Parasitic Impact Analysis and Design of Hybrid EMI Filter for Active Clamp Flyback SMPS

This paper presents the impact of parasitic elements on the design and performance of an active EMI filter (AEF) for an active clamp GaN MOSFET flyback switching mode power supply (SMPS). SMPS with wide-bandgap (WBG) power switches are increasingly used due to their high switching speed and frequency capabilities. However, extremely high-frequency operations of these switches lead to considerable common-mode (CM) electromagnetic interference (EMI) generation. Passive EMI filters (PEF) are commonly employed, comprising bulky CM chokes to mitigate CM EMI. To increase power density, Hybrid EMI Filters (HEF) have been introduced, where AEFs work in conjunction with PEFs. However, current transformerless AEFs use multiple passive components to sense and cancel noise signals and their attenuation capabilities are severely limited by the parasitic parameters of these passive elements. This is a crucial aspect in AEF and HEF design which has been limitedly explored in the existing literature. To address this research gap, , which is one of the major bottlenecks in AEF bandwidth limitation, the effect of injection and sensing capacitor parasitic parameters is mathematically presented and experimentally validated in this paper. The HEF design considerations are discussed with simulation and mathematical analysis. Experimental studies are conducted to validate the proposed filter design and show the effects of parasitic elements on the bandwidth of AEF and HEF, and their CM EMI attenuation capabilities.