JPH11163431A - Multilayer piezoelectric transformer - Google Patents

Abstract

(57) [Summary] [Object] To provide a multilayer piezoelectric transformer which has high reliability, in which delamination hardly occurs, and which has an inductive reactance for reducing an inrush current. The laminated piezoelectric transformer includes an interlayer drive electrode 17 inserted between layers of the thin plate-shaped piezoelectric bodies 1a... Inside the laminate.
Is not a flat plate, but has a spiral notch K of not less than 3/4 circumference, and sandwiches the interlayer drive electrodes 17 having the spiral notch K from both sides in a sandwich shape. Adjacent ones of the thin plate-like piezoelectric bodies 1a are joined to each other at the cuts K (which are gaps between the electrodes) to strengthen the bonding of the laminated body, prevent delamination, and remove the notches K. The ceramic material to be buried and joined serves as a wall for preventing the penetration of moisture into the center of the driving portion of the laminated body, preventing migration, and further reducing the inrush current due to the inductive reactance of the spiral driving pattern of the interlayer driving electrode 17. It is a structure to make it.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer used for a discharge lamp lighting device for backlighting a liquid crystal panel, a high voltage power supply such as a copying machine and an ozone generator and a power supply device such as a DC-DC converter. More specifically, the present invention relates to an improvement in an interlayer drive electrode of a multilayer piezoelectric transformer.

[0002]

2. Description of the Related Art The basic structure of a piezoelectric transformer is such that a rectangular plate-like piezoelectric material (for example, a barium titanate or lead zirconate titanate (PZT) -based piezoelectric ceramic material) in a longitudinal direction in a perspective view of FIG. On the other hand, a pair of input terminal electrodes 2a and 2b facing each other in the thickness direction is formed, and an output terminal electrode 3 is formed on the other end face in the longitudinal direction. It is configured to be polarized in the thickness direction (down arrow) and to polarize the output-side piezoelectric body, which is the power generation unit, in the longitudinal direction (right arrow) (referred to as a Rosen-type piezoelectric transformer).

When an input voltage having a natural resonance frequency determined by the longitudinal shape of the piezoelectric body 1 is applied between the input terminal electrodes 2a and 2b, the piezoelectric body 1 causes mechanical vibration in the longitudinal direction due to an electrostrictive effect. The AC high voltage generated by the piezoelectric effect is extracted from the output terminal electrode 3 on the other side.

The step-up ratio of the piezoelectric transformer is determined by the longitudinal dimension and the thickness of the piezoelectric body 1. The step-up ratio increases as the longitudinal dimension increases and as the thickness decreases. However, it has been difficult to realize a piezoelectric transformer having a practically sufficient step-up ratio due to a problem in manufacturing and a problem in mechanical strength.

In order to solve the above problem and obtain a sufficient boosting ratio, in FIG. 4, the piezoelectric body 1 has a laminated structure in which a plurality of thin plate-like piezoelectric bodies 1a, 1b, 1c,. A multilayer piezoelectric transformer has been devised. In this laminated piezoelectric transformer, in addition to the input terminal electrodes 2a, 2b, the laminated piezoelectric members 1a, 1b, 1c,... And the interlayer drive electrodes 7, 5, 8, 6 inserted between the layers of each piezoelectric member. Are alternately laminated, and the electrodes of each layer are alternately provided with a pair of input terminal electrodes 2a and 2a.
b. That is, in FIG. 4, the interlayer drive electrodes 7 and 8 are connected to the input terminal electrode 2b, and the interlayer drive electrodes 5 and 6 are connected to the input terminal electrode 2a.

[0006] By forming the piezoelectric transformer in a laminated structure, the substantial thickness between the input terminal electrodes can be reduced, so that a small-sized piezoelectric transformer having a sufficiently high step-up ratio for practical use can be obtained. It became.

However, in the above-mentioned laminated piezoelectric transformer, the bonding between the electrode material and the piezoelectric ceramic material in the laminated structure is weakened due to mechanical vibration or shock due to long-term use, and delamination occurs, causing the piezoelectric transformer to be deflected. There is a problem that characteristics are deteriorated.

In this regard, Japanese Patent Application Laid-Open No. 9-69657 discloses that in order to solve the problem of delamination, as shown in FIG. As the drive electrode 9 or the interlayer drive electrode 10 in the form of a stripe as shown in FIG. 3B, the area (gap) where the piezoelectric bodies on both sides of the interlayer drive electrode 9 or 10 are joined to each other is increased so that they are difficult to peel off. The disclosed stacked piezoelectric transformer is disclosed.

As a second problem of the multilayer piezoelectric transformer, when it is used for a long time in a high-temperature and high-humidity state, moisture penetrates from the delaminated part of the outer peripheral portion of the piezoelectric body and reaches the inside to cause migration. There was a problem.

On the other hand, a piezoelectric transformer generally has the highest conversion efficiency when driven by a non-steep rounded voltage waveform (for example, a sine wave input voltage) having a single frequency component corresponding to its resonance frequency. It is desirable that the inrush current flowing into the input capacitance of the section be as small as possible. In this regard, conventionally, as a measure for reducing the rush current to the input electrode side, a measure such as inserting a capacitor or an inductor element between the drive circuit of the piezoelectric transformer and the input electrode has been adopted.

It should be noted that recently, as shown in the perspective view of FIG.
Japanese Patent Laid-Open No. Hei 9-162 discloses a piezoelectric transformer having a meandering pattern D in which an electrode b and an interlayer drive electrode (not shown) form an inductor.
No. 456.

[0012]

However, with respect to the problem of delamination, the means using the mesh-like or stripe-like interlayer drive electrodes 9 and 10 requires a portion where the ceramic material as the piezoelectric material is bonded (that is, the portion where the ceramic material is bonded). , The notch portion of the electrode) is composed of a plurality of small joined portions, so that the structure is weak against the invasion of moisture into the center of the piezoelectric body driving portion (after all, the moisture is formed by the piezoelectric body). The center portion of the driving portion is reached immediately from the slight delamination portion on the outer periphery through the thin mesh-like or comb-like interlayer driving electrodes 9 and 10).

In order to reduce the number of components and the mounting area of the power supply device, it is desirable that the piezoelectric transformer itself be provided with a measure against the rush current. In the above-described means in which the interlayer drive electrode itself forms a meandering pattern forming an inductor, inductive reactance is not so large, and cannot be said to be an effective means. An inductor of about several turns is not sufficient for the entire piezoelectric body in which the patterns of the interlayer drive electrodes are stacked.

The present invention has been made in view of the above problems, and in the multilayer piezoelectric transformer, while devising a pattern of an interlayer drive electrode in which delamination hardly occurs,
At the same time, it is an object of the present invention to realize a laminated piezoelectric transformer in which the input electrode pattern itself has a sufficient inductive reactance.

[0015]

In order to solve the above-mentioned problems, the present invention provides: (1) a laminated body in which a plurality of thin plate-shaped piezoelectric bodies are superimposed, and a different laminated body on an outer surface corresponding to a driving portion of the laminated body. A pair of input terminal electrodes formed facing the position, an output terminal electrode formed in a power generation unit of the laminate, and an inside of the laminate that is conductively connected to one of the pair of input terminal electrodes. And at least one of the interlayer drive electrodes conductively connected to one of the input terminal electrodes has a length of at least 3/4 turn. A laminated piezoelectric transformer having a spiral cutout, wherein the thin plate-shaped piezoelectric bodies sandwiching the interlayer drive electrode from both sides are joined by cutting the interlayer drive electrode. .

(2) The spiral cutout is
The multilayer piezoelectric transformer according to the above (1), which is formed by being divided into one or more blocks, is provided.

(3) The gap of the spiral pattern of the cutout of the interlayer drive electrode having the spiral cutout is thicker in a region near the outer periphery of the piezoelectric body, and the gap is narrower in a region closer to the center region. To provide a multilayer piezoelectric transformer according to the above (1) or (2).

(4) The above (1), (2) or (3), wherein the shape of the input terminal electrode is the same as that of the interlayer drive electrode having a spiral cutout.
The present invention provides a multilayer piezoelectric transformer described in (1).

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the following drawings.

FIG. 1 is a plan view for explaining an embodiment of an interlayer drive electrode in a multilayer piezoelectric transformer according to the present invention.

FIG. 2 is a view for explaining the cross-sectional structure of the drive section of the multilayer piezoelectric transformer according to the present invention.

FIG. 3 is a plan view for explaining another embodiment of the interlayer drive electrode in the multilayer piezoelectric transformer according to the present invention.

First, the appearance of the multilayer piezoelectric transformer of the present invention is the same as that of the multilayer piezoelectric transformer shown in FIG. That is, the plurality of thin plate-shaped piezoelectric bodies 1a, 1b,
1c, 1d, and 1e, and a pair of input terminal electrodes 2a and 2b formed at opposite positions on an outer surface corresponding to a driving unit A of the laminate to face each other; An output terminal electrode 3 formed in the portion B and an interlayer drive electrode which is conductively connected to one of the pair of input terminal electrodes 2a and 2b and is inserted between layers inside the laminate so as to be alternately opposed to each other. Is the same as the conventional one.

However, at least one (preferably all) of the interlayer driving electrodes inserted between the thin plate-like piezoelectric bodies 1a, 1b, 1c,... It is not a flat plate, for example, as shown in the plan view of FIG.
Has a spiral notch K of 、 ３ or more (three in the figure), and as shown in the sectional view of FIG.
Interlayer drive electrode 1 having spiral cutout K
Adjacent ones of the thin plate-like piezoelectric members 1a, 1b, 1c, 1d, and 1e sandwiching 5, 16, 17, 18 in a sandwich shape from both sides are sandwiched between the interlayer drive electrodes 15, 16, 1
It is characterized in that it is joined to each other at cuts 7 and 18 (which are gaps between electrodes).

That is, when forming the laminated body by thermocompression bonding, the ceramic materials of the thin plate-like piezoelectric bodies 1a, 1b, 1c, 1d and 1e sandwiching the interlayer drive electrode from both sides are formed in a spiral shape. Are joined together so as to fill the notch K. Of course, in this case, the area of the notch K filled with the piezoelectric material is connected without interruption.

According to the structure of the laminated piezoelectric transformer,
The interlayer drive electrodes 15, 16, 17, 18 are the input terminal electrodes 2
It will be apparent that delamination is less likely to occur than in the case of a flat plate similar to a and 2b (the joint between the thin plate-like piezoelectric members on both sides is only the outer peripheral portion of the drive unit).

Further, compared to the mesh-like or stripe-like interlayer drive electrodes 9 and 10 shown in FIG. 5, the spiral-like interlayer drive electrodes are connected to one and have a longer distance from the outer periphery toward the center. Because of the spiral structure that turns around, there is very little risk that moisture will penetrate through the electrode and enter the center. At the end, the cutout portions K filled with the piezoelectric ceramic material are continuously connected to one another, and the ceramic material filling the cutout K serves as a water wall toward the center. As a result, the structure is strong against the progress of the migration.

Further, according to the present invention, as shown in FIG. 1, at the portion near the outer periphery of the piezoelectric body where delamination is likely to occur,
The width d1 (gap between the electrodes) of the cutout K of the interlayer drive electrode pattern is increased to increase the area of the joining portion of the piezoelectric ceramic material, and the width d3 of the cutout K of the interlayer drive electrode pattern becomes closer to the center of the drive unit. (D1>d2> d3 in FIG. 1), and the interlayer at the outer peripheral portion of the driving portion of the piezoelectric transformer in which delamination is likely to occur. In addition to increasing the strength against peeling, the conductor resistance of the electrode at the center of the drive unit is kept low to prevent a decrease in conversion efficiency.

The interlayer drive electrodes 15, 16, 1
The spiral cutouts K (in other words, the spiral cutouts, which can be circular or rectangular in circumference) formed in the layers 7 and 18 can be seen from the contrary, the interlayer drive electrode is This is synonymous with the fact that one connected conductor forms a spiral coil pattern. Therefore, the interlayer drive electrode itself has inductive reactance, and the interlayer drive electrode has an action of reducing an inrush current flowing into the input capacitance of the drive unit of the multilayer piezoelectric transformer. As a result, the conversion efficiency does not decrease even when driven by a waveform having a sharp rise such as a rectangular wave.

Next, as shown in FIG. 3, the spiral pattern of the interlayer drive electrode is formed by dividing a spiral cut into two or more blocks K1 and K2. Conversely, this configuration is a spiral block 27a, 2
7b (but connected to one). It goes without saying that the same effect as described above can be obtained with the above configuration. In particular, in the case of an elongated laminate, it is effective to divide the spiral pattern into two or more blocks.

Further, it is understood that the spiral cutouts K may be formed on the interlayer drive electrodes so that the input terminal electrodes 2a and 2b may have spiral cutouts if they are extended. . That is, the input terminal electrodes 2a, 2
It has the same shape as the b-layer drive electrode. This structure can be said to be a structure capable of obtaining an even larger inductive reactance.

The laminated piezoelectric members 1a, 1a
The number of layers b,... is not limited and should be appropriately designed in order to obtain a desired step-up ratio with a predetermined external dimension.

[0033]

The multilayer piezoelectric transformer of the present invention is configured as described above. (1) Since the interlayer drive electrode has a spiral cutout, a thin plate-like piezoelectric body sandwiching both sides is joined. Has an effect that the delamination hardly occurs.

(2) In addition, the ceramic material joined by filling the spiral cut-out portion serves as a wall to prevent moisture from entering, and as a result, there is an effect that migration hardly occurs.

(3) Further, since the spiral pattern of the interlayer drive electrode and the input terminal electrode has inductive reactance itself, the rush current of the rectangular wave input is reduced, and the conversion efficiency is improved.

(4) Further, the width of the spiral notch is increased at a portion near the outer periphery of the piezoelectric body where delamination is likely to occur, so that the area of the joining portion of the piezoelectric ceramic material is increased, and the width of the spiral notch is increased at the center of the driving portion. Since the structure is reduced in width as approaching, it has the effect of increasing the strength against delamination and at the same time preventing the conversion efficiency from decreasing.

[Brief description of the drawings]

FIG. 1 is a plan view illustrating an embodiment of an interlayer drive electrode in a multilayer piezoelectric transformer according to the present invention.

FIG. 2 is a view for explaining a cross-sectional structure of a driving unit of the multilayer piezoelectric transformer according to the present invention.

FIG. 3 is a plan view for explaining another embodiment of the interlayer drive electrode in the multilayer piezoelectric transformer according to the present invention.

FIG. 4 is a perspective view showing the structure of a conventional piezoelectric transformer.

5A and 5B are perspective views showing interlayer drive electrodes in a conventional multilayer piezoelectric transformer, wherein FIG. 5A is a mesh type and FIG. 5B is a stripe type.

FIG. 6 is a perspective view of a conventional piezoelectric transformer having an input terminal electrode having a meandering pattern forming an inductor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Piezoelectric body 1a, 1b, 1c, 1d, 1e Thin plate-shaped piezoelectric body 2a, 2b, 12a, 12b Input terminal electrode 3 Output terminal electrode 5, 6, 7, 8, 9, 10, 15, 16, 17, 18
Interlayer drive electrode 27a, 27b Block of spiral pattern of interlayer drive electrode A Drive section B Power generation section D Meandering pattern d1, d2, d3 Notch width K, K1, K2 Spiral notch

Claims (4)

[Claims] 1. A laminated body in which a plurality of thin plate-shaped piezoelectric bodies are superimposed, a pair of input terminal electrodes formed opposite to each other on an outer surface corresponding to a driving unit of the laminated body, and the laminated body. An output terminal electrode formed in the power generation unit of the above, and an interlayer drive electrode which is conductively connected to each one of the pair of input terminal electrodes and is inserted between the inner layers of the stacked body so as to alternately face each other. In the laminated piezoelectric transformer provided, at least one of the interlayer drive electrodes conductively connected to one of the input terminal electrodes has a spiral cutout of 3/4 or more, and the thin plate sandwiching the interlayer drive electrode from both sides Wherein the plurality of piezoelectric members are joined to each other by cutting the interlayer drive electrode. 2. The multilayer piezoelectric transformer according to claim 1, wherein the spiral cutout is formed by dividing it into two or more blocks. 3. The gap of the spiral pattern of the cutout of the interlayer drive electrode having a spiral cutout is thicker in a region near the outer periphery of the piezoelectric body and narrower in a region closer to the center region. The multilayer piezoelectric transformer according to claim 1 or 2. 4. The multilayer piezoelectric transformer according to claim 1, wherein the shape of the input terminal electrode is the same as that of the interlayer drive electrode having a spiral cutout.