Piezoelectric transformer, piezoelectric transformer unit, inverter circuit, light emission control device, and liquid crystal display device

Abstract

A low loss, small scale piezoelectric transformer, suited for a cold cathode tube load, and having a high effective coupling factor, is provided using a piezoelectric plate having a single polarization direction. Controlling the dimensions of the third electrode portionconstituting the high impedance portion makes it possible easily to adjust the capacitance of the electrostatic capacitor formed between the first electrode portionand the third electrode portion in accordance with the load. Also, the second electrode portionand the fourth electrode portionconstituting the low impedance portion are substantially equal in area and the third electrode portion and the fourth electrode portion are formed in one piece, so that energy propagation efficiency can be increased. Consequently, the effective coupling factor resulting from the electrode structure and the vibration mode can be kept high even if the capacitance is changed freely, and thus high element efficiency and a small amount of generated heat can be maintained and stress can be decreased.