High frequency zero voltage switched off-line power converters

The zero voltage switched multi-resonant converter (ZVSMRC) in which all the semiconductor devices are switched under volt-free conditions, and the series-parallel loaded resonant converter (SPRC) are studied and compared. It is found that the MRC overcomes the minimum load restriction of the simple ZVSQRC achieving ZVS under all load and line conditions. It is also capable of achieving the highest conversion efficiency of the circuits studied due to its relatively low RMS currents and zero diode snubbing losses. However it does this at the expense of a very wide control frequency range; great care must be taken to ensure that the converter cannot operate in MODE II, or closed loop operation becomes impossible. Furthermore the MRC does not seem to be readily adaptable for additional outputs. The SPRC overcomes the part-load efficiency problem of the PRC, by reducing the resonant current amplitude, at the expense of a wider control frequency range. Design of the converter is simple and multiple output operation is possible. However, rectifier diode snubbing may be necessary in some instances and efficiency is not as high as for the MRC