Unipoled disk-type piezoelectric transformers

Unipoled piezoelectric transformers with different input and output area ratios were fabricated. The electrical properties in terms of voltage step-up ratio, output power, efficiency, and temperature rise were measured at various load resistance. The voltage step-up ratio increased proportionally with load resistance. The relative efficiency showed a maximum value of more than 98% in the transformer, which is 23.6 mm in diameter and 1.0 mm in thickness with input/out electrode area ratio of 0.62. With the driving voltage of 35 V-rms, the 8.1 W output power was obtained in the transformer with an input/output electrodes area ratio of 6.47. In such conditions, the temperature rise was only 15degreesC front room temperature. This transformer, which has approximately ten times higher power density than a rectangular Rosen-type piezoelectric transformer, was successfully applied to operate an 8 W compact fluorescent lamp.