JPH08195513A - Piezoelectric transformer - Google Patents

Abstract

PURPOSE: To lessen an input-side impedance and to prevent migration under high humidity by a method wherein internal electrode layers in a part of a rectangular board which face each other in the direction of thickness are made poles for ceramic polarization and poles for a transformer input, while internal electrodes in the other part which are provided on the lateral sides of this part and face each other are made a pole ceramic polarization and a pole for a transformer output. CONSTITUTION: In one section of a rectangular board 11 of a piezoelectric transformer 10, internal electrode layers 12a to 12c and 13a to 13c are arranged in the direction of thickness in a manner of projection and they face each other with ceramic interposed. The internal electrode layers 12a to 12c are used and one side of poles for ceramic polarization and poles for a transformer input, while the internal electrode layers 13a to 13c are used as the other side of the poles for ceramic polarization and the poles for the transformer input. In the other section of the rectangular board 11, the piezoelectric transformer 10 has a pair of lateral electrodes 18 and 19 provided on the opposite long sides of the rectangular board 11 and facing each other, as a pole for ceramic polarization and a pole for a transformer output.

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 more particularly to a rectangular plate made of piezoelectric ceramics, in which electrodes for polarization and input / output are formed on the inside and the surface of the rectangular plate. The present invention relates to a piezoelectric transformer that utilizes resonance in the vertical direction.

[0002]

2. Description of the Related Art A high voltage power supply device of about several watts at 1 kV is used, although a large current value is not required for lighting static electricity generators and backlights of liquid crystal displays. At present, electromagnetic transformers are used for boosting these high-voltage power supply devices, but due to demands such as reduction of generated electromagnetic noise, low power consumption, and small and low profile of equipment, practical use of piezoelectric transformers has been realized. Is being considered.

FIG. 4 is a schematic perspective view showing a conventional piezoelectric transformer. In the piezoelectric transformer 30 which is a kind of the piezoelectric vibrator shown in FIG. 4, the rectangular plate 31 made of piezoelectric ceramic has a rectangular plate 31 out of the front and back surfaces of the rectangular plate 31.
Surface electrodes 32 and 33 facing each other in the thickness direction of the rectangular plate 31 are formed in approximately half of the length direction of the rectangular plate 31. Further, side electrodes 34 and 35 facing each other in the width direction of the rectangular plate 31 are formed on the remaining half of the long side surface of the rectangular plate 31 in the length direction of the rectangular plate 31. The rectangular plate 31 has the surface electrodes 32 and 33 at the arrow C in the figure.
Is polarized in the thickness direction of the rectangular plate 31, and
The portion between the side surface electrodes 34 and 35 is polarized in the width direction of the rectangular plate 31 as shown by an arrow D in the figure.

FIGS. 5A, 5B, and 5C are explanatory views of the operation principle of the piezoelectric transformer 30 shown in FIG. 4, and FIG. 5A is a sectional view of the rectangular plate 31 in the longitudinal direction. , (B) are displacement distributions when the rectangular plate 31 is vibrating in the one-wavelength resonance mode of longitudinal vibration, and (c) shows a strain distribution at that time. For convenience of explanation, each electrode is not shown,
The cross section is not shaded. In FIG. 5B, the symbol E indicates a node of resonance vibration.

Referring to FIG. 4A together with FIG. 5A, the surface electrode 33 is used as a ground terminal, and the rectangular plate 31 is formed on the surface electrode 32.
When a voltage having a frequency equal to the resonance frequency of the one-wavelength resonance mode in the length direction is applied, the rectangular plate 31 vibrates as shown in FIGS. 5B and 5C. At this time, a voltage is generated between the side surface electrodes 34 and 35 by the piezoelectric effect. Here, the input voltage applied to the surface electrode 32 and the output voltage generated between the side surface electrodes 34 and 35 will be described. The facing distance between the surface electrode 32 and the surface electrode 33 is the distance between the side surface electrodes 34 and 35. Small enough compared to
Moreover, since the areas of the front surface electrodes 32 and 33 are sufficiently larger than the areas of the side surface electrodes 34 and 35, the electrostatic capacitance on the input side is sufficiently larger than the electrostatic 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 input electrode spacing and the output electrode spacing.

For the static electricity generating device and the liquid crystal backlight,
There is a demand for low power consumption and low voltage driving. One of the methods to meet this requirement is to reduce the impedance on the input side of the piezoelectric transformer in the high voltage power supply device. In order to reduce the impedance on the input side, it has been proposed to reduce the thickness of the piezoelectric ceramic rectangular plate and make the input side electrode a laminated structure. For example, in one of two sections in the length direction of the rectangular plate, a pair of surface electrode layers facing each other on the front and back surfaces of the rectangular plate as a ceramic polarization pole and a transformer input pole and the thickness direction of the rectangular plate. Has a pair of facing electrode layers (may be a plurality of pairs) facing each other in the thickness direction, and has a pair of surface electrode layers and a pair of facing electrode layers with one pole and the other pole, respectively. Each of the long side surfaces of the rectangular plate is connected by the first and second common wiring layers, and the first and second common connection layers are respectively connected to the nodes of the resonance vibration of the rectangular plate among the long side surfaces of the rectangular plate. There has been proposed a piezoelectric transformer having an input portion structure that is formed as described above and is used as an external electrode for wiring to the outside.

[0007]

Meanwhile, silver or a silver-palladium alloy is generally used as the electrode material of the piezoelectric transformer. However, silver or a silver-palladium alloy easily ionizes when moisture in the atmosphere adheres to the silver or silver-palladium alloy with a voltage applied, and causes a so-called migration phenomenon. That is, when a piezoelectric transformer using silver or a silver-palladium alloy as an electrode material for a pair of surface electrodes is used in a high humidity environment, the insulation resistance decreases, and in the worst case, a short circuit may occur, leading to destruction of the piezoelectric transformer. There is.

As a measure for preventing the migration phenomenon, platinum or gold which is hard to be ionized may be used without using silver as an electrode material. However, platinum or gold is expensive and a piezoelectric transformer can be manufactured industrially at low cost. Is not suitable for. Alternatively, a hermetic seal may be used to seal the entire piezoelectric transformer including the electrodes to prevent the electrodes from coming into contact with moisture in the atmosphere. However, it is still unsuitable for industrially inexpensively manufacturing piezoelectric transformers. is there.

An object of the present invention is to provide a piezoelectric transformer which has a small impedance on the input side and has a high reliability in which a migration phenomenon does not occur even when used in a high humidity environment, and is inexpensive. It is to be.

[0010]

According to the present invention, in a piezoelectric transformer utilizing a resonance mode in the lengthwise direction of a rectangular plate made of piezoelectric ceramic, the rectangular plate has one and the other in the lengthwise direction. In the one section of the rectangular plate, at least one pair of internal electrode layers facing each other in the thickness direction of the rectangular plate as a ceramic polarization pole and a transformer input pole is divided into two sections. The first and second external electrode layers which have the first and second external electrode layers and which are respectively connected to the one pole and the other pole of the pair of internal electrode layers are provided on both long side surfaces of the rectangular plate. In the other section of the rectangular plate, a pair of side surface electrode layers facing each other on each of the long side surfaces of the rectangular plate are provided on the node as a ceramic polarization pole and a transformer output pole. A piezoelectric transformer is obtained, characterized in that.

According to the present invention, the first and second parts are also provided.
The external electrode layer and the pair of side electrode layers are covered with a flexible resin material to obtain the piezoelectric transformer.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A piezoelectric transformer according to an embodiment of the present invention will be described below with reference to the drawings.

[Embodiment 1] FIG. 1 is a perspective view showing a piezoelectric transformer according to Embodiment 1 of the present invention. FIG. 2 is a vertical cross-sectional view of the piezoelectric transformer in FIG. 1 taken along the line AA ′. In FIGS. 1 and 2, a piezoelectric transformer 10 is a piezoelectric transformer that utilizes a resonance mode in the length direction of a rectangular plate 11 made of piezoelectric ceramics.

The rectangular plate 11 is divided into two parts in the length direction (left and right direction in the drawing). Piezoelectric transformer 10
In the section of the rectangular plate 11 on the left side in FIG. 1, the internal electrode layers 12a, 12b, and 12c and the internal electrode layer 1 are provided inside.
3a, 13b, and 13c. Internal electrode layers 12a, 12b, 12c, 13a, 13b, and 1
3 c are arranged in a projecting manner in the thickness direction of the rectangular plate 11 and face each other via ceramics. Further, the internal electrode layers 12a, 12b and 12c, the internal electrode layer 13a,
13b and 13c are connected by external electrode layers 16 and 17 on the long side surfaces of the rectangular plate 11, respectively. With such a structure, the internal electrode layers 12a, 12b and 12c serve as one of the ceramic polarization pole and the transformer input pole, and the internal electrode layers 13a, 13b and 13c serve as the ceramic polarization pole and the transformer input pole. Used as the other. That is, at least one pair of internal electrode layers may be provided in order to receive the ceramic polarization pole and the transformer input pole. Further, the external electrode layers 16 and 17 should be formed at a point where the amplitude when the rectangular plate 11 vibrates is zero, that is, on the node of resonance vibration. Regarding the support when the piezoelectric transformer 10 is arranged in an electric circuit or the like, since it is preferable to support at the node of resonance vibration, the external electrode layers 16 and 17 are used.

Further, the piezoelectric transformer 10 includes a rectangular plate 11
1 has a pair of side surface electrode layers 18 and 19 facing each other on both long side surfaces of the rectangular plate 11 as a ceramic polarization pole and a transformer output pole, respectively.

Next, a method of manufacturing the piezoelectric transformer 10 according to the first embodiment of the present invention will be described.

First, seven green sheets having a width of 10 mm, a length of 40 mm and a thickness of 230 μm and made of PZT type piezoelectric ceramics are prepared. A predetermined electrode pattern to be an internal electrode layer is printed on one surface of six of the seven green sheets with an electrode paste made of silver-palladium. These 6 print sheets are laminated, and further, one green sheet without an electrode pattern is laminated on this,
Crimp. After printing predetermined electrode patterns to be the external electrode layers 16 and 17 and the side surface electrode layers 18 and 19 on the long side surfaces of this laminated body, they are sintered in the atmosphere.

The piezoelectric transformer 10 manufactured as described above has a width of 10 mm, a length of 40 mm, and a thickness of 1 mm, and has a one-wavelength resonance mode. The node of resonance vibration is located 10 mm from the end face. The polarization of the piezoelectric ceramics of the rectangular plate 11 is as follows: temperature 150 ° C., electric field strength 1.2 kV /
mm.

The performance of the piezoelectric transformer 10 according to the first embodiment has a resonance frequency of 81.0 KHz and an irresistible resistance of 100 K.
When Ω, the output voltage was 500 V with respect to the input voltage 5 V, and the step-up ratio was 100.

[Embodiment 2] FIG. 3 is a longitudinal sectional view showing a piezoelectric transformer according to Embodiment 2 of the present invention. In FIG. 3, the same parts as those of the first embodiment or the same parts are designated by the same reference numerals as those in FIGS. 1 and 2. 3, in the piezoelectric transformer 10 ′, the rectangular plate 11 is divided into two in the lengthwise direction, like the piezoelectric transformer 10 according to the first embodiment, and in one division, the internal electrode layer 12 a, 1
2b, 12c and internal electrode layers 13a, 13b, and 13
c, and these internal electrode layers are connected by the external electrode layers 16 and 17 on the long side surface of the rectangular plate 11. Also,
Although not shown, the other section of the rectangular plate 11 has a pair of side surface electrode layers facing each other on both long side surfaces of the rectangular plate 11, as in the first embodiment.

Further, the piezoelectric transformer 10 according to the second embodiment.
In ′, the external electrode layers 16 and 17 and a pair of side electrode layers (not shown) are covered with a resin layer 21 made of a flexible elastic epoxy resin. In FIG. 3, the external electrode layer 1
Unlike Example 1, 6 and 17 do not reach the front and back surfaces of the rectangular plate 11. This is to prevent the resin layer 21 coated on the external electrode layers 16 and 17 from protruding from the outer shape of the piezoelectric transformer 10 ′ (in the thickness direction of the rectangular plate 11), but a slight protrusion may cause inconvenience. If not, the external electrode layers 16 and 17 may be formed so as to reach the front and back surfaces of the rectangular plate 11 as in the first embodiment.
In any case, the external electrode layers 16 and 17 may be formed on the nodes of the resonance vibration of the rectangular plate of the long side surfaces of the rectangular plate 11.

The piezoelectric transformer 10 'according to the second embodiment also has the same manufacturing process as the piezoelectric transformer 10 according to the first embodiment (the polarization of the piezoelectric ceramic is 150 ° C., the electric field strength is 1.2).
In addition to (implemented at kV / mm), a resin layer 21 is coated. The piezoelectric transformer 10 '(width 10 mm, length 40 mm, thickness 1 mm) has a resonance frequency of 8
When the input voltage is 5V, the output voltage is 485V, and the step-up ratio is 97 when the resistance is 0.5KHz and the resistance is 100KΩ.
Met.

Next, the piezoelectric transformers 10 and 10 'according to Examples 1 and 2 and the piezoelectric transformer 30 according to the conventional example shown in FIG. 4 as comparative examples (both using silver-palladium as an electrode material, Is 10 mm wide,
In order to evaluate the reliability in a high humidity environment of 40 mm in length and 1 mm in thickness), the failure rate when continuously driven in a high humidity environment (temperature 85 ° C., relative humidity 90%) was tested.
Table 1 shows the test results. Both the piezoelectric transformers 10 and 10 'according to Examples 1 and 2 were supported by their resonant vibration nodes.

[0024]

[Table 1]

Referring to Table 1, it can be seen that the piezoelectric transformer according to the present invention is more reliable in a high humidity environment than the conventional piezoelectric transformer using the same silver-palladium alloy as the electrode material.

[0026]

In the piezoelectric transformer according to the present invention, the rectangular plate is divided into one section and the other section in the longitudinal direction, and in one section of the rectangular plate, the rectangular plate is arranged inside the rectangular plate in the thickness direction of the rectangular plate. At least one pair of facing internal electrode layers is provided as a ceramic polarization pole and a transformer input pole, and is connected to one pole and the other pole of the pair of internal electrode layers on each of the long side surfaces of the rectangular plate. Having a first and a second external electrode layer on the node of the resonant vibration of the rectangular plate,
In the other section of the rectangular plate, since the pair of side surface electrode layers facing each other on both long side surfaces of the rectangular plate are provided as the ceramic polarization pole and the transformer output pole, the impedance on the input side is small. Of course, the migration phenomenon does not occur even if silver or a silver-palladium alloy is used as the electrode material in a high humidity environment. That is, of course, it has high reliability,
It is cheap.

[Brief description of drawings]

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

FIG. 2 is a vertical sectional view of the piezoelectric transformer shown in FIG.

FIG. 3 is a vertical sectional view showing a piezoelectric transformer according to a second embodiment of the present invention.

FIG. 4 is a perspective view showing a piezoelectric transformer according to a conventional example.

5A and 5B are views for explaining the operation of the piezoelectric transformer shown in FIG. 4, in which FIG. 5A is a cross-sectional view of a rectangular plate, and FIG. 5B is a rectangular plate vibrating in a longitudinal half-wavelength resonance mode. And (c) shows the strain distribution at that time.

[Explanation of symbols]

 10, 10 ', 30 Piezoelectric transformer 11, 31 Rectangular plate 12a, 12b, 12c Internal electrode layer 13a, 13b, 13c Internal electrode layer 16, 17 External electrode layer 18, 19, 34, 35 Side electrode layer 32, 33 Surface electrode layer

Claims (2)

[Claims] 1. A piezoelectric transformer utilizing a resonance mode in a longitudinal direction of a rectangular plate made of piezoelectric ceramics,
The rectangular plate is divided into one section and the other section in the length direction, and in the one section of the rectangular plate, a pair of internal electrodes facing each other in the thickness direction of the rectangular plate inside the rectangular plate. At least one pair of layers as ceramics polarization poles and transformer input poles, and first and second electrodes respectively connected to one pole and the other pole of the pair of internal electrode layers on each of both long side surfaces of the rectangular plate. A second external electrode layer is provided on a node of resonance vibration of the rectangular plate, and in the other section of the rectangular plate, a pair of side surface electrode layers facing each other on both of the long side surfaces of the rectangular plate. A piezoelectric transformer having a ceramic polarization pole and a transformer output pole. 2. The piezoelectric transformer according to claim 1, wherein the first and second external electrode layers and the pair of side electrode layers are covered with a flexible resin material.