Significance of critical components placement to control EMI in power supplies. A case study

According to the power rating of a system, larger circulating current (I), high frequency (F) switching and also larger loop area (A) due to thicker cables, are involved in power supplies. Since EMI is directly proportional to I/spl times/A/spl times/F, the noise level would be larger in higher power rating systems than lower ones. Now, the reduction of conducted emissions (EMI) by use of any power line filter ("brute force method") is only capable of reducing EMI to certain degree, because of its size, weight and cost restrictions. Hence the cost effective technique for reducing EMI (conducted and radiated emissions) is to suppress them at their source while retaining the desired functional performance of the system. This paper describes various methodologies adapted such as identifying the major culprits, victims and coupling, to reduce the EMI level to prescribed limits in a 1 kVA/48 V DC inverter. Attention is paid to the importance of location of critical components and routing of wires (i.e. packaging of the system) within a system for achieving EMC.