New Tunable Piezoelectric Transformers and Their Application in DC–DC Converters

This paper introduces a new tunable piezoelectric transformer (TPT) and demonstrates its operation in a dc–dc converter application. Piezoelectric transformers (PTs) have been conventionally used in high-voltage, low-power applications such as electronic ballasts. Recently, radial type PTs have been developed for higher power ac–dc and dc–dc step down applications. Based on the latter, a new TPT has been developed featuring an auxiliary secondary terminal to control the voltage gain of the transformer. This results in some exciting characteristics from a dc–dc converter standpoint, like an adjustable frequency response of the TPT, and fixed frequency control of the converter with no-cross talk between the primary and secondary in the control circuit. This paper introduces the design concept behind TPT-based dc–dc converters, and proposes a control scheme for their implementation. Experimental results with a 30 W, 220:55 V converter unit are shown to validate these concepts.