Tunable high-power multilayer piezoelectric transformer

Piezoelectric transformers (PTs) have been conventionally used in step-up high-voltage low-power applications such as liquid crystal display (LCD) backlighting for portable electronic devices. PTs have also been considered for step-down applications such as battery chargers for portable devices. In these applications, adapting the output impedance of the PT to meet the requirements of lower output voltages and higher output currents implies the design of PTs with larger number of output layers. Furthermore, these step-down applications require efficient operation of PT under a variety of output load conditions to meet the conditions of battery charging. Thus, strategies to adapt the PT to the variation of the output load are being pursued. In this article, a novel tunable piezoelectric transformer (TPT) for ac-dc and dc-dc high-power converters is presented. This TPT is designed to operate in the radial mode and is fabricated using cofired multilayer process. By introducing control layers into the design, the TPT is shown to provide desired features that include adjustable frequency response and flexible transfer ratio. Fabricated TPT exhibits high efficiency over 96% with an output power capability of 40 W when operating under its nominal load conditions.