A Transformer-Isolated Common-Mode Active EMI Filter Using a Low-Cost BJT Amplifier with Feedforward Structure

This paper proposes a fully transformer-isolated feedforward current-sense current-compensation (CSCC) active EMI filter (AEF). The proposed AEF is estimated by circuit analysis, and a design guide is developed. The proposed AEF can be implemented with a low-cost BJT amplifier and operated in an independent low voltage dc supply. The noise attenuation performance of the proposed AEF is verified by using simulation and vector network analyzer (VNA) measurement. The proposed AEF achieves additional CE noise reduction up to 30dB at frequency range from 150kHz to 3Mhz.