Abstract
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.
Published Version
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