EMI filter design method for communication power sub-system

This paper introduces an improved and simplified method to design EMI filters for switching power supplies (SPS), for both AC-to-DC and DC-to-DC. This method is based on using an engineer´s way to measure the maximum and the minimum differential mode (DM) and common mode (CM) EMI noise impedance, and consider them in designing the EMI filters. Information of the topology and control method of the power supply is not needed. This method solves the limitations of the old EMI filter design methods, which are either too complicated to use, or based on ideal cases. The analyses and experimental results show that this method can guarantee that the required attenuation can be achieved, especially at low frequency.