An Active EMI Filter for High-Power Off-Line Applications

This digest presents an integrated active EMI filter (AEF) solution that mitigates conducted common-mode (CM) emissions and improves power density in kilowatt-scale off-line power supplies. The proposed AEF solution comprises an integrated circuit (IC) that senses high-frequency CM noise from the power lines using a set of Y -rated capacitors, while rejecting line-frequency and differential-mode components. The IC processes the sensed CM noise and injects a cancelling current back into the power lines through another Y-rated capacitor, hence presenting a very low impedance to CM noise and emulating a much larger capacitance that allows choke inductance to be reduced. A damping network external to the IC is placed in the injection path to stabilize the closed-loop system. Analytical formulations are presented to evaluate the performance and stability of the proposed AEF. The AEF is experimentally validated with a totem-pole power factor correction converter. It is shown to provide up to 25 dB reduction in CM noise, which enables the chokes of the EMI filter to be reduced in size by 55% while maintaining similar EMI performance.