JPH08288566A - Piezoelectric transformer - Google Patents

Abstract

PURPOSE: To provide a piezoelectric transformer which has a low cost of the transformer generates no migration, even if the transformer is used under a high-temperature environment, a migration, and obtain a high reliability of the transformer. CONSTITUTION: Three pairs of facing electrode layers 12a, 12b and 12c, which face to the thickness direction of a rectangular piezoelectric ceramic plate 11, are provided as electrodes for ceramic polarization and electrodes for transformer input. The layers 12a, 12b and 12c are respectively provided with projected parts extended in the direction of their long side surfaces. The projected parts extended in the direction of the long side surfaces on one side of the long side surfaces of the layers are connected with an external electrode 14. The projected parts extended in the direction of the other long side surfaces of the layers are connected with an external electrode 15.

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, and in particular, electrodes for polarization and input / output are formed inside and on the surface of a rectangular plate of the piezoelectric ceramic, and the electrodes are arranged in the longitudinal direction of the rectangular plate. The present invention relates to a piezoelectric transformer that utilizes resonance.

[0002]

2. Description of the Related Art A high voltage power supply of about 1 kV-several watts is used for a static electricity generator or for lighting a backlight of a liquid crystal display without requiring a large current value. Currently, electromagnetic transformers are used for boosting these power supplies, but due to demands such as reduction of generated electromagnetic noise, low power consumption, and small and low profile of equipment, consideration of practical use of piezoelectric transformers is under consideration. 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, the piezoelectric ceramic rectangular plate 31 has electrodes 32 and 33 that are opposed to each other in the thickness direction in approximately half of the length direction.
Are formed. In addition, the piezoelectric ceramic rectangular plate 31
Side electrodes 34 and 35 are formed on the long side surface of the. In the piezoelectric ceramic rectangular plate 31, electrodes 32,
The portion 33 is polarized in the thickness direction, and the portion between the side surface electrode 34 and the side surface electrode 35 is polarized in the width direction of the piezoelectric ceramic rectangular plate 31.

4A and 4B are explanatory views of the operation principle of the piezoelectric transformer using the piezoelectric vibrator of FIG. 3, FIG. 4A is a sectional view of the piezoelectric ceramic rectangular plate, and FIG. 4B is a piezoelectric ceramic rectangular plate. Is the displacement distribution in the case of vibrating in the one-wavelength resonance mode of the longitudinal vibration, and FIG. 4C shows the 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 length direction of the piezoelectric ceramic rectangular plate is applied to the electrode 32, the rectangular plate is changed to the one shown in FIG. And vibrate as shown in (c). At this time, a voltage is generated between the side surface electrodes 34 and 35 due to the piezoelectric effect. Here, the input voltage applied to the electrode 32 and the output voltage generated between the side surface 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 surface electrodes 34 and 35. Since the areas of 32 and 33 are sufficiently larger than the area between the side surface electrodes 34 and 35, the capacitance on the input side becomes a value sufficiently larger than the capacitance on the output side. Therefore, when a low voltage is applied to the input side to vibrate the vibrator, a large voltage is generated on the output side in proportion to the ratio of the capacitance between the input side electrodes and the output side electrodes and the capacitance.

[0005]

However, in the surface electrode, there is a problem that the electric field is concentrated at the end portion of the surface electrode during the polarization of the ceramics, resulting in a serious short circuit, and the piezoelectric transformer is destroyed. Further, silver or a silver-palladium alloy is easily ionized when moisture in the atmosphere adheres to the electrode in a state where a voltage is applied and causes a so-called migration phenomenon. If used, insulation resistance will drop, and it will cause a serious short circuit,
There is a problem that the piezoelectric transformer is destroyed. As a method of preventing migration, it is conceivable to use platinum or gold, which is difficult to ionize, as an electrode material, but platinum or gold is expensive and a piezoelectric transformer cannot be industrially produced at low cost.

In order to solve the problems of the conventional structure, the object of the present invention is to prevent short-circuiting at the time of polarization of ceramics, to prevent the piezoelectric transformer from being broken, and at low cost, to cause migration even when used in a high humidity environment. Another object is to provide a piezoelectric transformer having a structure capable of obtaining high reliability.

[0007]

According to the present invention, in a piezoelectric transformer that utilizes a longitudinal resonance mode of a rectangular plate made of piezoelectric ceramics, the rectangular plate has a central portion in the longitudinal direction as a boundary, and left and right sides of the boundary. A plurality of pairs of facing electrode layers provided in one of the sections as ceramic polarization electrodes and transformer input electrodes and facing in the thickness direction of the rectangular plate, and in the other section, both sides of the rectangular plate. On the long side surface, there are provided a ceramic polarization electrode and a first and a second surface electrode layer provided as a transformer output electrode, respectively, and the facing electrode layer is directed toward the long side surface of the rectangular plate and to each other. The convex portions extending in different directions are provided, and the first common wiring layer connected to the convex portion extending toward one long side surface and the convex portion extending toward the other long side surface are connected. A piezoelectric transformer is obtained which is characterized in that it is configured by including a second common wiring layer.

Further, according to the present invention, there can be obtained a piezoelectric transformer characterized in that the plurality of pairs of facing electrode layers are provided inside the rectangular plate in a state of not being exposed at the surface of the rectangular plate.

[0009]

The ceramic polarization electrode and the facing electrode, which is the transformer input electrode, have the four corners of the rectangle dropped, so that the electric field can be prevented from concentrating at the four corners of the rectangle during ceramic polarization, and the other side of the rectangular plate can be prevented. It is possible to obtain a piezoelectric transformer that is neither short-circuited nor broken with the electrode layer provided on the long side surface of the section. Also,
By including all 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 in detail below with reference to FIG.

With the central portion of the piezoelectric ceramic rectangular plate 11 in the longitudinal direction as a boundary, one of the sections on the left and right of the boundary (the section on the left side in this embodiment) faces the piezoelectric ceramic rectangular plate 11 in the thickness direction. Pair of facing electrode layers 12
a, 12b and 12c are provided as ceramic polarization electrodes and transformer input electrodes. Facing electrode layer 12
Each of a, 12b and 12c is provided with a convex portion extending in a different direction toward the long side surface of the piezoelectric ceramic rectangular plate 11. The convex portion extending toward one of the long side surfaces (the convex portion provided on the first, third, and fifth electrode layers from the top of the figure) is connected to the external electrode 14 as the first common wiring layer. are doing. The convex portion extending toward the other long side surface (the convex portion provided on the second, fourth, and sixth electrode layers from the top of the drawing) is the external electrode 1 as the second common wiring layer.
It is connected to 5. In the other section (the right section in this embodiment), the first and second surface electrode layers 15 serving as ceramic polarization electrodes and transformer output electrodes are provided on both long side surfaces of the piezoelectric ceramic rectangular plate 11, respectively. It has 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, four layers of the printed sheet are laminated, and one layer of a ceramic green sheet having no electrode pattern is laminated thereon. The laminate is thermocompression bonded and sintered in the atmosphere. Further, using the silver paste, the same electrode pattern as the electrode pattern internally formed in advance by lamination is formed on the surface portion of the obtained sintered body. External electrodes 13 and 14 connected to the internal electrode 12 are provided on the long side surfaces.
And surface electrode 1 for polarization and output of piezoelectric transformer output
5 and 16 are formed, length 40mm, width 10mm, thickness 1
A piezoelectric transformer having a 1-wavelength resonance mode in the longitudinal direction of mm is constructed. In the piezoelectric transformer, since the nodes of the one-wavelength resonance mode are located 10 mm from the end faces in the length direction of the piezoelectric ceramic rectangular plate, they support the external electrodes and surface electrode parts in the vicinity thereof and lead the electrodes. It was used as a connection / extraction portion for the wire. The polarization of piezoelectric ceramics is 150 ° C,
The electric field strength was 1.2 kV / mm. This piezoelectric transformer has a resonance frequency of 81 kHz and a load resistance of 100 kΩ.
At this time, a boost ratio 100 with an input voltage of 5 V and an output voltage of 500 V was obtained.

Table 1 shows the results of evaluation of 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 is clear 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-described 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 electrode layers 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 green sheet of PZT-based piezoelectric ceramics having a thickness of 210 μm and 60 μm, and a 60 μm printed sheet is laminated on one layer 21
Five layers of 0 μm printed sheets are laminated, one layer of 60 μm green sheet without an electrode pattern is laminated thereon, and the laminate is thermocompression bonded and sintered in the atmosphere. Further, the silver paste is used to form the external electrodes 23 and 34 connected to the internal electrodes and the surface electrodes 15 and 16 for polarization and output of the output portion of the piezoelectric transformer on the long side surfaces of the obtained sintered body. , Length 40m
A piezoelectric transformer of m, width of 10 mm, and thickness of 1 mm in the longitudinal direction single wavelength resonance mode is constructed. The performance of this piezoelectric transformer is 81.5 kHz at resonance frequency and 100 kΩ load resistance,
A step-up ratio 102 with an input voltage of 5V and an output voltage of 510V was obtained.

In order to evaluate the reliability of the piezoelectric transformer of Example 2 in a high humidity environment, a temperature of 85 ° C.-90% relative humidity was used.
The continuous drive test was carried out under the environment. Figure 3 for comparison
The piezoelectric transformer shown in Table 1 was tested at the same time, and the results are shown in Table 2 below.

[0018]

[Table 2] As apparent from Table 2, in the piezoelectric transformer having the structure of the present invention, the continuous drive test was performed under the environment of temperature 85 ° C.-90% relative humidity.
Although no defect occurred at 00 hours, it is 100% defective in the comparative example.

[0019]

As described above in detail, according to the present invention, a piezoelectric transformer that is not short-circuited or destroyed during polarization of ceramics, and further, migration is possible 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 occur and has high reliability.

[Brief description of drawings]

FIG. 1 is a perspective view showing a structure of a piezoelectric transformer according to an 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 cross-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 single wavelength resonance mode,
(C) is a diagram showing a 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

Claims (2)

[Claims] 1. A piezoelectric transformer using a resonance mode in the lengthwise direction of a rectangular plate made of piezoelectric ceramics, wherein ceramics polarization is applied to one of the left and right sections of the rectangular plate as a boundary. Electrodes and transformer input electrodes, a plurality of pairs of facing electrode layers facing each other in the thickness direction of the rectangular plate, and the other section, on both long side surfaces of the rectangular plate, ceramic polarization electrodes and A first and a second surface electrode layer provided as a transformer output electrode, wherein the facing electrode layer is
The rectangular plate is provided with convex portions extending in different directions toward the long side surface, and further, the first common wiring layer connected to the convex portion extending toward one long side surface and the other long side. A piezoelectric transformer comprising a second common wiring layer connected to a convex portion extending toward a side surface. 2. The piezoelectric transformer according to claim 1, wherein
A piezoelectric transformer, wherein a plurality of pairs of facing electrode layers are provided inside the rectangular plate in a state of not being exposed at the surface of the rectangular plate.