Optimization of an Unregulated Low-Q Resonant Isolated DC-DC Stage for Low-Power AC-AC Converters

Low-power line-frequency transformers are common across several applications, but these transformers are found to have large standby losses, low efficiencies, large weights, and high costs. In this paper we optimize a power conversion stage for this and other applications where an unregulated, isolated converter is needed. The selected topology uses low-impedance passives to reduce their size; to address this case we analyze operation of a lower-Q resonant tank. Lastly, because of the application of low-power line-frequency transformers, we optimize around a typical usage cycle to minimize the yearly average power loss. For the application of a Class 2 line-frequency transformer, model results are accurate to simulation by within 12.1%, and optimization produced a design that was experimentally validated to achieve a yearly average power loss of 285.1 mW, a peak efficiency of 99.26% and a standby loss of 155 mW.