EMI Noise Reduction and Output Ripple Cancellation for FullWave Type SoftSwitching Converter This paper proposes a novel EMI noise reduction technology with fullwave type softswitching converter. Using resonance to realize the ZeroVoltage Switching (ZVS) operation, a softswitching converter can realize high efficiency and low EMI noise. However, unnecessary radiation and conduction noises of the input current by the switch are still large. This kind of converter has an operating frequency dependent on the resonant waveform. Since the fixed frequency clock is not used, the frequency modulation of the PWM operation signal is strict and the EMI reduction is difficult. In this paper, we show that in the fullwave type resonant softswitching converter, by modulating the time shift of the resonance end edge, the spectrum of EMI and conduction noises are reduced. At this time, modulation of the resonant operation adversely affects the ZVS operation, and the output ripple also increases. Along with this ripple cancellation circuit, the ZVS operation is also improved to reduce the EMI spectrum by more than 10dB. Furthermore, the output modulation ripple can be suppressed to 1mV.

Output Voltage Ripple Reduction with Nosie Spread Spectrum for DualPhase 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 dualphase LLC resonant converter, where the output voltage ripple increase is suppressed by the frequency modulation so as to cancel the ripples with each other.