Comparative assessment of zero voltage switched off-line power convertor topologies

Four half-bridge zero voltage switched (ZVS) convertor topologies are compared for offline applications in the 100–200 W range at a full-load switching frequency of 1 MHz. First, the quasi-resonant convertor (QRC) and the parallel-loaded resonant convertor (PRC) are studied. A review of the theory of circuit operation is followed by design procedures and experimental results which indicate that neither circuit provides satisfactory performance. Hence the multiresonant convertor (MRC) and series parallel-loaded resonant convertor (SPRC), which are derived from the previous topologies, are considered. Again, theoretical operation is reviewed, design procedures evolved and experimental results presented and discussed. The possibilities for increasing switching frequency are investigated for each topology and technological bottlenecks are identified. Both circuits are shown to be suitable for these applications, the MRC providing higher efficiency at the cost of wider control frequency range and poorer repeatability.