Fundamental limits on energy transfer and circuit considerations for piezoelectric transformers

This work investigates fundamental limits on the electromechanical energy conversion capacity of piezoelectric transformers by considering a work cycle analysis. Fundamental limitations are imposed by maximum electric field strength, maximum surface charge density, maximum stress and maximum strain. The authors´ analysis indicates that the mechanical stress limit is the effective constraint in typical PZT materials. For a specific PZT-5H sample considered, a mechanical stress-limited work cycle indicates that this material can handle 330 W/cm³ at 100 kHz. The theory of operation of soft-switching resonant drive circuitry is then discussed. Experimental results on a soft-switching inverter incorporating no magnetic components are reported