High-Frequency Equivalent Circuit of a Ferrite Common Mode Choke Considering DC Superimposition Characteristics

In this study, we propose a high-frequency equivalent circuit model of common-mode chokes with consideration of the DC superimposition characteristics. Such a model is particularly crucial for predicting the degradation of the noise attenuation characteristics of electromagnetic interference filters due to magnetic saturation in the design stage. The proposed model is a parallel circuit that comprises an inductor with a DC current dependence and an equivalent circuit without such a dependence. A simple formula with only three fitting parameters is used to model the DC superimposition characteristics at low frequencies, and vector fitting techniques are adopted to model the complex impedance characteristics at high frequencies. This paper describes the full modeling procedure and presents an equivalent circuit in LTspice. The accuracy of the model is verified by experiments using one-turn coils with Mn-Zn and Ni-Zn cores. Good agreement is obtained under various DC bias currents.