Patent ID: 7030538

Claim:
A piezoelectric transformer, comprising: a piezoelectric plate polarized entirely in a thickness direction; a first electrode portion formed in a center portion on a first principal face in the thickness direction of the piezoelectric plate; a second electrode portion enclosing the first electrode portion and formed from an interior to an edge on the first principal face, and separated from the first electrode portion by an insulating region; a third electrode portion formed on a second principal face in the thickness direction of the piezoelectric plate in a region in opposition to the first electrode portion and the insulating region and facing the first electrode portion with an area smaller than a whole area of the first electrode portion, so as to be suitable for adjusting a capacitance of an electrostatic capacitor formed between the third electrode portion and the first electrode portion; and a fourth electrode portion formed integrally with the third electrode portion on the second principal face and having an area substantially equal to that of the second electrode portion, with an insulating region being provided partially between the third electrode and the fourth electrode portion; wherein a high impedance portion is made of a portion formed by the first electrode portion and the third electrode portion in the thickness direction of the piezoelectric plate, and a low impedance portion is made of a portion formed by the second electrode portion and the fourth electrode portion in the thickness direction of the piezoelectric plate, and the high impedance portion is suitable for adjustment of the impedance in accordance with a load by adjusting a dimension of the third electrode portion.