JPH10112561A - Piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric transformer which can sharply reduce the deterioration of mechanical strength caused by the polarization of a piezoelectric plate, by lightening the concentration of the stress accompanying the polarization. SOLUTION: Roughly quadrangular input electrodes 2a and 2b are made in opposition at both main faces of the half on one side in longitudinal direction of a piezoelectric plate 1, and an output electrode 3 is made at the end face in longitudinal direction on the other side, and the sections where the input electrodes 2a and 2b to serve as an input part A are made are polarized in thickness direction as shown in an arrow P1, and the complementary half on the other side to serve as an output part B is polarized in longitudinal direction as shown in an arrow P2. For the input electrodes 2a and 2b, both corners on the side of boundary with the output part B are chamfered with straight lines.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piezoelectric transformer used for an inverter for a backlight of a liquid crystal display, an inverter for lighting a fluorescent tube, and the like.

[0002]

2. Description of the Related Art Conventionally, a piezoelectric transformer of this type is, for example, as shown in FIGS.
Square input electrodes 2 on both main surfaces in one half of the length direction
a and 2b are formed to face each other, and the output electrode 3 is formed on the other end surface in the longitudinal direction.
The portion where a and 2ba are formed is polarized in the thickness direction as indicated by arrow P1, and the other half of the output side B is polarized in the length direction as indicated by arrow P2.

This piezoelectric transformer uses a fundamental (primary) vibration mode in the longitudinal direction called a λ / 2 mode, and its vibration is generated in the vicinity of （(λ / 4) in the longitudinal direction. This is a so-called node point where the vibration displacement becomes zero. Input side wirings 4a and 4b are connected to positions corresponding to the node points of the input electrodes 2a and 2b, and an output side wiring 5 is connected to the output electrode 3. One input side wiring 4b is a common end (earth) for input and output. Then, the input electrodes 2a, 2b
An input voltage is applied through the input side wirings 4a and 4b between
By the action of the piezoelectric effect and the inverse piezoelectric effect, a boosted output voltage generated at the output electrode 3 is taken out through the output side wiring.

A piezoelectric transformer using a second-order or longer vibration mode uses a piezoelectric plate having a length that is an integral multiple of λ / 2, and has input electrodes formed on both main surfaces facing each other. And an output part polarized in the length direction and partially formed with an output electrode are arranged adjacent to each other in the length direction, and the center of each λ / 2 section in the length direction is arranged. A node point is generated in the vicinity, and the maximum displacement occurs near both ends and the position of each λ / 2 from the end. For example, in the case of the secondary vibration mode, in the piezoelectric transformer shown in FIGS. 5 and 6, the vicinity of the center in the length direction of the input electrodes 2a and 2b is a node point,
The input side wirings 4a and 4b are connected near the center of the input electrodes 2a and 2b in the longitudinal direction.

[0005]

However, in the conventional piezoelectric transformer, all four corners of the input electrodes 2a and 2b are formed at right angles, and the boundary between the input electrodes 2a and 2b and the output portion B (see FIG. 1). In FIG. 6, a portion C indicates a residual strain at the time of polarization in the thickness direction of the input portion A (elongation in the thickness direction).
Therefore, there is a problem that stress concentrates due to residual strain (elongation in the length direction) at the time of polarization in the length direction of the output portion B, and the mechanical strength of this portion is largely deteriorated.

Further, in the basic mode, stress concentrates on this portion during operation, so that the mechanical strength is likely to deteriorate in the operating state.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a piezoelectric transformer capable of relieving stress concentration caused by polarization and greatly reducing deterioration of mechanical strength due to polarization of a piezoelectric plate.

[0008]

According to a first aspect of the present invention, there is provided a rectangular piezoelectric plate having an input portion formed on both main surfaces and having an input portion polarized in a thickness direction. ,
An output part polarized in the length direction and an output part partially formed with an output electrode is a piezoelectric transformer arranged adjacent to the length direction, wherein the input electrode is at least a boundary corner of the output part. One is chamfered.

According to a second aspect of the present invention, in the piezoelectric transformer according to the first aspect, the chamfered input electrode comprises:
The area is at least 90% of the area before chamfering.

According to the above configuration, the corner on the boundary side of the output portion of the input electrode is chamfered, concentration of stress due to polarization at this portion is reduced, and deterioration of the mechanical strength of the piezoelectric plate is greatly reduced. Can be reduced.

Preferably, the area of the chamfered input electrode is set to 90% or more of the area before chamfering. That is, this chamfering reduces the area of the input electrode and lowers characteristics such as the step-up ratio.
The area of the input electrode and the coupling coefficient of the length vibration show a proportional relationship, and the area of the chamfered input electrode is 9 times the area before chamfering.
If it is 0% or more, the coupling coefficient of the length vibration can be made 90% or more, and the reduction of the step-up ratio can be reduced to about 1 which is practically allowable.
It can be suppressed to within dB.

Note that the area of the input electrode in the present invention is the total area of all the input electrodes.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the drawings showing embodiments thereof.

FIG. 1 shows the configuration of a piezoelectric transformer according to a first embodiment of the present invention. FIG. 1A shows a length vibration 1 of a single-plate structure.
Plane view of a secondary or secondary mode piezoelectric transformer, FIG.
(B) is a sectional view thereof.

As shown in FIG. 1, the piezoelectric transformer of this embodiment includes a piezoelectric plate 1 made of piezoelectric ceramics in the form of a rectangular flat plate. Rectangular input electrodes 2a and 2b are formed to face each other, and an output electrode 3 is formed on the other end surface in the longitudinal direction.
The portion where the input electrodes 2a and 2b serving as the input portion A are formed is polarized in the thickness direction by applying a DC voltage between the input electrodes 2a and 2b as shown by an arrow P1, and one side on the other side serving as the output portion B The half part is polarized in the length direction as shown by an arrow P2 by applying a DC voltage between the input electrodes 2a, 2b and the output electrode 3 with the input electrodes 2a, 2b short-circuited.

The input electrode 2a of the present embodiment is formed by straight chamfering both corners on the boundary side with the output portion B. Although not shown, the other input electrode 2b
Similarly to the input electrode 2a, both corners on the output section B side are chamfered and formed in the same shape as the input electrode 2a.

As described above, in the piezoelectric transformer of the present embodiment, both corners of the input electrodes 2a and 2b on the boundary side of the output portion B are chamfered, and stress concentration due to polarization in these portions is reduced. Therefore, the deterioration of the mechanical strength of the piezoelectric plate in this portion is greatly reduced. Therefore, a highly reliable piezoelectric transformer having high mechanical strength can be obtained.

Next, the effect of the chamfering of the input electrode on the characteristics will be described. FIG. 2 shows the area of the input electrode when the chamfer area of the input electrode is changed in the configuration of the present embodiment using a piezoelectric transformer of a vibration primary mode having a width of 8.5 mm and a length of 16.5 mm of the piezoelectric plate. FIG. 6 is a diagram showing the relationship between the coupling coefficient in the length direction. The electrode area and the coupling coefficient are standardized as 1 before chamfering (conventional configuration).

As shown in FIG. 2, the area of the input electrode and the coupling coefficient show a proportional relationship. As the chamfered area increases, the coupling coefficient of the longitudinal vibration decreases, and the characteristics such as the step-up ratio decrease slightly. I do. However, when the coupling coefficient of the length vibration is 90%, the reduction in the boost ratio is about 1 dB. When the area of the input electrode is 90% or more of the area before chamfering, the reduction in the boost ratio is practically acceptable. It can be suppressed within about 1 dB.

In the above-described embodiment, the chamfer is made by a straight line. However, the present invention is not limited to this, and the chamfer may be made by a curved line.

In the above-described embodiment, the input electrodes 2a and 2b on both main surfaces have the same shape and both corners on the output side of the input electrodes are chamfered in order to minimize the deterioration of mechanical strength. However, the present invention is not limited to this, and the chamfered shapes of the input electrode 2a and the input electrode 2b may be different, or only one of the corners may be chamfered. It only has to be chamfered.

That is, the shape, number, and the like of the chamfers can be appropriately set in relation to the mechanical strength and the electrical characteristics such as the step-up ratio.

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

The piezoelectric transformer of the present embodiment is a laminated primary or secondary vibration mode piezoelectric transformer. A rectangular flat piezoelectric plate 1 is formed by laminating a plurality of piezoelectric ceramic green sheets and integrally firing them. Is formed. Input electrode 2
a and 2b are formed alternately on the surface and inside of the piezoelectric plate 1, the input electrodes 2a of each layer are connected at one end face in the width direction, and the input electrodes 2b of each layer are connected at the other end face in the width direction. ing. The output electrode 3 is formed on the other end face in the length direction of the piezoelectric plate 1. The input electrode 2a of each layer and the input electrode 2b of each layer are separated by providing a gap 6 at one end face in the width direction.

The input electrodes 2a formed on the surface and the inner layers are formed in the same pattern as the input electrodes 2a formed on the surface, and both corners on the boundary side with the output portion B are rounded or curved. Beveled. Although not shown, the input electrode 2b of each layer is formed by chamfering both corners on the output portion B side similarly to the input electrode 2a.

In the piezoelectric transformer having such a laminated structure, similarly to the single-plate type piezoelectric transformer, the input electrodes 2a,
Stress is concentrated on the boundary between the output portion 2b and the output portion B (portion C shown in FIG. 3) due to the residual strain at the time of polarization in the thickness direction of the input portion A and the residual strain at the time of polarization in the length direction of the output portion B. Also,
Since the portion of the gap 6 peculiar to the laminated structure becomes a non-polarized region, stress is particularly concentrated on a boundary portion (portion D shown in FIG. 3) between the portion of the gap 6 and the polarized region, and the mechanical strength of this portion D Is particularly susceptible to deterioration.

For this reason, in the piezoelectric transformer having the laminated structure of the present embodiment, both corners of the input electrode of each layer on the output portion B side are chamfered, and the concentration of stress due to polarization in this portion is reduced. The deterioration of the mechanical strength of the piezoelectric plate at this portion is greatly reduced as compared with the case of the single-plate type piezoelectric transformer.

Also in this configuration, the electrode area and the coupling coefficient in the length direction have a substantially proportional relationship, and if the area of the input electrode is 90% or more of the area before chamfering, a reduction in the step-up ratio can be practically tolerated. It was confirmed that it could be suppressed within 1 dB.

FIG. 4 is a plan view of a piezoelectric transformer according to a third embodiment of the present invention.

The piezoelectric transformer of the present invention is a symmetric tertiary mode piezoelectric transformer, in which input electrodes 2... Are formed on both main surfaces at both ends in the length direction of the piezoelectric plate 1 and polarized in the thickness direction. Input parts A, A are arranged, and an output electrode 3 is formed between the input parts A, A, and an output part B polarized in the length direction is arranged.

Each input electrode 2 is chamfered at both corners on the boundary side with the output portion B by an R chamfer, that is, a curve.

As described above, the present invention can be applied to the case where the third or higher order vibration mode is used, and the same effects as those of the first and second embodiments can be obtained in the piezoelectric transformer of this embodiment. be able to.

[0033]

As described above, according to the piezoelectric transformer of the present invention, the corner of the input electrode on the boundary side with the output portion is chamfered, and the concentration of stress due to polarization at this portion is reduced. Therefore, deterioration of the mechanical strength of the piezoelectric plate in this portion can be significantly reduced. Therefore, according to the present invention, a highly reliable piezoelectric transformer having high mechanical strength can be obtained.

When the area of the chamfered input electrode is set to 90% or more of the area before chamfering, the reduction of the boosting ratio can be suppressed to about 1 dB which is practically allowable.

[Brief description of the drawings]

FIG. 1A is a plan view of a piezoelectric transformer according to a first embodiment of the present invention, and FIG. 1B is a cross-sectional view.

FIG. 2 is a diagram illustrating the relationship between the area of a chamfered input electrode and a coupling coefficient of longitudinal vibration.

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

FIG. 4 is a plan view of a piezoelectric transformer according to a third embodiment of the present invention.

FIG. 5 is a perspective view of a conventional piezoelectric transformer.

FIG. 6 is a plan view of a conventional piezoelectric transformer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric plate 2, 2a, 2b Input electrode 3 Output electrode A Input part B Output part

Claims (2)

[Claims] 1. A rectangular piezoelectric plate includes an input portion formed with input electrodes on both main surfaces and polarized in a thickness direction, and an output portion polarized in a length direction and partially formed with an output electrode. A piezoelectric transformer, which is disposed adjacently in a longitudinal direction, wherein the input electrode has at least one of corners on a boundary side of the output section chamfered. 2. The piezoelectric transformer according to claim 1, wherein an area of the chamfered input electrode is 90% or more of an area before the chamfering.