Characterization And Cancellation Of Parasitic Parameters For EMI Filters

Electromagnetic compatibility (EMC) design has been one of the most important components during the research and development process of power converters with switching power supplies increasing. Meanwhile, relevant standards of EMC have been a target which power converters should satisfy. EMI filter Applied is one of the most effective means for conduction interference suppression, but due to the parasitic parameters of EMI filter, ordinary EMI filter is not very effective in suppressing interference produced by typical power converters. Therefore, it is essential to extract and eliminate parasitic parameters of EMI filters.Firstly, the insertion loss is discussed in particular detail and measuring method is introduced. Scattering parameters are chosen to characterize EMI filters because they are easy to measure in the high frequency rang. All S-parameters are measured directly by network analyzers. S21 is also the so-called transfer gain when source and load both are 50?. And then, the impact of parasitic parameters play different roles in high-frequency characteristics by analyzing relationship between the insertion loss and self-parasitic or mutual parasitic parameters of EMI filters. So the parasitic parameters can be targeted to extract and eliminate. The models of common mode choke in EMI filter are built based on the relationship between parameters of inductor model and frequency, and the parasitic parameters of capacitors are extracted with the impedance parameter method. Finally, the agreement of measurement and calculation results validates the model and confirms the method of parasitic extraction.In order to improve high-frequency performance of EMI filter, of which parasitic parameters must be eliminated. The principle of cancellation and secondary capacitance are analyzed, and the eliminator using PCB windings interlaced is introduced. The 3D finite element model is presented and the comparison of the calculated and measured mutual inductance validates the modeling method. The cancellation of parasitic capacitance for inductors is analyzed in the paper, and such inductors with bifilar windings in series is greatly improved the filtering performance. Finally, the parasitic parameters of EMI filter are eliminated, which is applied to a 250W Boost PFC converter. The conducted interference is reduced contrast in high frequency.