Tightly Regulated Current- Fed LLC Resonant Converter Employing Spread Spectrum Technique to Reduce Electromagnetic Interference

A spread spectrum technique (SST) can effectively reduce the conductive noise by spreading the operating frequency without additional components. However, the input-output voltage gain of the resonant converter is highly sensitive to the operating frequency, it is hard to apply the SST to the resonant converter. In this paper, the SST is employed to a current-fed LLC resonant converter with low output voltage ripple. The resonant network design is provided to obtain the insensitive voltage gain according to the operating frequency, which can reduce the output voltage ripple caused by the SST operation. The proposed current-fed LLC resonant converter with the SST is implemented to a 200-W prototype, and its performance is be evaluated in terms of the output voltage ripple and the EMI reduction by experiments.