Design and implementation of a converter with wide operating range using a Variable-Inverter-Rectifier-Transformer structure

Abstract

Power supplies for portable electronics such as cell phones, tablets, and laptops characterized by the low-voltage load are supplied by a single-phase grid-tied ac-dc converter. Achieving miniaturization and high efficiency of power supplies in this application is challenging due to the large voltage conversion ratios and the large variations in conversion ratios. The fact that low-output-voltage, large step-down transformers are often constrained by a minimum single-turn secondary also exacerbates loss and size constraints in such applications. To address this, a new hybrid magnetic-electronic structure is explored - the Variable-Inverter-Rectifier-Transformer (VIRT). This new approach enables voltage conversion in which the transformer provides fractional and reconfigurable effective turns. This new VIRT approach is developed, and multiple implementation approaches are explored, designed and implemented. This design is further augmented with a rectifier topology which allows for a full utilization of the effective core area in all modes of operation and hence improvement in a core loss. Moreover, a hybrid Litz-PCB construction of VIRT transformer is explored. This approach reduces copper loss and easily satisfies the voltage insulation requirements in such "off-line" applications (2.5 kV in this case [1]) through use of a triple insulated litz wire.