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EMI Noise Reduction and Output Ripple Cancellation for Full-Wave Type Soft-Switching Converter

This paper proposes a novel EMI noise reduction technology with full-wave type soft-switching converter. Using resonance to realize the Zero-Voltage Switching (ZVS) operation, a soft-switching 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 full-wave type resonant soft-switching 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.