JPH08130335A - Piezoelectric transformer - Google Patents

Abstract

PURPOSE: To make it possible to mount an output lead wire on the node of vibration, and to prevent the deterioration of characteristics and the lowering of reliability by a method wherein an interdigital electrode is provided on the half surface in longitudinal direction of the rectangular plate formed by piezoelectric ceramic, and this interdigital electrode is used for a ceramic polarization and transformer output. CONSTITUTION: A pair of electrodes 12a and 12b, to be used for ceramic polarization opposing to thickness direction, and transfer input are formed on the surface almost half of the longitudinal direction of the rectangular plate 11 of a PZT piezoelectric ceramic. On the surface of the remaining half in longitudinal direction of the rectangular plate 11, two each and four in total of the first and the second common electrodes 14a (14b) and 16a and three first pectinated electrodes 15a and the second common electrode 16a are connected to the first common electrode 14a in orthogonally intersecting direction, three first pectinated electrode 15a and the second common electrode 16a are connected in longitudinal direction of the rectangular plate 11 in orthogonally intersecting direction in such a manner that an interdigit is formed with the first pectinated electrode 15a, a total of three second pectinated electrode 17a are formed in longitudinal direction of the rectangular plate 11, and interdigital electrodes 10 are arranged.

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 piezoelectric transformer utilizing resonance in a length direction of a rectangular plate made of piezoelectric ceramics.

[0002]

2. Description of the Related Art Conventionally, in a power source used for lighting a static electricity generator or a backlight of a liquid crystal display,
Although it does not require a large current value, a high voltage power source of about 1 KV is used. For these power supplies, electromagnetic transformers are used for boosting, but due to demands such as reduction of electromagnetic noise generated, low power consumption, and small and low profile of equipment, consideration of practical use for voltage transformers is under consideration. Has been done.

FIG. 3 shows the structure of a 1/2 wavelength resonance mode piezoelectric ceramic (piezoelectric vibrator) used in a conventional piezoelectric transformer. In FIG. 3, on a surface (a pair of surfaces) of a rectangular plate 41 made of piezoelectric ceramic, a pair of electrodes 42a and 42b facing each other in the thickness direction are formed on almost half of the surface in the length direction. ing. One of the electrodes 42a and 42b serves as a transformer input side polarization electrode, and the other serves as an input electrode.

Further, an end surface electrode 44 is formed on the end surface of the rectangular plate 41 opposite to the part where the pair of electrodes 42a and 42b are formed. In the rectangular plate 41, the electrodes 42a and 42b are polarized in the thickness direction, and the end face electrodes 44,
The portion between the electrodes 42a and 42b is polarized in the length direction of the rectangular plate 41.

FIGS. 4 (a) to 4 (c) are explanatory views of the operation principle of the piezoelectric transformer of FIG. 3, and show a state in which the rectangular plate 41 is viewed from the side. FIG. 4B is a displacement distribution when the rectangular plate 41 is vibrating in a half-wavelength resonance mode of longitudinal vibration, and the reference numeral 51 shown in the center of the rectangular plate 41 indicates a vibration node. ing. FIG. 4C shows a rectangular plate 4.
1 shows the strain distribution when vibrating in the 1/2 wavelength resonance mode of the longitudinal vibration.

In FIG. 4A, the electrode 42b on one surface of the rectangular plate 41 is used as a ground terminal, and the electrode 42a on the other surface is equal to the resonance frequency of the rectangular plate 41 in the half-wavelength resonance mode in the length direction. Apply voltage of frequency. At this time, the rectangular plate 41 vibrates as shown by the line B in FIG. Here, a voltage is generated between the electrode 42b and the end surface electrode 44 by the piezoelectric effect.

Further, the input voltage applied to the electrode 42a and the output voltage generated at the end face electrode 44 will be described.
The facing distance between the electrodes 42a and 43b is sufficiently smaller than the distance between the electrode 42b and the end surface electrode 44. Since the areas of the electrodes 42a and 42b are sufficiently larger than the area of the end face electrode 44, the capacitance on the input side is sufficiently larger than the capacitance on the output side.

Therefore, when a low voltage is applied to the input side to vibrate and vibrate, the electrodes 42a and 42b on the input side are vibrated.
A large voltage is generated which is proportional to the ratio of the distance between the output side end surface electrode 44 and the output side end surface electrode 44.

As another conventional example, FIG. 5 shows the structure of a ½ wavelength resonance mode piezoelectric ceramic (piezoelectric vibrator) used in a piezoelectric transformer.

The piezoelectric transformer has a pair of electrodes 82a and 82b for ceramics polarization and transformer input, which are opposed to each other in the thickness direction on the surface of the rectangular plate 81 in the approximately half length direction.
have. Interdigital electrodes 80 are formed on at least one surface of the other half of the rectangular plate 81 in the length direction.

The interdigital electrode 80 includes the first and second comb-shaped electrodes 84a and 86a and the first and second common electrode 83.
a and 85a. That is, the interdigital electrode 80 includes the first comb-tooth-shaped electrodes 84a which are arranged in the lengthwise direction and are arranged at a predetermined pitch in a direction orthogonal to the lengthwise direction, and the first combtooth-shaped electrodes 84a. A plurality of second comb-teeth-shaped electrodes 86 in the lengthwise direction so as to form an interdigitated electrode with the electrode 84a.
a is formed. First and second comb-shaped electrodes 84a
And 86a are connected to each other by the first and second common electrodes 83a and 85a which are orthogonal to the longitudinal direction at the surface end of the rectangular plate 81, and the first and second comb-teeth electrodes 84a and 86a are connected to the ceramics. The electrodes are for polarization and transformer output.

The interdigital electrodes 80 are arranged on the other half of the pair of surfaces in the lengthwise direction of the rectangular plate 81, and the interdigital electrodes 80 are also arranged on the opposite surface. In FIG. 5, only the second comb-teeth electrode 86b facing the second comb-teeth electrode 86a in the thickness direction is shown.

The piezoelectric transformer shown in FIG. 5 is also disclosed in, for example, Japanese Patent Laid-Open No. 6-204582. In such a piezoelectric transformer, since the polarization direction on the output side is orthogonal to the length vibration direction of the rectangular plate 81,
The output side forming the cross finger has a piezoelectric lateral effect, and the output voltage is proportional to the electromechanical lightness factor k31 = 0.34.

[0014]

3 and 4 (a).
In the piezoelectric transformer described with reference to FIG. 4C, the piezoelectric transformer shown in FIG.
It is necessary to support the vibrator at the vibration node 51 shown in FIG.

On the other hand, as described above, it is necessary to take out the output voltage from the end face electrode 44 having the largest vibration amplitude, and the characteristics of the vibrator change due to the addition of the mass due to the attachment of the lead wire, or the lead wire take-out portion due to the vibration. There is a problem that characteristics such as step lines and the like as a piezoelectric transformer are deteriorated and reliability is lowered.

Therefore, a special treatment process such as using a material having a small influence on vibration such as conductive rubber for forming the output terminal lead-out portion or forming an electrode having high adhesion with the piezoelectric ceramics as an end face electrode is required. Is.

Further, the output voltage of the piezoelectric transformer depends on the above-mentioned distance between the electrodes on the input side and the output side and also depends on the load resistance, so that there is a problem that a large output voltage cannot be obtained.

Further, in the piezoelectric transformer shown in FIG. 5 as another conventional example, the step-up ratio as a transformer is proportional to the width dimension, and therefore a wide structure is required to increase the step-up ratio. .

Therefore, it is an object of the present invention to provide a piezoelectric transformer in which an output lead wire can be attached to a vibration node and which can prevent deterioration of characteristics and deterioration of reliability due to support. .

Another object of the present invention is to easily design a device corresponding to the size of the load resistance by changing the pitch between the electrodes, and to obtain a relatively large output voltage even if the load resistance is small. To provide a transformer.

[0021]

According to the present invention, in the piezoelectric transformer utilizing the resonance mode in the lengthwise direction of the rectangular plate made of piezoelectric ceramics, the lengthwise direction of the rectangular plate is divided into two. A pair of electrodes used for ceramics polarization and a transformer input on the surfaces of one section that face each other in the thickness direction, and intersecting fingers on at least one surface of the other section of the rectangular plate in the length direction. A plurality of common electrodes having electrodes, the crossing finger electrodes facing each other at a predetermined interval, and a plurality of comb-teeth electrodes having one end connected to the common electrode and the other end extending toward the facing common electrode. A piezoelectric transformer in which the comb-teeth electrodes are arranged parallel to each other with a predetermined pitch to form an interdigitated electrode, and the interdigitated electrode is used for ceramic polarization and transformer output. Obtained.

Further, according to the present invention, the interdigital electrodes are formed on at least one surface of the first and second electrodes in parallel with each other at a predetermined interval and in the lengthwise direction of the rectangular plate.
A common electrode and first and second comb-teeth-shaped electrodes arranged at a predetermined pitch in a direction orthogonal to the first and second common electrodes and in a length direction of the rectangular plate, One end of the first comb tooth-shaped electrode is connected to the first common electrode, and one end of the second comb tooth-shaped electrode is connected to the second common electrode. Is obtained.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a piezoelectric transformer of the present invention will be described below with reference to the drawings.

Referring to FIG. 1, the piezoelectric transformer utilizes the resonance mode in the lengthwise direction of the rectangular plate 11 made of piezoelectric ceramics, and the lengthwise direction of the rectangular plate 11 is divided into two. A pair of electrodes 12a and 12b for ceramics polarization and transformer input are provided on a pair of surfaces facing each other in the thickness direction of the section.

At least one surface of the pair of surfaces of the other section of the rectangular plate 11 in the lengthwise direction has at least one surface thereof with the interdigital electrode 1.
0 is formed. The interdigital electrode 10 includes a plurality of first comb-teeth-shaped electrodes 15a and a second comb-teeth-shaped electrode 17a which are alternately formed so as to form an interdigitated finger with a predetermined pitch in parallel with each other, and a plurality of first comb-shaped electrodes. It has a first common electrode 14a in which one ends of the tooth-shaped electrodes 15a are connected to each other, and a second common electrode 16a in which one ends of a plurality of second comb-tooth-shaped electrodes 17a are connected to each other. .

In the piezoelectric transformer shown in FIG. 1, the rectangular plate 11 is used.
Of the first and second common electrodes 14a and 16a, which are long in the length direction, and one end of which is connected to the first common electrode 14a, and the length of the rectangular plate 11 A plurality of first comb-teeth-shaped electrodes 15a arranged at a predetermined pitch in the vertical direction, and orthogonal to the second common electrode 16a so as to form an interdigitated finger with the first comb-teeth-shaped electrodes 15a. And a plurality of second comb-teeth-shaped electrodes 17a arranged in a predetermined pitch in the length direction of the rectangular plate 11. The interdigital electrodes 10 are electrodes for ceramics polarization and transformer output.

The interdigital electrodes 10 are arranged on a pair of surfaces of the rectangular plate 11 which face each other in the thickness direction of the rectangular plate 11.
In the figure, only the first common electrode 14b facing the first common electrode 14a in the thickness direction is shown on the opposite surface.

Generally, it is desirable to support the piezoelectric transformer at the nodes of vibration so as not to reduce the electromechanical coupling coefficient (Q) or change the resonance frequency, but the actual support is not always easy.

In the piezoelectric transformer of the present invention, when the rectangular plate 11 is driven in the longitudinal direction in the nth-order resonance mode, on the input side, approximately half the surface of the rectangular plate 11 in the longitudinal direction is formed, and in the thickness direction. There is a vibration node on the fixed side on the opposing ceramic polarization and transformer input electrodes. Further, on the output side, the first and second common electrodes 14a and 1a in the length direction are provided.
6a and the first and second comb-teeth-shaped electrodes 15a and 17a are present, and the first and second common electrodes 14a and 16a and the first
There are vibration nodes on the second comb-shaped electrodes 15a and 17a.

Therefore, in the piezoelectric transformer of the present invention, the electrode can be taken out from the vibration node, and the piezoelectric transformer is supported so that the electromechanical coupling coefficient (Q) does not decrease and the resonance frequency does not change. Is also possible.

Further, the capacitance on the output voltage side of the piezoelectric transformer can be made larger than that of the conventional piezoelectric transformer because the electrodes on the output side form interdigitating fingers, and the output of the piezoelectric transformer can be increased. It is possible to reduce the load resistance dependency of the voltage.

More specifically, the piezoelectric transformer shown in FIG. 1 has a length of PZT-based piezoelectric ceramics of 4 mm.
A 1-wavelength resonance mode voltage transformer was prototyped using a rectangular plate 11 having a width of 0 mm, a width of 10 mm, and a thickness of 1 mm. The displacement vibration mode of the piezoelectric transformer is shown in FIG.

In FIG. 1, the length of the rectangular plate 11 is 40 mm.
Of the electrodes 12a and 1 for ceramics polarization and transformer input, which face each other in the thickness direction, on almost half the surface in the length direction of the
A pair of 2b is formed. On the pair of surfaces of the remaining half of the rectangular plate 11 in the length direction, two first and second common electrodes 14a (14b) each having a width of 1.0 mm and a length of 18 mm are formed on each of the two surfaces in the length direction. ) And 16a and the first common electrode 13a connected in a direction orthogonal to the rectangular plate 11.
A total of three first comb-teeth-shaped electrodes 15a on one surface having a pitch of 5 mm and a width of 0.5 mm, and a second comb in the lengthwise direction so as to form cross fingers with the first comb-teeth-shaped electrodes 15a. Common electrode 1
6a in the direction orthogonal to the rectangular plate 11, and in the lengthwise direction of the rectangular plate 11.
A total of three second comb tooth-shaped electrodes 17a are formed on one surface having a pitch of 5 mm and a width of 1.5 mm, and the interdigital electrodes 10 are arranged. For the interdigital electrode 10, a piezoelectric transformer having ceramics polarization and transformer output electrodes was prototyped.

The polarization of the piezoelectric transformer was carried out at a temperature of 150 ° C. and an electrolytic strength of 1.2 KV / mm. Table 1 shows the measurement results of the boost ratio between the input voltage and the output voltage of the piezoelectric transformer and the load resistance (Ω) of the output. In Table 1, the measurement result of the example is shown as Example 1, and the measurement result of the piezoelectric transformer having the conventional structure shown in FIG. 3 is shown as a comparative example.

[0035]

[Table 1]

As is apparent from Table 1, in the piezoelectric transformer of the present invention, the electrode structure on the output side is the cross finger electrode 10, so that the piezoelectric transformer having the conventional structure in the low load resistance range of about 1 MΩ or less. Greater boost is obtained.

FIGS. 2A to 2C are explanatory views of the operation principle of the piezoelectric transformer using the piezoelectric vibrator of FIG.
2A to 2C show side surfaces of the rectangular plate 11. In FIG. 2B, the rectangular plate 11 has a longitudinal vibration of 1
It is the displacement distribution when vibrating in the wavelength resonance mode,
Reference numeral 21 indicates a vibration node. FIG. 2C shows the strain distribution when the rectangular plate 11 is vibrating in the one-wavelength resonance mode of longitudinal vibration.

In FIG. 2A, one electrode 12b is used as a ground terminal, and a voltage having a frequency equal to the resonance frequency of the lengthwise one-wavelength resonance mode of the rectangular plate 11 is applied to the other electrode 12a. At this time, the rectangular plate 11 is changed to A in FIG.
Vibrate as shown by the line.

The piezoelectric transformer is supported by vibrating nodes 21 because there are two nodes of one-wavelength resonance mode in the longitudinal direction of the rectangular plate 11.

In such a piezoelectric transformer, since the polarization direction on the output side is parallel to the length vibration direction of the rectangular plate 11, the output side forming the crossing finger has a piezoelectric vertical effect, and the output voltage is electromechanically coupled. It is proportional to the coefficient k33 = 0.67.
That is, with this piezoelectric transformer, it is possible to form a transformer having an elongated structure with a width narrower than that of the conventional piezoelectric transformer shown in FIG.

[0041]

As described above with reference to the embodiments, according to the piezoelectric transformer of the present invention, since the interdigitated electrodes are formed on the surface of almost half of the rectangular plate, the output lead wire can be attached to the node of vibration. This is possible, and it is possible to prevent deterioration of characteristics and deterioration of reliability due to support.

Further, by changing the electrode pitch of the interdigital electrodes, the design corresponding to the size of the load resistance can be facilitated, and a piezoelectric transformer which can obtain a relatively large output voltage even if the load resistance is small can be provided.

Further, since the step-up ratio of the transformer is proportional to the length dimension, it is possible to form a narrow transformer having a narrow width.

[Brief description of drawings]

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

2A is a sectional view of a piezoelectric ceramic rectangular plate, FIG.
(B) shows a displacement distribution when the piezoelectric ceramic rectangular plate is vibrating in a longitudinal one-wavelength resonance mode, and (c) shows a strain distribution at that time.

FIG. 3 is a perspective view of a conventional ½ wavelength resonance mode piezoelectric ceramic.

4A is a sectional view of a piezoelectric ceramic rectangular plate, FIG.
(B) shows a displacement distribution when the piezoelectric ceramic rectangular plate is vibrating in a longitudinal one-wavelength resonance mode, and (c) shows a strain distribution at that time.

FIG. 5 is a perspective view of a conventional 1/2 wavelength resonance mode piezoelectric ceramics.

[Explanation of symbols]

11, 41, 81 rectangular plate 12a, 12b, 42a, 42b, 82a, 82b
Electrodes 14a, 14b, 83a First common electrodes 16a, 85a, Second common electrodes 15a, 84a, First comb-shaped electrodes 17a, 86a, 86b Second comb-shaped electrodes 10, 80 Interdigital electrode 21 , 51 Vibration nodes 44 End electrodes

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsunori Kumasaka 6-7 Koriyama, Taichiro-ku, Sendai-shi, Miyagi Tokin Co., Ltd.

Claims (2)

[Claims] 1. A piezoelectric transformer using a resonance mode in the lengthwise direction of a rectangular plate made of piezoelectric ceramics, wherein the rectangular plate is divided into two lengthwise directions, and one of the sections is made to have a relative thickness direction. A pair of electrodes used for ceramics polarization and a transformer input is provided on the facing surface, and a crossing finger electrode is provided on at least one surface of the other section in the lengthwise direction of the rectangular plate. It has a plurality of common electrodes facing each other at a predetermined interval, and a plurality of comb-teeth electrodes having one end connected to the common electrode and the other end extending toward the common electrode facing each other. A piezoelectric transformer, which is arranged in parallel to form an interdigitated finger with a predetermined pitch, and uses the interdigitated electrode for ceramic polarization and transformer output. 2. The piezoelectric transformer according to claim 1, wherein
The interdigital electrodes are formed on at least one of the surfaces in parallel to each other at a predetermined interval and in the lengthwise direction of the rectangular plate, and the first and second common electrodes and the first and second common electrodes. The first and second comb-teeth-shaped electrodes arranged at a predetermined pitch in a direction orthogonal to each other and in the lengthwise direction of the rectangular plate, and one end of the first comb-teeth-shaped electrode has the first common shape. A piezoelectric transformer, wherein the piezoelectric transformer is connected to an electrode, and one end of the second comb-shaped electrode is connected to the second common electrode.