Simple spread-spectrum pulse-modulation technique for EMI mitigation in power converters

The adoption of wide-bandgap (WBG) switching devices such as gallium nitride (GaN) transistors in power converters enables to achieve higher switching frequencies and higher power density with reduced cooling requirements and smaller passive components. However, the potential for increased electromagnetic interference (EMI) resulting from the faster switching transients possible with WBG devices is a concern in many applications. Hence techniques for reducing EMI are of increasing interest. In this paper we present a simple implementation of a spread-spectrum pulse-modulation technique to reduce the peak EMI generated by switch-mode power converters. The method is based on an aperiodic gate drive signal generated from two periodic signals, e.g. a sawtooth and a sinewave, which are anharmonically related. Simulations and experimental measurements of conducted EMI from a prototype of a SEPIC converter incorporating a hybrid GaN HEMT demonstrated a 10 dB reduction in peak EMI.