Patent ID: 6989626

Claim:
A piezoelectric transformer comprising: a rectangular plate made of a piezoelectric material; and primary electrodes and secondary electrodes each formed on said rectangular plate; wherein said primary electrodes comprise a first electrode pair formed in a central portion in the longitudinal direction of said rectangular plate, and a second electrode pair and a third electrode pair formed adjacent to said first electrode pair and on one side and on the other side of said first electrode pair in the longitudinal direction of said rectangular plate, respectively; two electrodes of one of said first, second and third electrode pairs are formed opposed each other on two main surfaces of said rectangular plate perpendicular to a thickness direction of said rectangular plate to interpose said rectangular plate therebetween; said first, second and third electrode pairs are formed symmetrically with respect to a center line perpendicular to the longitudinal direction of said rectangular plate and dividing said rectangular plate in half in the longitudinal direction of said rectangular plate; an area of each electrode of said second and third electrode pairs is smaller than an area of each electrode of said first electrode pair; a length of each electrode of said second and third electrode pairs is equal to that of each electrode of said first electrode pair in the width direction of said rectangular plate; a length of each electrode of said second and third electrode pairs is not less than 10% and shorter than 100% of the length of each electrode of said first electrode pair in the longitudinal direction of said rectangular plate; and said secondary electrodes comprise a plurality of electrodes formed near the two ends of said rectangular plate in the longitudinal direction of said rectangular plate; whereby a voltage is output from said secondary electrodes when an alternating voltage is applied to said primary electrodes to excite mechanical vibrations of a 3/2 wavelength to expand and contract said rectangular plate in a longitudinal direction thereof in said rectangular plate.