Design of a circular piezoelectric transformer with crescent-shaped input electrodes

In this study, a new disk-type piezoelectric transformer design is proposed. The input side of the transformer has a crescent-shaped electrode and the output side has a focused poling direction. The electrodes and poling directions on commercially available piezoelectric ceramic disks were designed so that the planar or shear mode coupling factor (k_p or k₁₅) becomes effective rather than the transverse mode coupling factor (k₃₁). ATILA finite element code was used to analyze transformer behavior and to optimize electrode and poling configurations. The voltage step-up ratio of the proposed transformer has been markedly improved in comparison with that of the equivalent rectangular type. A single layer prototype transformer, 25.4 mm in diameter and 1.0 mm thick, operated at 92.8 kHz, was fabricated and its characteristics, such as step-up ratio and power transformation efficiency were measured. While the transformer was driving a cold cathode fluorescent lamp (CCFL), the temperature field of the transformer was also observed.