Improving differential mode inductance in toroidal common mode inductors

Toroidal inductors are widely used in switch mode power supplies to attenuate electromagnetic interference (EMI). However, conventional common mode (CM) inductors have limitations in achieving differential mode (DM) noise attenuation and may introduce near-field coupling. In this paper, the advantage and disadvantage of conventional CM inductors are investigated. An integrated inductor scheme is proposed to overcome the limitation. The proposed scheme maintains the same CM inductance as conventional toroidal CM inductors while significantly increasing the DM inductance and reducing leakage flux. This leads to reduced weight and size of discrete DM inductors and enables higher power density of the converter. The theoretical analysis is conducted using the equivalent magnetic reluctance model. Further validation is performed through 3D finite element method simulations, insertion loss measurements, and CM and DM noise spectrum measurements. Results demonstrate that the proposed integrated inductor scheme offers superior EMI performance compared with conventional CM inductors.