Winding Optimization for Reducing Parasitic Capacitances of Common-Mode Chokes

Parasitic capacitances typically undermine the filtering performance of common mode chokes at high frequencies. This work demonstrates that these parasitic capacitances can be reduced by using a wise winding strategy that depends on the physical properties of the core material. Due to its practical interest, we specifically focus on single-layer common mode chokes wounded on NiZn or MnZn ferrite cores. Based on a physical model that enables the identification of parameters influencing the electrical coupling between the turns of the coils of the choke, the hypothesis proposed is that the optimal winding configuration depends on the core material, differing for NiZn and MnZn cores. To verify this hypothesis and to assess improvements actually achieved by optimum winding strategies, an accurate high-frequency model of the common mode choke along with an efficient characterization technique are used to numerically estimate the parasitics of common-mode chokes with different core materials and winding configurations. In addition, the filtering performance of these common mode chokes have been measured and compared.