Novel techniques to suppress the common mode EMI noise caused by transformer parasitic capacitances in DC-DC converters

This paper proposes novel 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 performance. 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 1kW, 1MHz, 400V/12V LLC resonant converter prototype. More than 52dB noise attenuation and 75% winding capacitances reduction are achieved. Hence, EMI and soft switching performance are significantly improved.