression techniques for dc–dc converters. For low-voltage high-current applications, windings are paralleled and interleaved. Although low conduction loss and low leakage inductance can be achieved, the winding capacitances are considerably increased, thereby deteriorating the converter's EMI and soft-switching performances. To solve these problems, a novel balanced choke concept is proposed, as well as other techniques. The advantages of the proposed concepts and strategies are verified and demonstrated on a 1-kW 1-MHz 400-V/12-V$LLC$resonant converter prototype. More than 52-dB noise attenuation and 75% equivalent winding capacitance reduction are achieved. Hence, EMI and soft-switching performances are significantly improved.