Output Voltage Increase of a Series Resonant DC-DC Converter

It has been considered that the series resonant converter takes the maximums of the output voltage in the resonant frequency. However, in practice, the series resonant converter takes the maximums of the output voltage that appears in the lower frequency band compared with the resonant frequency. We analyzed the output voltage characteristics of a series resonant converter circuit when the switching frequency is lower than the resonant frequency including the transformer magnetizing inductance from a transformer. As a result, it was confirmed that for the series resonant converter, the output voltage takes maximum at a lower frequency than the resonant frequency, and the output voltage is larger than the input voltage; that is, the converter has the output boost characteristics, and consequently, this converter can be used when the input voltage is varied widely. In addition, the switching frequency is clarified when the output voltage takes the maximum according to the load resistance and magnetizing inductance.