Analysis of toroidal common-mode inductors with asymmetric number of turns
Common-mode (CM) inductors generate magnetic field leakage,which can be used as differential-mode (DM) inductance. The magnetic circuit models were established for the turn-symmetric and turn-asymmetric CM inductors,respectively. The results show that the turn-asymmetric CM inductor has higher DM inductance below the cut-off frequency of the magnetic material than the turn-symmetric one. A scheme was proposed to integrate the CM and DM inductors,where two asymmetric CM inductors were connected in series and stacked. The scheme can maintain the impedance balance between the L and N lines. The finite element simulations verify that the proposed scheme can significantly increase the DM impedance of the CM inductor and reduce its magnetic field leakage. In experimental test,the impedance of the proposed scheme was 1.5-8 times higher than that of the conventional scheme. The measured results show that the proposed inductor could achieve higher insertion loss by 8-20 dB from 100 kHz to 10 MHz than the traditional scheme,which verifies that the proposed scheme can significantly improve the noise filtering of the EMI filter.
asymmetriccommon-mode inductorEMI filtermagnetic field leakagenear-field couplinginsertion loss
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