Output Voltage Ripple Reduction with Nosie Spread Spectrum for Dual-Phase LLC Resonant Converter

In recent years, the restriction of Electro Magnetic Interference (EMI) due to switching noise of a switching power supply becomes more severe, and there are many regulations worldwide. In this paper, we propose a method to spread the noise spectrum by modulating the switching frequency to reduce the EMI noise in the LLC resonant converter. The LLC resonant converter is used to adjust the output voltage by controlling the switching frequency. However, its EMI noise reduction by the frequency modulation increases the output voltage ripple. Then we propose a dual-phase LLC resonant converter, where the output voltage ripple increase is suppressed by the frequency modulation so as to cancel the ripples with each other.