Effect of Magnetic Couplings on Conducted EMI of GaN-Based PFC Converter

Wide-bandgap power devices have enabled power supplies to increase in density while maintaining high efficiency. However, EMI issues remain one of the most challenging aspects when designing a power converter. These issues are often caused by parasitic near-field couplings which can degrade or bypass the attenuation of the EMI filter. This paper investigates how parasitic magnetic couplings impact the conducted noise of a high-frequency PFC converter using PCB-winding inductor. Analytical models are presented for both differential mode (DM) and common mode (CM) noise, including the effects of magnetic couplings between the PFC inductor and EMI filter. Then, three ferrite inductor core designs are evaluated to demonstrate how the core’s geometry and permeability affect its leakage magnetic field. Choosing the optimal core design is shown to significantly reduce the magnetic field outside the PFC inductor, which reduces DM noise by more than 20 dB and reduces CM noise by 7 dB.