JPH09129941A - Piezoelectric transformer - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide a piezoelectric transformer that has good characteristics and is inexpensive because it is easy to handle by separating the piezoelectric plate from the outside by coating it with an exterior resin. SOLUTION: A piezoelectric plate 1 is supported and fixed to a substrate 10 by a flexible supporting member 21, and input electrodes 2a, 2 of the piezoelectric plate 1 are provided.
b, the output electrode 3 is a terminal electrode 12 formed on the substrate 10.
a, 12b, 13 are respectively connected by lead wires 6, and lead terminals 15 are connected to the respective terminal electrodes 12a, 12b, 13 respectively. Then, the piezoelectric plate 1 is the support member 2
1, the substrate 10 and the cavity 24 are separated from each other and covered with the exterior resin 23, and the lead terminals 15 are drawn out from the exterior resin 23.

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 an inverter for a backlight of a liquid crystal display, and more particularly to a structure covered with an exterior resin.

[0002]

2. Description of the Related Art As shown in FIG. 6, for example, a piezoelectric transformer of this type has an input electrode 2 on both main surfaces of one side half portion of a piezoelectric plate 1 made of piezoelectric ceramics on a rectangular flat plate.
a and 2b are formed, the output electrode 3 is formed on the end face in the lengthwise direction on the other side, and as shown by the arrow, the part where the input electrodes 2a and 2b on the input side are formed is polarized in the thickness direction, The other side, which is the output side, is polarized in the length direction.

Input side wirings 4a and 4b are connected to positions corresponding to the node points of the input electrodes 2a and 2b, and the output electrode 3
Is connected to the output side wiring 5. One input side wiring 4b serves as a common end (ground) for input and output.

Then, an input voltage is applied between the input electrodes 2a and 2b through the input side wiring, and the boosted output voltage generated at the output electrode 3 is taken out through the output side wiring 5 by the action of the piezoelectric effect and the inverse piezoelectric effect. Be done.

The piezoelectric transformer shown in FIG. 6 uses a basic (first-order) vibration mode called a λ / 2 mode, and its vibration is a vibration displacement at 1/2 (λ / 4) in the length direction. Is a so-called nodal point where it becomes zero, and the maximum displacement occurs at both ends.

Usually, this type of piezoelectric transformer is constructed by using a longitudinal vibration mode of an integral multiple of λ / 2. When a longitudinal vibration mode of a second order or higher is used, each λ / 2 section in the longitudinal direction. A node point is generated in the center of, and both λ /
The maximum displacement occurs at position 2, and the input electrode is formed in a section of λ / 2 from one end in the length direction.

In such a piezoelectric transformer, it is desirable to support the piezoelectric transformer at a position corresponding to the node point where the displacement is minimized so as not to hinder vibration as much as possible, and the electrical connection for input / output is also connected at the node point. Is desirable.

[0008]

As described above, the piezoelectric transformer utilizes the vibration of the entire piezoelectric plate, and the vibration displacement is large. Conventionally, as a packaging method for the piezoelectric transformer, the node is arranged so as to suppress the vibration as much as possible. Although methods such as devising support at points and storing in a case are being considered, the support structure becomes complicated, and when storing in a case, the sealing structure of the external terminal lead-out part becomes complicated, and There was a problem in practical use, such as an increase in the number of parts.

Therefore, an object of the present invention is to provide a piezoelectric transformer that is supported without suppressing vibrations and that can easily separate the piezoelectric plate from the outside, and that has good characteristics and is easy to handle and inexpensive. To provide.

[0010]

In order to achieve the above object, the invention according to claim 1 provides a piezoelectric plate having an input electrode and an output electrode formed thereon, and a plurality of terminal electrodes on which the piezoelectric plate is mounted. A support member having a substrate on which is formed and an external input / output terminal connected to the terminal electrode, the input electrode or the output electrode and the terminal electrode being connected by a connecting member, and the piezoelectric plate having flexibility. Is supported and fixed to the substrate with the piezoelectric plate, the supporting member and the substrate covered with an exterior resin, a cavity is formed in the periphery of the piezoelectric plate except for the portion where the supporting member is attached, and the external terminal is It is characterized in that it is drawn from the exterior resin.

The invention according to claim 2 is the invention according to claim 1, characterized in that the support member having flexibility is attached to a position corresponding to a node point of the piezoelectric plate. .

According to the above structure, the substrate and the lead terminal are partially covered and fixed with the exterior resin, and the piezoelectric plate is supported and fixed to the substrate by the flexible supporting member and the periphery of the piezoelectric plate is supported. Since the cavity is formed in the portion other than the member, stable and reliable support can be obtained and the piezoelectric plate can be isolated from the outside without suppressing the vibration.

Further, since it has a coating structure with an exterior resin, it can be manufactured easily and at low cost.

Further, by supporting the piezoelectric plate on the substrate at the position corresponding to the node point, the suppression of vibration can be further reduced.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the drawings showing embodiments thereof. In the following drawings, the same reference numerals are given to those described in the related art and the description thereof will be omitted.

The structure of the piezoelectric transformer according to the first embodiment of the present invention is shown in FIGS. 1 is an external perspective view, FIG. 2 is a top view of FIG. 1, and FIG. 3 is a sectional view taken along line XX of FIG. 1 and 2, the exterior resin is omitted.

In the piezoelectric transformer of the present embodiment, as shown in FIGS. 1 to 3, the entire one main surface of the piezoelectric plate 1 is adhered onto the substrate 10 by a supporting member 21 having flexibility, and the piezoelectric plate 1 is supported. It is constituted by covering the member 21, the substrate 10 and the cavity 24 with an exterior resin 23. Input electrodes 2a, 2b
Is also formed by extending the end surface of the piezoelectric plate 1.

Terminal electrodes 12a are provided on the periphery of the substrate 10,
12b, 13 are formed, and the input electrodes 2a, 2b,
The output electrode 3 and the terminal electrodes 12a, 12b, 13 are connected to each other by a lead wire 6 as a connecting member. Lead terminals 15 as external terminals are soldered and connected to the terminal electrodes 12a, 12b, 13 respectively, and each lead terminal 15 is drawn out from the exterior resin 23. Although two lead terminals 15 are connected to the terminal electrode 12b that serves as a common end (ground) for input and output, it is needless to say that the number may be one.

The piezoelectric transformer of this embodiment uses the fundamental vibration mode, and the lead wire 6 is formed on the end surface of the piezoelectric plate 1 corresponding to the node point in the lengthwise direction at the substantially central portion thereof.
It is attached to 2b.

As the substrate 10, a resin printed circuit board or a ceramic substrate such as alumina is used.

The supporting member 21 is made of a flexible material having elasticity such as a gel-like silicone adhesive or a gel-like epoxy adhesive which keeps a gel state even after curing.

The exterior resin 23 is for isolating the piezoelectric plate 1 from the outside and protecting the piezoelectric plate 1 from shocks and moisture applied from the outside, and is made of a material having high mechanical strength such as epoxy resin. It is formed by a method such as dipping.

As shown in FIG. 4, the cavity 24 is formed by the piezoelectric plate 1.
The cavity forming agent 22 such as wax is applied to a portion other than the portion where the supporting member 21 is attached, and after dipping the exterior resin 23 so as to cover the supporting member 21, the cavity forming agent 22 and the substrate 10, It is formed by baking and curing at a temperature of 100 to 200 ° C. That is, the cavity forming agent 22 is melted and sublimated when the exterior resin 23 is baked and cured, and is absorbed by the exterior resin 23, and the cavity 24 is formed in the portion where the cavity forming agent 22 is attached.

In this structure, the substrate and a part of the lead terminal are covered and fixed with the exterior resin, and the piezoelectric plate is supported and fixed to the substrate by a flexible supporting member and the periphery of the piezoelectric plate is supported. A cavity is formed in the portion other than the member, so that stable and reliable support is obtained and the piezoelectric plate is isolated from the outside without suppressing the vibration.

Therefore, the piezoelectric plate can be a component which is housed in the exterior resin and is easy to handle.
It is possible to obtain good characteristics in which the deterioration in characteristics such as the boost ratio is greatly reduced.

Further, the exterior resin can be formed by a simple method such as dipping, and the material cost and the manufacturing cost thereof can be significantly reduced as compared with, for example, the method of housing in a case and the structure.

In the present embodiment, a single-plate piezoelectric transformer is shown and described, but a multilayer piezoelectric plate may be used and a similar structure may be used in a laminated piezoelectric transformer in which the input electrodes of the respective layers are alternately connected at the end faces. Of course.

Next, Table 1 shows the measurement result of the boosting ratio in the free state where only the piezoelectric plate was placed on the sponge and the above configuration. Table 1 shows the step-up ratio in the basic (primary) vibration mode of the piezoelectric transformer having a laminated structure of 17 layers, and the load resistance is 10
It is an experimental result when MΩ and 100 KΩ. The resonance frequency is set to about 100 kHz and the supporting member has a thickness of 1
mm-0.5 mm, using a gel-like silicone rubber with a penetration of about 100

[0029]

[Table 1]

As shown in Table 1, in the piezoelectric transformer having the above structure, the step-up ratio is 2 dB lower at any load resistance, as compared with a piezoelectric plate placed only on a sponge. Vibration suppression is significantly reduced.

Next, FIG. 5 shows a sectional view of a piezoelectric transformer using the secondary vibration mode according to the second embodiment of the present invention.

In the piezoelectric transformer of the present embodiment, as shown in FIG. 5, the piezoelectric plate 1 is supported and fixed to the substrate 10 by the supporting members 21 at two points corresponding to the node points in the lengthwise direction. A cavity 24 is also formed in a portion between 10 and except the supporting member 21. Although not shown, the lead wire on the input side is connected to the end faces of the input electrodes 2a and 2b at positions corresponding to the node points that are substantially central portions in the length direction.
The configuration other than the above is the same as that described in the first embodiment, and the description thereof is omitted.

In this structure, the supporting member 21 is provided only at the position corresponding to the node point of the piezoelectric plate 1,
Moreover, since the cavity 24 is increased in number, the suppression of vibration of the piezoelectric plate 1 is further reduced, and a larger boost ratio can be obtained.

Further, the support is performed at a position corresponding to the node point, and as the support member, not only the gel adhesive but also a low-hardness silicone-based or epoxy-based resin adhesive or a low-hardness silicone rubber is molded. Goods can also be used.
Further, this configuration can be applied to a vibration mode of the third order or higher.

In each of the above embodiments, if the connecting member connected to the output electrode is a film-shaped conductor, the suppression of vibration can be further reduced. Further, in each of the above embodiments, the output electrode is disposed on the end face. Although it has been described that it is formed, it may be formed in a band shape in the vicinity of the output side end portion. In the second and higher vibration modes, the output electrode is λ / 4 from the output end.
If it is formed in a band shape at a position corresponding to the node point of, all the supports and all electrical connections of the piezoelectric plate can be set at the positions corresponding to the node point, and more stable support can be obtained.

[0036]

As described above, according to the piezoelectric transformer of the present invention, the piezoelectric plate, which is the main body of the piezoelectric transformer, is supported and fixed to the substrate by the flexible supporting member and is housed inside the exterior resin. Since a cavity is formed in the part other than the support member around the plate, it can be a part that is easy to handle, and the suppression of vibration is greatly reduced.
It is possible to obtain good characteristics such as a boosting ratio with little deterioration in characteristics.

Further, since it has a coating structure with an exterior resin, it can be manufactured easily and at low cost.

Further, by supporting the piezoelectric plate on the substrate at a position corresponding to the node point, the suppression of vibration can be further reduced.

[Brief description of the drawings]

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

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

3 is a cross-sectional view taken along the line XX of the piezoelectric transformer shown in FIG.

FIG. 4 is a sectional view of the piezoelectric transformer according to the first embodiment of the present invention before forming a cavity.

FIG. 5 is a sectional view of a piezoelectric transformer according to a second embodiment of the present invention.

FIG. 6 is a diagram illustrating a basic configuration of a general piezoelectric transformer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric plate 2a, 2b Input electrode 3 Output electrode 6 Lead wire 10 Substrate 12a, 12b, 13 Terminal electrode 15 Lead terminal 21 Support member 22 Cavity forming agent 23 Exterior resin 24 Cavity

Claims (2)

[Claims] 1. A piezoelectric plate on which an input electrode and an output electrode are formed, a substrate on which the piezoelectric plate is mounted and a plurality of terminal electrodes are formed, and an external input / output terminal connected to the terminal electrode. The input electrode or output electrode and the terminal electrode are connected by a connecting member, the piezoelectric plate is supported and fixed to the substrate by a supporting member having flexibility, and the piezoelectric plate, the supporting member and the substrate are packaged. A piezoelectric transformer, which is covered with a resin, has a cavity formed around the piezoelectric plate except a portion where the supporting member is attached, and the external terminal is drawn out from the exterior resin. 2. The piezoelectric transformer according to claim 1, wherein the supporting member having flexibility is attached to a position corresponding to a node point of the piezoelectric plate.