JP3008255B2 - Piezoelectric transformer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer using piezoelectric ceramics. The present invention relates to a piezoelectric transformer using resonance.

[0002]

2. Description of the Related Art A high voltage power supply of about 1 kV to several watts is used for a static electricity generating device or for lighting a backlight of a liquid crystal display. At present, electromagnetic transformers are used as boosters for these power supplies, but due to demands such as reduction of generated electromagnetic noise, lower power consumption, and downsizing of equipment, the study of practical use of piezoelectric transformers has been considered. It has been done.

FIG. 3 is a schematic perspective view of the structure of a piezoelectric vibrator used in a conventional piezoelectric transformer. In FIG. 3, a piezoelectric ceramic rectangular plate 31 has electrodes 32 and 33 opposed to a half part in the length direction in the thickness direction.
Are formed. Also, the piezoelectric ceramic rectangular plate 31
Side electrodes 34 and 35 are formed on the long side surface of. In the piezoelectric ceramic rectangular plate 31, electrodes 32,
The portion 33 is polarized in the thickness direction, and the portion between the side electrodes 34 and 35 is polarized in the width direction of the piezoelectric ceramic rectangular plate 31.

FIG. 4 is an explanatory view of the operation principle of a piezoelectric transformer using the piezoelectric vibrator of FIG. 3, wherein FIG. 4 (a) is a sectional view of a piezoelectric ceramic rectangular plate, and FIG. 4 (b) is a piezoelectric ceramic rectangular plate. Fig. 4 (c) shows a displacement distribution when vibrating in the one-wavelength resonance mode of longitudinal vibration, and Fig. 4 (c) shows a strain distribution at that time. In FIG. 4A, when the electrode 33 is used as a ground terminal and a voltage having a frequency equal to the resonance frequency of the one-wavelength resonance mode in the longitudinal direction of the piezoelectric ceramic rectangular plate is applied to the electrode 32, the rectangular plate becomes And vibrate as shown in FIG. At this time, a voltage is generated between the side electrodes 34 and 35 by a piezoelectric effect. Here, the input voltage applied to the electrode 32 and the output voltage generated between the side electrodes 34 and 35 will be described. The facing distance between the electrode 32 and the electrode 33 is sufficiently smaller than the distance between the side electrodes 34 and 35. Since the area of 32, 33 is sufficiently larger than the area between the side electrodes 34 and 35, the capacitance on the input side is a value sufficiently larger than the capacitance on the output side. Therefore, when a vibrator is vibrated by applying a low voltage to the input side, a large voltage is generated on the output side in proportion to the ratio between the distance between the input side electrodes and the output side electrodes and the capacitance.

[0005]

However, the surface electrode has a problem in that the electric field is concentrated at the end of the surface electrode during the polarization of the ceramics, and the surface electrode is severely short-circuited, resulting in breakdown of the piezoelectric transformer. In addition, silver or silver-palladium alloy is easily ionized when moisture in the air adheres to the electrodes in a state where a voltage is applied, causing a so-called migration phenomenon. If used, insulation resistance will be reduced,
There is a problem that the piezoelectric transformer is broken. As a method for preventing migration, it is conceivable to use platinum or gold, which is difficult to ionize, as an electrode material. However, platinum and gold are expensive, and a piezoelectric transformer cannot be industrially produced at low cost.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the conventional structure by avoiding short-circuiting during polarization of ceramics and destruction of a piezoelectric transformer, low cost, and generation of migration even when used in a high humidity environment. SUMMARY OF THE INVENTION An object of the present invention is to provide a piezoelectric transformer having a structure capable of obtaining high reliability.

[0007]

According to the present invention, there is provided a piezoelectric transformer utilizing a longitudinal resonance mode of a rectangular plate made of piezoelectric ceramics, in which four corners are reduced.
Having a plurality of pairs of facing electrode layers facing in the thickness direction of the rectangular plate provided as a ceramic polarization electrode and a transformer input electrode, and the facing electrode layer faces a long side surface of the rectangular plate. And a first common wiring layer connected to the convex portion extending toward one long side and a convex portion extending toward the other long side. A piezoelectric transformer characterized by having a second common wiring layer to be connected is obtained.

Further, according to the present invention, there is provided a piezoelectric transformer wherein the plurality of pairs of facing electrode layers are provided inside the rectangular plate without being exposed to the surface thereof.

[0009]

The facing electrode, which is the electrode for ceramic polarization and the electrode for transformer input, has the corners of the four corners of the rectangle dropped, so that the electric field can be prevented from being concentrated at the four corners of the rectangle during the polarization of the ceramics. A piezoelectric transformer that does not short-circuit or break with an electrode layer provided on the long side surface of the section can be obtained. Also,
By having all of the facing electrode layers inside, a piezoelectric transformer that does not cause migration even when used in a high-humidity environment and has high reliability can be obtained at low cost.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the piezoelectric transformer according to the present invention will be described below in detail with reference to FIG.

With the center of the piezoelectric ceramic rectangular plate 11 in the longitudinal direction as a boundary, one of the left and right sections (the left section in the present embodiment) from the boundary (the left section in this embodiment) faces the piezoelectric ceramic rectangular plate 11 in the thickness direction. Two facing electrode layers 12
a, 12b, and 12c are provided as a ceramic polarization electrode and a transformer input electrode. Facing electrode layer 12
Each of a, 12b, and 12c is provided with a convex portion extending toward the long side surface of the piezoelectric ceramic rectangular plate 11 and extending in a direction different from each other. One of the protrusions extending toward the long side surface (the protrusions provided on the first, third, and fifth electrode layers from the top in the figure) is connected to the external electrode 14 as the first common wiring layer. are doing. The protruding portion extending toward the other long side surface (the protruding portion provided on the second, fourth, and sixth electrode layers from the top in the figure) is the external electrode 1 as a second common wiring layer.
5 is connected. In the other section (the right section in the present embodiment), the first and second surface electrode layers 15 and 20 are provided on both long side surfaces of the piezoelectric ceramic rectangular plate 11 as a ceramic polarization electrode and a transformer output electrode, respectively. 16.

Next, a specific method for manufacturing the piezoelectric transformer according to this embodiment will be described in detail. An internal electrode pattern is printed with a silver-palladium electrode paste on a 235-μm-thick green sheet of PZT-based piezoelectric ceramics, the printed sheet is laminated four layers, and a ceramic green sheet without an electrode pattern is laminated thereon, The laminate is thermocompressed and sintered in the atmosphere. Furthermore, the same electrode pattern as the electrode pattern previously formed inside by lamination is formed on the surface of the obtained sintered body using a silver paste. External electrodes 13 and 14 connected to the internal electrodes 12 are provided on the long side surfaces.
And the surface electrode 1 for polarization and output of the output part of the piezoelectric transformer
5, 16 are formed, length 40mm, width 10mm, thickness 1
1 mm resonance mode in the longitudinal direction. Since the nodes of the one-wavelength resonance mode are located at 10 mm from the end face of the piezoelectric ceramic rectangular plate in the longitudinal direction, the piezoelectric transformer supports the external electrodes and the surface electrode portions in the vicinity thereof, and leads the electrodes. It was a wire connection and take-out part. The polarization of piezoelectric ceramics is 150 °
The test was performed at an electric field strength of 1.2 kV / mm. The performance of this piezoelectric transformer has a resonance frequency of 81 kHz and a load resistance of 100 kΩ.
At this time, an input voltage of 5 V and an output voltage of 500 V resulted in a boost ratio of 100.

Table 1 shows the results of evaluating the yield of the piezoelectric transformer of Example 1 during polarization. For comparison, the piezoelectric transformer shown in FIG. 3 is also shown in Table 1 below.

[0014]

[Table 1] As apparent from Table 1, in the piezoelectric transformer having the structure of the present invention,
The yield during polarization is 100%, but in the comparative example, the yield is 20%.

Next, another embodiment of the piezoelectric transformer according to the present invention will be described with reference to FIG. The other embodiment shown in FIG. 2 and the above embodiment are the same except for the method of forming the internal electrodes. That is, the internal electrode 22 is different from the internal electrode 12 shown in FIG. 1 in that all the six layers of the electrodes are provided inside the piezoelectric ceramic rectangular plate 21. Therefore, there is no exposed portion of the electrode on the surface of the piezoelectric ceramic rectangular plate 21 as shown in FIG.

Next, a specific method for manufacturing a piezoelectric transformer according to another embodiment will be described in detail. An internal electrode pattern is printed with a silver-palladium electrode paste on a 210 μm and 60 μm thick green sheet of PZT-based piezoelectric ceramics, and a 60 μm printed sheet is laminated on top of 21 layers.
Five layers of 0 μm printed sheets are laminated, and one layer of 60 μm green sheets without an electrode pattern is laminated thereon, and the laminated body is thermocompression-bonded and sintered in air. Further, using silver paste, external electrodes 23 and 34 connected to the internal electrodes and surface electrodes 15 and 16 for polarization and output of the output portion of the piezoelectric transformer are formed on the long side surface of the obtained sintered body. , Length 40m
A piezoelectric transformer of one-wavelength resonance mode in the length direction with a width of 10 mm and a thickness of 1 mm is constructed. The performance of this piezoelectric transformer is as follows when the resonance frequency is 81.5 kHz and the load resistance is 100 kΩ.
A step-up ratio 102 of an output voltage of 510 V was obtained at an input voltage of 5 V.

In order to evaluate the reliability of the piezoelectric transformer of the second embodiment in a high humidity environment, a temperature of 85 ° C. and a relative humidity of 90%
A continuous drive test was performed under the following environment. For comparison, FIG.
Were also tested at the same time, and the results are shown in Table 2 below.

[0018]

[Table 2] It is clear from Table 2 that the piezoelectric transformer of the present invention has a continuous driving test 10
No failure occurred at 00 hours, but 100% failure in the comparative example.

[0019]

As described above in detail, according to the present invention, the piezoelectric transformer which does not short-circuit or break down when the ceramics are polarized, and which can be used at low cost even when used in a high humidity environment. It is possible to provide a piezoelectric transformer having a structure that does not generate and can obtain high reliability.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a structure of a piezoelectric transformer according to one embodiment of the present invention.

FIG. 2 is a perspective view showing a structure of a piezoelectric transformer according to another embodiment of the present invention.

FIG. 3 is a schematic perspective view showing the structure of a conventional piezoelectric transformer.

4A is a sectional view of a piezoelectric ceramic rectangular plate, and FIG. 4B is a displacement distribution diagram when the piezoelectric ceramic rectangular plate vibrates in a longitudinal one-wavelength resonance mode;
(C) is a diagram showing the strain distribution at that time.

[Explanation of symbols]

 11, 21 Piezoelectric ceramic rectangular plate 12, 22 Internal electrode layer 13, 14, 23, 24 External electrode 15, 16 Surface electrode

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 41/107

Claims (2)

(57) [Claims] 1. A piezoelectric transformer utilizing the resonance mode in the length direction of the rectangular plate made of a piezoelectric ceramic, the four
It has a shape with corners dropped, and has a plurality of pairs of facing electrode layers facing in the thickness direction of the rectangular plate provided as a ceramic polarization electrode and a transformer input electrode, and the facing electrode layer is Protrusions extending toward the long side of the rectangular plate and extending in different directions are provided, and further, the first common wiring layer connected to the protrusion extending toward one long side and the other long side. A piezoelectric transformer comprising a second common wiring layer connected to a protruding portion extending toward the piezoelectric transformer. 2. The piezoelectric transformer according to claim 1, wherein
A piezoelectric transformer, wherein the plurality of pairs of facing electrode layers are provided inside the rectangular plate without being exposed to the surface thereof.