In situ performances of common mode chokes

There is a need for an analytical model of the EMI filter relating its designable parameters to its final performances in the circuit. The final goal of the model presented here, is to support a first time right design of the common mode choke. A key aspect of such a model starts with the selection of the core material which is reviewed in the first section. A new equivalent circuit of the common mode choke is proposed in the second section and each of its impedances is related to the designable parameters of the choke. This equivalent circuit is finally inserted in a global model of the output of the converter where the actual performances of the choke can be evaluated via a modification factor of the common mode current. All models introduced are validated with measurements. The new common mode current flowing in the circuit after the insertion of the choke can then be evaluated without ‘cut and try’ process.