CM Noise Reduction with Symmetric Topology
CM choke is dominating the EMI filter size for most converters. Topologies with low CM noise are very attractive from this point of view. It is well known that symmetric topologies have low CM noise. However, there is lack of modeling and criteria for a symmetric topology. CPES has studied the symmetric boost converter and developed its CM noise model. Important parasitics are included. Analysis and experiments show that parasitics affects both low and high frequency CM noise. Methods are proposed to achieve symmetry including the parasitics. CM noise can be greatly reduced. This modeling technique can be also applied to other symmetric topologies such as symmetric bridgeless PFC converter and two switch forward converter.