EMI Reduction by Spread Spectrum Clocking with Ripple Suppression for LLC Resonant Converter

This paper describes an EMI noise reduction technique with suppression of the output ripple increase by applying a spectrum spread clocking method on an LLC resonant converter. The LLC resonant converter is a PFM control switching converter without an external clock and direct application of clock frequency modulation for spectrum spread is difficult, and hence for its realization, some circuits are designed. However, this method increases the output ripple if there is any care, and hence we propose its two measures; (i) the duty ratio compensation where the switching pulse duty ratio is modulated according to the modulation of the switching frequency and (ii) the dead time compensation where the switching pulse dead time is changed according to the frequency modulation. Our simulation results show their effectiveness.