Design of the Number of Transformer Shielding Winding Turns for Minimizing Low-Frequency Common-Mode Noise in Flyback Converters

Transformer shielding techniques are widely applied to suppress common-mode (CM) noise. As an important shielding method, winding shielding gains lots of attention because of its convenience and cost effectiveness. For suppressing CM noise effectively, the number of shielding winding turns should be carefully decided. This paper proposes a design method of the number of transformer shielding winding turns for minimizing low-frequency CM noise in flyback converters. This is realized through exploring the relation between low-frequency CM current and the number of shielding winding turns. With this method, the optimal number of shielding winding turns can be obtained without calculation and comparison of CM currents in converters with different shielding winding turns. By comparing CM noise measurement results, the proposed method is validated. The proposed method can be a guideline on the design of transformer shielding winding.