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 portion 15 a constituting the high impedance portion makes it possible easily to adjust the capacitance of the electrostatic capacitor formed between the first electrode portion 12 and the third electrode portion in accordance with the load. Also, the second electrode portion 13 and the fourth electrode portion 15 b constituting 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.

1 - 21 . (canceled)  
   
   
       22 . A method of making 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; 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 portion and the fourth electrode portion;    the method comprising:    forming a high impedance portion with the first electrode portion and the third electrode portion in the thickness direction of the piezoelectric plate, and a low impedance portion with the second electrode portion and the fourth electrode portion in the thickness direction of the piezoelectric plate, and    adjusting a capacitance of an electrostatic capacitor formed between the first electrode portion and the third electrode portion in accordance with the load by changing the dimensions of the third electrode portion, so as to adjust an area of the third electrode portion overlapping with the first electrode portion in the thickness direction of the piezoelectric plate.    
   
   
       23 . The method of making a piezoelectric transformer according to  claim 22 , wherein the piezoelectric plate is in the shape of a circular disk.  
   
   
       24 . The method of making a piezoelectric transformer according to  claim 22 , wherein the piezoelectric plate is in the shape of a rectangular plate substantially equal in length and width.  
   
   
       25 . A method of making a piezoelectric transformer comprising: 
 a piezoelectric plate polarized entirely in a thickness direction and shaped as a rectangular plate substantially equal in length and width;    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 to the interior of a first insulating region provided at a perimeter portion of the first principal face, and separated from the first electrode portion by a second 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 having an area substantially equal to that of the first electrode portion; and    a fourth electrode portion formed integrally with the third electrode portion on the second principal face and extending from the third electrode portion to the perimeter portion along center lines of the four edges with third insulating regions being provided at four corner areas of the second principal face;    the method comprising;    forming a low impedance portion with the first electrode portion and the third electrode portion in the thickness direction of the piezoelectric plate, and a high impedance portion with the second electrode portion and the fourth electrode portion in the thickness direction of the piezoelectric plate, and    adjusting a capacitance of an electrostatic capacitor formed between the fourth electrode portion and the second electrode portion in accordance with the load by changing the dimensions of the fourth electrode portion, so as to adjust an area of the fourth electrode portion overlapping with the second electrode portion in the thickness direction of the piezoelectric plate.    
   
   
       26 . The method of making a piezoelectric transformer according to  claim 25 , wherein the first electrode portion is geometrically similar to the outer dimensions of the piezoelectric plate.  
   
   
       27 . A method of making a piezoelectric transformer comprising: 
 a piezoelectric plate polarized entirely in a thickness direction and shaped as a rectangular plate substantially equal in length and width;    a first electrode portion formed in linear symmetry about the diagonals on a first principal face in the thickness direction of the piezoelectric plate;    a second electrode portion formed in a middle portion of each of four perimeter portions on the first principal face, and separated from the first electrode portion by a second 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 having a shape substantially corresponding to that of the first electrode portion; and    a fourth electrode portion formed integrally with the third electrode portion on the second principal face and extending from the third electrode portion to the perimeter portions along the center lines of the four edges with insulating regions being provided at areas between a periphery of the third electrode portion and a periphery of the fourth electrode portion;    the method comprising:    forming a low impedance portion with the first electrode portion and the third electrode portion in the thickness direction of the piezoelectric plate, and a high impedance portion with the second electrode portion and the fourth electrode portion in the thickness direction of the piezoelectric plate, and    adjusting a capacitance of an electrostatic capacitor formed between the fourth electrode portion and the second electrode portion in accordance with the load by changing the dimensions of the fourth electrode portion, so as to adjust an area of the fourth electrode portion overlapping with the second electrode portion in the thickness direction of the piezoelectric plate.