匝数不对称的环形共模电感特性分析

Analysis of toroidal common-mode inductors with asymmetric number of turns

共模电感会产生磁场泄漏,其漏感可以被用作差模感量。分别对匝数对称共模电感与匝数不对称共模电感进行磁路建模,发现匝数不对称共模电感在磁芯磁材的截止频率前可以进一步增加其差模感量。提出一种差共模电感集成方案,将两个匝数不对称的共模电感串联堆叠,同时保持L、N线路之间的阻抗平衡。有限元仿真表明,所提方案能够显著增加共模电感的差模阻抗,并降低磁场泄漏。实物测试中,所提方案的阻抗为传统方案的1.5~8倍。插入损耗测试结果显示,在100 kHz~10 MHz范围内,所提方案相比传统方案能够增加8~20 dB的插入损耗,验证了所提方案能够明显改善EMI滤波器的滤波效果。

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.