Inductor Winding Capacitance Cancellation for Flyback Converters without Grounding Paths

As the switching frequency of power converters is increased to achieve high power density, the high frequency common mode (CM) EMI noise becomes a severe challenge. The inductor equivalent parasitic capacitance (EPC) cancellation technique was proposed to improve the high frequency performance of CM inductors. Although it was verified in separate inductors, few papers are addressing its application within power converters. This paper first reviews the EPC cancellation technique and the common mode noise model of an isolated Flyback power adapter. The CM inductor EPC cancellation technique without using grounding paths is proposed. Two filter topologies are discussed. A technique to conveniently evaluate the performance of EPC cancellation in a power adapter with a network analyzer is proposed. Experiments were conducted to verify the techniques.