Piezoelectric transformer for 30 W output AC-DC converters

A piezoelectric transformer using AC-DC converters is described that has a multilayered construction in the thickness direction and operates in contour-extensional vibration mode. The output impedance is designed to be low - approximately several tens of ohms. Testing of a fabricated transformer 14 mm long, 14 mm, wide, and 5.8 mm showed that it had a 0.4 gain, 26 W output power, and 96.3% efficiency at 135 kHz when the temperature increase was 30/spl deg/C. A fabricated AC-DC converter with this transformer had good line and load regulation and a maximum efficiency of 90.2%.