Analysis of Inductorless Zero-Voltage-Switching Piezoelectric Transformer-Based Converters

The inductorless piezoelectric transformer (PT)-based resonant converter topology allows all the components between the half-bridge inverter and rectifier in a conventional LCC converter to be replaced with a single ceramic component. This offers potential savings in cost, size, and mass. However, zero-voltage switching (ZVS) becomes more difficult to achieve because the MOSFET output capacitances are augmented by the PT input capacitance. This paper presents an analytical model for the ZVS condition in inductorless PT-based converters. Unlike previously reported models, the proposed model is shown to offer a level of accuracy comparable to a SPICE simulation and to correlate well with experimental results. Using a normalization scheme and numerical optimization techniques, the criteria for achieving inductorless ZVS are found in terms of the equivalent circuit components. Both ac-output and dc-output variants are considered, and design charts for ensuring ZVS in five different topologies are presented. The results and design charts are applicable to any type of PT that can be represented by the standard PT equivalent circuit.