Transformer balancing winding technology with effective shielding for suppressing common mode noise in flyback converters

Abstract

The main methods for suppressing the common mode (CM) noise in flyback converters include adding a shielding layer and adding a balancing winding. To combine the advantages of both methods, a balancing winding with a shielding effect is proposed to suppress CM noise. First, the CM noise transmission path of a flyback converter is analyzed, and an equivalent model of CM noise is established. Then, combined with the CM noise characteristics of the flyback converter, the design criteria for the shielding-balancing winding are given. Finally, experiments are conducted on a flyback converter prototype. The CM noise spectra of four transformer structures (without a shielding layer, with a traditional copper foil shielding layer added, with a balancing winding and with the proposed shielding-balancing winding) are compared. The results show that the CM noise of the flyback converter can be effectively suppressed by adding the shielding-balancing winding proposed in this paper. In addition, the effectiveness of the proposed method is verified.