Interaction of CM Noise Paths Between the Flyback Auxiliary Power Supply and the Main Circuit and Low-Noise Configuration Design

Abstract

The flyback converter is widely employed as auxiliary power supplies in power electronic systems. However, in such configurations, bidirectional common-mode (CM) noise interaction exists between the auxiliary power supply and the main circuit, leading to severe electromagnetic interference (EMI) issues. To address this problem, a system-level CM noise conduction equivalent model incorporating the auxiliary power supply is established, and the corresponding noise coupling mechanisms are thoroughly analyzed. Based on this model, a low-noise configuration optimization method is proposed. By identifying the critical noise propagation paths, the drive power supply configuration of the auxiliary converter is optimized, thereby increasing the CM impedance along key paths and suppressing interference through noise cancellation principles. Experimental results demonstrate that, without introducing additional filtering components, the proposed method reduces the CM noise generated by the auxiliary power supply by more than 20 dB $\mu $ V while effectively suppressing the noise originating from the main circuit.