PFC+半桥LLC电路传导共模EMI特性分析与抑制

为了研究开关电源的传导共模EMI特性，在分析交错并联PFC+半桥LLC电路传导共模噪声传输机理基础上，提出了磁元件可视为共模滤波器的新观点。理论分析了磁元件的共模滤波特性，通过优化设计变压器绕组结构，改善变压器容性分布特性，可提高变压器的共模噪声滤波能力；通过构造反相噪声源，补偿抵消原始噪声，可提高功率电感共模噪声滤波能力。最后，通过一台音频功放电源样机进行了实验验证，实验结果表明优化磁元件共模EMI滤波特性，可有效抑制电路的共模噪声。

Analysis and suppression of conducted common mode EMI characteristics of PFC+half-bridge LLC circuit

In order to study the characteristics of conducted common mode(CM) EMI of Switched Mode Power Supply, based on the analysis of CM noise transmission mechanism of interleaved parallel PFC and half-bridge LLC circuit, a new viewpoint that magnetic elements can be regarded as CM filter is proposed. This paper analyzes the characteristics of CM filtering of magnetic elements theoretically. By optimizing the winding structure of the transformer and improving the capacitive distribution characteristics of the transformer, the CM noise filtering ability of the transformer can be improved; By constructing inverse noise sources to compensate and cancel original noise, the CM noise filtering ability of the power inductor can be improved. Finally, experimental verification is conducted with an audio amplifier power supply prototype. The results show that optimizing the CM EMI filtering characteristics of magnetic elements can effectively suppress the CM noise of the circuit.