An Active Common Mode EMI Filter for Switching Converters

Conducted electromagnetic interference resulting from common mode noise currents are a significant problem with switching power converters. Such noise current arises as result of the broadband nature of the switching waveforms that are coupled into the ground through parasitic capacitive paths. It is common to employ passive LC-filters to mitigate common mode noise keeping the noise levels below applicable regulatory limits on emissions. The work presented herein focuses on a circuit configuration including active components that aids the LC filter to suppress external common mode emissions. The paper presents a qualitative development, design oriented analysis of the proposed approach and experimental evaluation verifying its performance.