Radiated EMI Reduction with Double Shielding Techniques in Active-Clamp Flyback Converters

Electromagnetic interference (EMI) issue becomes a headache problem when the switching frequency has been pushed higher and higher for the smaller size and higher power density. Up to now, the conducted EMI can be controlled very well with decades of exploration and research. However, the radiated EMI is still hard to be understood and controlled, the techniques to reduce the radiated EMI are limited. In this paper, active-clamp flyback converters are taken as the example, the radiation model is developed, the double shielding technique is proposed to mitigate the radiated EMI effectively no matter the EMI filters are placed on the AC line or DC bus. The concept of this technique is explained in detail, the experiments are conducted to verify the analysis. The guideline to choose the appropriate connection method of the double shielding technique is given for both the AC line and DC bus EMI filters.