APWM Resonant Converter with SST for EMI Filter Size Reduction

A spread spectrum technique (SST) has been introduced to alleviate electromagnetic interference problem in switch mode power converters. Previously, the SST was employed to low power and small size power converters, such as buck converter, because these converter has insensitive voltage gain by the switching frequency variations. However, the resonant converters are hard to apply the spread spectrum technique, because the resonant converter has a sensitive voltage gain according to the variation of switching frequency. This paper proposes a resonant converter using the asymmetric pulse width modulation and the spread spectrum technique is developed for 100 W off-line power supply applications. The design methodology of the power stage is analyzed to regulate the output voltage tightly. The input EMI filter is analyzed to reduce the filter size with and without the spread spectrum technique. The output voltage regulation and the reduction of EMI filter size are analyzed and experimentally verified with a 100 W prototype converter.