EMI Analysis and Suppression Method Using Ferrite Beads Applied to LLC Converter

To operate the LLC converter at high switching frequency, the excitation current flowing through the transformer is increased, which generates a large conducted noise. The peaks in the noise spectrum are caused by the ringing of the switching node voltage and the resonance of the CM equivalent circuit. In this paper, a method using ferrite beads and additional resistors in combination with the input filter is proposed to suppress the ringing. Its effectiveness in reducing the high-frequency noise while maintaining the fast-switching speed is confirmed by simulation and experiment.