Analysis and Reduction of Radiated EMI in High-Frequency GaN IC-based Active Clamp Flyback Converters

This paper investigates radiated electromagnetic interference (EMI) causes and solutions in high-frequency active-clamp flyback (ACF) using GaN ICs. GaN devices enable high-frequency operation which shrinks the passive component size and can potentially be more efficient. However, the increased spectrum of radiated EMI is a concern with a lack of readily-available solutions. This paper analyzes noise mechanisms by studying waveform and spectrum compositions, identifying major noise contributors. Near field couplings of the cable-converter electric couplings are identified as inducing the CM noise and bypassing the CM choke. This paper develops models to characterize the near field coupling effects on the radiated EMI. Noise reduction techniques including a shielding and grounding technique, a CLC pi-type CM filter are proposed and verified. Experimental verifications are performed on a GaN IC-based ACF power adapter and radiated EMI is brought into compliance.