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

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.