Empiric analysis of zero voltage switching in piezoelectric transformer based resonant converters

Research and development within piezoelectric transformer (PT) based converters are rapidly increasing, as the technology is maturing and starts to prove its capabilities. High power density and high efficiencies are reported and recently several inductor-less converters have emerged [1][2][7][10][13], which demonstrates soft switching capabilities. The elimination of a bulky inductor, reduces size and price of the converter, but demands a soft switching optimised PT. Several attempts of expressing the soft switching capability have been made [5][12], with some shortcomings. The goal of this paper is to derive a simple expression of the maximal obtainable soft switching capability (ZVS factor), for a specific PT design, assuming a matched load. The expression has been derived through series of parametric sweep simulations of the inductor-less half- bridge topology, which revealed that a linearization of the maximal soft switching capability can be performed, in the area of interest. This expression is intended to form a basic tool for development of soft switching optimised PT´s, which enables the utilisation of inductor-less topologies.