Analysis and Design of EMI Filter Based on Differential Mode Inductor Magnetic Integration

Traditionally, the leakage inductance of the common-mode suppressor coil is used as the differential mode inductance. However, in the circuit topology with high differential mode noise, a separate differential mode filter is often needed, which results in a large volume of magnetic parts. When the common-mode noise of the optimized transformer is relatively tiny, differential mode inductance can be used to replace the common-mode suppression coil with a large sense. The same effect of common mode noise suppression is achieved by using the common-mode suppression coil with a small sense value. At the same time, insertion loss can represent the effect of noise suppression. On this basis, an EMI filter with integrated magnetic structure based on decoupled differential mode filter inductor is proposed. Compared with the original scheme, the volume of magnetic components in the EMI filter is reduced by 40% under the premise of keeping the same noise suppression effect, and the effect is obvious. In this paper, a PFC+QR flyback power supply is used to test the filter insertion loss and the noise of the whole machine. Finally, the feasibility of this scheme is verified by comparing the initial and integrated prototypes.