Sandwiched winding is widely used in transformer design due to its low AC resistance and small leakage inductance. However, the expansion of winding coupling area causes the increasing of common mode (CM) electromagnetic interference (EMI). Shielding method is the most effective way to reduce coupling inside the isolated transformer. Yet the foil shielding design of sandwiched winding transformer has rarely been involved, for purpose of suppressing the CM EMI in flyback converter. In this work, we propose a method to determine the optimal width of a double-layer foil shielding in the primary-secondary-primary sandwiched winding transformer, for minimizing the conducted CM EMI of flyback converters. The equipotential distribution and the structural capacitance are analyzed, and the model of equivalent CM capacitance is established to calculate the minimum CM current flowing through the sandwiched winding transformer. The proposed method is validated through comparison of calculated and measured results.

中文翻译：

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为减小反激式转换器的共模EMI，夹层绕组变压器屏蔽箔宽度的确定

夹层绕组因其交流电阻低、漏感小而广泛用于变压器设计。然而，绕组耦合面积的扩大导致共模（CM）电磁干扰（EMI）的增加。屏蔽方法是减少隔离变压器内部耦合的最有效方法。而夹层绕组变压器的箔屏蔽设计很少涉及，以抑制反激式转换器中的CM EMI。在这项工作中，我们提出了一种方法来确定初级 - 次级 - 初级夹层绕组变压器中双层箔屏蔽的最佳宽度，以最小化反激转换器的传导 CM EMI。分析等电位分布和结构电容，建立等效共模电容模型，计算流过夹心绕组变压器的最小共模电流。通过计算和测量结果的比较验证了所提出的方法。