A simple EMI filter design method in communication power supplies

This paper presents an improved and simplified method to design electromagnetic interference (EMI) filters for communication power supplies. Based on the measurement of the maximum and the minimum differential mode (DM) and common mode (CM) EMI noise source impedance, a method is proposed to suppose the noise source as current source and calculate the magnitude of DM and CM noise source current. Then EMI filter is designed according to the magnitude of noise source current. The proposed method is easy to apply in practice without considering the topology and control method of the power supply. The calculated and experimental results of a 600W prototype show the method is feasible to guarantee to satisfy requirement, especially at low frequency.