Towards a first time right design of the common mode choke

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 new equivalent circuit of the component is proposed where impedances are related to the designable parameters of the choke. This equivalent circuit is 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. Sensitivities and deviation studies give additional insight on the behavior of the filter once it is placed in the practical system. The new common mode current flowing in the circuit after the insertion of the choke can then be evaluated without a ‘cut and try’ process.