Novel techniques to reduce common-mode (CM) and mix-mode (MM) EMI noise emissions based on noise balance and cancellation

In an input-offline switched-mode power supply (SMPS) system, especially in comparison with the cost of noise reduction, significant EMI improvements can be made by incorporating the additional windings, dV/dt balancing winding (B-Winding) and core cancellation winding (C-Winding) into a transformer. However, it is unclear how these additional windings work. In this paper, analytical techniques and explanations of noise current balancing and cancellation mechanisms of such windings are given. As a result, the B- and C-Windings can be integrated into a single transformer to improve both DM (by reducing the mix-mode (MM) EMI noise) and CM EMI performances without any conflicts and compromises. Design examples are given and experiments are finally carried out to verify the proposed theory.