Abstract:
There is provided with a piezoelectric transformer which does not require a marking operation, is easy to manufacture, and is capable of reducing costs. After the piezoelectric transformer is manufactured, a shape of secondary side electrodes on the outer end is made so that a polarization direction can be recognized at the time of printing the secondary side electrodes without marking by a separate step to recognize the polarity on the primary side.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a piezoelectric transformer using a piezoelectric ceramics as an element for generating high voltage, and as an element for converting voltage.  
         [0003]     2. Description of the Related Art  
         [0004]     A piezoelectric transformer using a piezoelectric ceramics is widely used for a light source for a backlight which illuminates from a rear side a liquid crystal used in a personal computer and the like, used for a DC/DC converter of a power supply, and for a high-voltage power source of an air cleaner and the like. This kind of piezoelectric transformer is obtained by providing primary and secondary electrodes to a piezoelectric ceramics such as PZT, and polarizing it by applying a high electric field to the respective electrodes to align crystal axes.  
         [0005]     Conventionally, in a general piezoelectric transformer, as shown in  FIG. 6 , primary side electrodes  3 ′ are provided by printing on the top and bottom surfaces of one half of an elongated piezoelectric ceramics  2 ′ having a rectangular shape viewed from the upper side, and secondary side electrodes  4 ′ having a rectangular shape are similarly provided by printing at the outer ends of the top and bottom surfaces in the other half.  
         [0006]     In this piezoelectric ceramics  2 ′, a generating part between the primary side electrodes  3 ′ is polarized, for example, in a direction shown by an arrow a, and an output part side at the other half part is polarized, for example, in a direction shown by an arrow b. A piezoelectric transformer  1 ′ is configured by such polarizations.  
         [0007]     In the piezoelectric transformer  1 ′, when a voltage with a unique resonant frequency decided by a longitudinal direction of the primary side of the transformer is applied, elements are vibrated by counter-piezoelectric effect, and a positive or negative voltage corresponding to the vibrations can be picked up from the secondary side by piezoelectric effect. The characteristics of the transformer can be changed by changing a polarization direction.  
       SUMMARY OF THE INVENTION  
       [0008]     Conventionally, there is a problem that, to indicate a polarization direction a on a generating part side, a marking with a suitable shape is applied to the piezoelectric transformer  1 ′ at predetermined positions in a separate marking step, which leads to that manufacture is complicated and costs become increased.  
         [0009]     The present invention is made in view of the above-mentioned problem, and an object of the present invention is to provide a piezoelectric transformer which does not require a marking operation, is easy to manufacture, and is capable of reducing costs.  
         [0010]     In the invention described in claim  1 , a secondary side electrode provided at an end of at least one face of a piezoelectric ceramics is formed into a shape for indicating a polarity.  
         [0011]     The invention described in claim  2  is the piezoelectric transformer described in claim  1 , wherein an inner shape of the secondary side electrode is a linear shape extending substantially in a width direction of the piezoelectric ceramics, and an outer shape of the secondary side electrode is a polarity-recognizable shape which is different from the linear inner shape.  
         [0012]     According to the inventions described in claims  1  and  2 , the polarity on the primary side of the piezoelectric ceramics can be known by the electrode shape on the secondary side, so that there is no need for adding a separate step to apply markings, and therefore the transformer can be manufactured more easily.  
         [0013]     Also, since the secondary side electrode can be easily provided by one printing, costs can be reduced. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1A  is a perspective view of a piezoelectric transformer in a first embodiment of the present invention, and  FIG. 1B  is a diagram for explaining advantages of the present invention;  
         [0015]      FIG. 2  is a perspective view of the piezoelectric transformer in a second embodiment of the present invention;  
         [0016]      FIG. 3  is a perspective view of the piezoelectric transformer in a third embodiment of the present invention;  
         [0017]      FIG. 4  is a perspective view of the piezoelectric transformer in a fourth embodiment of the present invention;  
         [0018]      FIG. 5  is a plane view of the piezoelectric transformer in a fifth embodiment of the present invention; and  
         [0019]      FIG. 6  shows a conventional piezoelectric transformer. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     Now, embodiments of the present invention will be explained with reference to the drawings.  
       Embodiment 1  
       [0021]      FIG. 1  is a perspective view of a piezoelectric transformer in a first embodiment of the present invention.  
         [0022]     In this piezoelectric transformer  1 , primary side electrodes  3  are provided on the top and bottom surfaces of a piezoelectric ceramics  2  on a generating part side by printing, respectively.  
         [0023]     Also, secondary side electrodes  4  are provided by printing at the ends of the top and bottom surfaces of the piezoelectric ceramics  2  on an output part side. In this embodiment, at least one secondary side electrode  4  has a substantially triangular shape  
         [0024]     The generating part between the primary side electrodes  3  on the top and bottom surfaces is polarized, for example, in a direction of the arrow a, and the output part is polarized in a direction of the arrows b.  
         [0025]     According to the present invention, the polarization direction a between the primary side electrodes  3  is made recognizable by printing the substantially triangular secondary side electrode  4 , for example, with its peak  4   a  directed to the outside of the piezoelectric ceramics  2  and printed, so that . That is to say, the polarity on the primary side of the piezoelectric ceramics  2  is made recognizable. Accordingly, there is no need to apply markings by a separate step as in prior art.  
         [0026]     In here, it is not preferable to make the secondary side electrode  4  in a trapezoidal shape with its shorter side facing the inside and the longer side facing the outside as shown in  FIG. 1B , because it makes the polarization conditions on the surface side and the inside in the output part not uniform.  
         [0027]     Meanwhile, as shown in  FIG. 1A , when the secondary side electrode is formed into an approximately triangle shape, and the peak  4   a  is directed to the outside and the linear longer side  4   b  extending substantially in the width direction of the piezoelectric ceramics  2  is facing the inside, polarity on the output part side is not changed from the conventional one shown in  FIG. 6 , and it is possible to make the piezoelectric transformer have same characteristics.  
         [0028]     Also, the secondary side electrodes  4  are not limited to the shape shown in  FIG. 1A , and may have any other shape that the polarization direction a of the generating part is recognizable, i.e., that the polarity on the primary side of the piezoelectric ceramics  2  is recognizable.  
       Embodiment 2  
       [0029]      FIG. 2  shows a second embodiment of the present invention. In this embodiment, secondary side electrodes  4 A are formed into an approximately trapezoidal shape, while bottom bases  4   b ′ linearly extending along a width direction of the piezoelectric ceramics  2  are directed to the inside and top bases  4   a ′ shorter than the bottom bases  4   b ′ are directed to the outside.  
         [0030]     In this manner, the inner ends of the secondary side electrodes  4 ,  4 A are formed into a shape linearly extending along an approximately width direction of the piezoelectric ceramics  2 , and outer ends are formed into a different and suitable shape, so that the polarization direction can be recognized by the shape of the outer end.  
       Embodiment 3  
       [0031]      FIG. 3  shows a third embodiment of the present invention. In this embodiment, a secondary side electrode  5  on the top surface is formed into an arc shape surrounded by an arc  5 A which is a part of a circle or a semicircle, and a chord  5 B. That is to say, in the secondary side electrode  5 , the chord  5 B linearly extending along the width direction of the piezoelectric ceramics  2  is directed to the inside and the arc  5 A is directed to the outside relative to the chord  5 B.  
         [0032]     In Embodiment 3, the polarity on the primary side of the piezoelectric ceramics  2  can be recognized by an arc shape of the secondary side electrode  5  on the top surface.  
       Embodiment 4  
       [0033]      FIG. 4  shows a fourth embodiment of the present invention. In this embodiment, a secondary side electrode  6  on the top surface is formed into an oval arc shape surrounded by an oval arc  6 A which is a part of an oval or a semi-oval, and a chord  6 B. That is to say, in the secondary side electrode  6 , the chord  6 B linearly extending along the width direction of the piezoelectric ceramics  2  is directed to the inside, and the oval arc  6 A is directed to the outside relative to the chord  6 B.  
         [0034]     In Embodiment 4, the polarity on the primary side of the piezoelectric ceramics  2  can be recognized by an oval arc shape of the secondary side electrode  6  on the top surface.  
       Embodiment 5  
       [0035]     In Embodiment 5, as shown in  FIG. 5 , when a lead wire  11  is connected with the secondary side electrode  4  of Embodiment 1 by a solder  12 , the solder  12  is applied to a portion surrounded by three sides of the approximately triangular secondary side electrode  4 , so that a volume of the solder  12  can be adjusted by the shape of the secondary side electrode  4 . Thereby, poor vibrations generated by increasing the volume of the solder  12  can be reduced. In the case of applying the solder in Embodiments 2 to 4, the volume of the solder can be similarly adjusted by the shape of the secondary side electrode.  
         [0036]     Embodiments 1 to 5 are described as above. In these embodiments, the secondary side electrode on the bottom surface has a square shape or a shape different from that of the secondary side electrode on the top surface.  
         [0037]     Also, the present invention is not limited to the above-mentioned embodiments, and various changes can be made to the invention without departing from the sprit of the present invention. That is to say, a slit (not shown) may be formed, for example, on the secondary side electrode on the top surface on the inner sides of the secondary side electrodes  4 ,  4 A, namely on the primary side electrode  3  side, so that the polarity can be recognized by existence of the slit. In this case, the solder is not applied on the slit portion, so that the volume of the solder can be adjusted. Accordingly, loads on the secondary side electrodes  4 ,  4 A side can be reduced, so as to prevent breakage. In particular, a boundary between an area where the output part is polarized and an area where it is not polarized (outer end side) exists at a portion, in which the secondary side electrodes  4 ,  4 A are provided. The boundary portion is structurally fragile, so that it is preferable that a slit  7  is provided at that portion, because loads are not applied to the portion.