This paper presents the analysis and design of a hybrid EMI filter for an active clamp GaN MOSFET flyback SMPS. SMPS WBG switches are increasingly used due to their high switching speed and frequency capabilities. However, these switches could emit considerable CM EMI at high-frequency operations. Passive EMI filters (PEF) are commonly employed, comprising bulky CM chokes. Active EMI filters (AEF) have been introduced to improve this aspect. However, the impact of parasitic parameters has been limitedly explored. To address this, the effect of sensing capacitor parasitic parameters is discussed and mathematically presented, which is one of the major bottlenecks. With the new understanding, this digest proposes a hybrid EMI filter comprising an active EMI filter (AEF) and a PEF. Integrating AEF considerably decreases CM choke size. HEF design considerations are discussed with simulation and mathematical analysis. Experimental study is conducted to validate the proposed filter design.
