JP2904091B2 - Piezoelectric transformer element - Google Patents

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 various high-voltage power supplies, and more particularly, to a small-sized piezoelectric transformer element which requires high miniaturization and high reliability.

[0002]

2. Description of the Related Art Conventionally, in a power supply circuit in a device requiring a high voltage, such as a deflection device of a television or a charging device of a copying machine, a winding type electromagnetic transformer has been used as a transformer for generating a high voltage. . This electromagnetic transformer has a structure in which a conductor is wound around a core of a magnetic material, and it is necessary to increase the number of conductors to be wound in order to realize a high denaturation ratio. For this reason, it has been very difficult to realize a small electromagnetic transformer.

On the other hand, a piezoelectric transformer using a piezoelectric effect has been proposed. This piezoelectric transformer will be described with reference to FIG. FIG. 2 shows a conventional piezoelectric transformer.
It is a perspective view showing the structure of (Rosen tertiary type piezoelectric transformer).

As shown in FIG. 2, a conventional Rosen tertiary type piezoelectric transformer has a rectangular piezoelectric ceramics 210 provided with electrodes on its surface. And a planar electrode 212, 213, 214, 215 (note that 213 and 215)
Are formed facing the opposite surfaces of 212 and 214, not shown in FIG. 2), and this portion is polarized in the thickness direction.

[0005] Similarly, the portion indicated by 22 is "high impedance".
It is the power generation section of the dance, and has strip electrodes 216 and 217 (217
Is formed facing the opposite surface of the piezoelectric plate 216 and is not shown in FIG. 2), and this portion is polarized in the length direction of the piezoelectric plate. When the conventional piezoelectric transformer is driven by applying an AC voltage between the external electric terminals 218 and 219, a voltage is generated between the external electric terminals 218 and 220.

On the other hand, as a method for improving the strength of a piezoelectric ceramic sintered body, there is a method disclosed in, for example, Japanese Patent Application Laid-Open No. 4-171990. According to this conventional method, vitreous is added to the entire piezoelectric ceramic to improve the strength.

[0007]

The first problem with the configuration of the conventional Rosen tertiary type piezoelectric transformer is that when the vibration speed is increased, the rectangular electrodes 216, In other words, cracks occur in the piezoelectric ceramics near 217 (see FIG. 2 described above), leading to cracks. The reason will be described with reference to FIG. FIGS. 3A and 3B are diagrams illustrating the problems of the conventional piezoelectric transformer, in which FIG. 3A is a cross-sectional view of the piezoelectric transformer, and FIG. 3B is a diagram illustrating a stress distribution when the piezoelectric transformer vibrates. . [31 in FIG. 3 (A)
Reference numerals 6 and 317 correspond to the strip electrodes 216 and 217 in FIG. ]

In a conventional Rosen tertiary piezoelectric transformer,
As shown in FIG. 3 (B), internal stress in the longitudinal direction due to polarization
310 and stress 311 at the time of vibration are combined to form a total stress 31 at the time of vibration.
2 (including the internal stress in the length direction due to polarization)
When the maximum tensile stress 313 acts on the piezoelectric ceramic portion near the electrodes 316 and 317 of the power generation section (see FIG. 3 (A)) and the vibration speed of the piezoelectric transformer increases, the tensile stress 313 increases the tensile force of the piezoelectric ceramic base. The stress will be exceeded. For this reason, in the conventional Rosen tertiary type piezoelectric transformer, as described above, there is a problem that cracks occur in the piezoelectric ceramics near the electrodes 316 and 317 of the power generation unit and cracks occur (first problem). point).

A second problem with the conventional Rosen tertiary type piezoelectric transformer is that glassy material is added to the entire piezoelectric ceramics in order to improve the strength of the piezoelectric ceramics. This means that a problem occurs in the characteristics of the piezoelectric transformer, such as a change in vibration speed and occurrence of vibration inhibition. The reason is that vitreous is added to the entire piezoelectric ceramic.

The present invention improves the strength of a portion of a piezoelectric ceramic to which a maximum tensile force is applied without affecting vibration by adding vitreous material only to the piezoelectric ceramic near an electrode of a power generation unit. It is an object of the present invention to provide a piezoelectric transformer element in which cracks do not occur in the piezoelectric ceramics even when the vibration speed of the piezoelectric ceramic is increased, and a transformer characteristic higher than that of the conventional one can be obtained.

[0011]

The present invention does not add vitreous to the entire piezoelectric ceramic as in the above-mentioned conventional method, but rather employs a piezoelectric ceramic sandwiched between opposing strip electrodes.
The present invention is characterized in that vitreous is added to the ceramics and piezoelectric ceramics in the vicinity thereof, thereby providing the above-described piezoelectric transformer element of the present invention.

That is, the piezoelectric transformer element of the present invention is composed of opposing planar electrodes formed on the main surface at both ends in the longitudinal direction of the long plate-shaped piezoelectric body, and is polarized in the thickness direction. Two driving parts, and a portion sandwiched between the two driving parts,
In a piezoelectric transformer having an opposing strip-shaped electrode formed on the main surface and a power generation unit polarized in the longitudinal direction between the planar electrodes, a piezoelectric ceramic narrowed by the opposing strip-shaped electrode; Piezoelectric ceramic in the vicinity
A piezoelectric transformer element characterized in that vitreous is added to ceramics . (Claim 1).

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. In the present invention, PbO, Zn
_{O, SiO 2, Al 2 O} 3, B 2 O 3, BaO, Li 2 O, is preferably one comprising at least one or more of Bi ₂ O _3, also the addition ratio of such glassy 0.5 5 wt% is preferred. When the glassy content is less than 0.5 wt%, cracks are observed. On the other hand, when it exceeds 5 wt%, cracks are not observed, but the transformer characteristics are slightly lowered.

[0014]

The strength of ceramics is basically governed by the strength at the grain boundaries of the ceramic material. Therefore, in order to improve the strength of the ceramic, it is necessary to improve the strength of the ceramic material at the grain boundaries. One of the means is to add vitreous to ceramics to improve the strength at grain boundaries.

In view of the above, conventionally, vitreous has been added to the entire ceramic to improve the strength of the entire ceramic. However, when this is applied to the piezoelectric transformer as it is, the vibration of the piezoelectric transformer is affected. There is a problem that the transformer characteristics deteriorate.

Therefore, the present invention is characterized in that the vitreous material is added only to the ceramic portion where cracks occur due to a tensile force acting by vibration so as not to affect the vibration inhibition. In this case, it is possible to improve the strength at the grain boundary of the material of the ceramic portion on which the metal acts most.

[0017]

EXAMPLES Next, the present invention will be described specifically with reference to examples of the present invention. However, the present invention is not limited to the following examples, but falls within the scope of the gist of the present invention. Various modifications and changes are possible.

(Embodiment 1) FIG. 1 shows an embodiment of the present invention.
FIG. 1 is a perspective view of a piezoelectric transformer element showing (Example 1). In FIG. 1, reference numeral 110 denotes a piezoelectric ceramic, 111 denotes a portion to which vitreous is added, and 112, 113, 114, and 115 denote planar electrodes (note that 113 and 115 are formed to face opposite surfaces of 112 and 114, respectively). 1, not shown in FIG. 1), 116 and 117 are strip-shaped electrodes (117 is formed opposite to the opposite surface of 116 and not shown in FIG. 1), and 118, 119 and 120 are external. An electric terminal is shown, 11 is a power generation unit, and 12 is a drive unit.

As a method of driving the piezoelectric transformer according to the first embodiment, an AC voltage is applied between the external electric terminals 118 and 119 of the driving unit 11. Thus, the piezoelectric transverse effect mode via an electromechanical coupling coefficient K ₃₁ - repeatedly occurs distortion in the longitudinal direction on the basis of de, the result, longitudinal vibration in the longitudinal direction across the piezoelectric ceramic is produced. This longitudinal vibration in the length direction propagates to the power generation unit 11, and the electromechanical coupling coefficient K between the external electrode terminals 118-120.
_A voltage is generated via ₃₃ based on the piezoelectric longitudinal effect mode.

Next, the manufacturing method of this embodiment will be described. First, a Zn composition was added to Nepec 8 (manufactured by Tokin) in a batch composition.
O: 57%, B ₂ O ₃ : 25%, SiO ₂ : 10%, Al ₂ O ₃ : 8% Glass powder added with 0.5 wt% of glassy material is 2.0 m long
It is molded to mx 10.0 mm wide x 1.0 mm thick. This is set so as to be the center of the length of the long plate-shaped piezoelectric ceramics 110 composed of the composition of Nepec 8, and the long plate-shaped piezoelectric ceramics 110 is 28.0 mm long × 10.0 mm wide × 1.0 mm thick.
It is molded and processed to a size of mm.

Next, using the Ag or Ag / Pd electrode paste, the flat electrodes 112, 113, 114 and 115 are positioned at the input electrode positions, and the strip electrodes 116 and 117 are positioned at the output electrode positions. It is formed by printing and fired. Then, using a polarization jig, an electric field of 0.5 to 0.7 k in air at a temperature of 300 to 350 ° C.
V / mm is applied, the temperature is lowered to 100 ° C. or less in the applied state, and then the applied electric field is cut off to generate the power generation unit 12.
Polarization. Thereafter, an electric field of 2 to 3 kV / mm is applied in a silicon oil at a temperature of 100 to 200 ° C. to drive the drive unit 11.
Polarization.

When the piezoelectric transformer obtained in the first embodiment was driven by applying a voltage, the vibration speed was 1.2 m / sec.
No cracks were observed up to. Comparing this with the conventional one, the former was 0.9 m / sec, but now 1.2 m / sec, and the transformer characteristics were improved.
In addition, when the amount of addition was less than 0.5 wt% with glass having the same composition, the vibration level (1.0 m / sec.
Cracking was observed in c) (about 10%).

Example 2 Example 2 differs from Example 1 in the vitreous composition and the amount added.
Only this point will be described. In Example 2, the vitreous composition to be added is a batch composition of ZnO: 52% and PbO: 10%.
%, B ₂ O ₃ : 23%, SiO ₂ : 8%, Al ₂ O ₃ : 7%, and the amount of glass added is 1.0 wt%.

When a voltage was applied to the piezoelectric transformer obtained in Example 2 and the piezoelectric transformer was driven, the vibration speed was 1.35 m / sec.
No occurrence of cracks was observed up to, and the transformer characteristics were improved as compared with the conventional one. Also, when the glass content of the same composition was examined with the addition amount exceeding 5.0 wt%,
No cracking was observed, but a slight decrease in transformer characteristics was observed (efficiency decreased from 96% to 93%).

[0025]

According to the present invention, as described in detail above, in a piezoelectric transformer element, vitreous is added to piezoelectric ceramics in the vicinity of a strip-shaped electrode of a power generation unit to partially improve the strength of a piezoelectric body. Thus, even when the vibration speed of the piezoelectric transformer is increased, cracks do not occur in the piezoelectric ceramics, and a remarkable effect that the transformer characteristics are improved is produced.

[Brief description of the drawings]

FIG. 1 is a perspective view of a piezoelectric transformer showing a first embodiment (Embodiment 1) of the present invention.

FIG. 2 is a perspective view showing a conventional piezoelectric transformer.

FIG. 3 is a view for explaining a problem of the conventional piezoelectric transformer, in which (A) is a sectional view of the piezoelectric transformer,
(B) is a diagram showing a stress distribution during piezoelectric transformer vibration.

[Explanation of symbols]

11, 21 Drive unit 12, 22 Power generation unit 110, 210 Piezoelectric ceramic 111 Glass-added portion 112, 114, 212, 214 Planar electrode 116, 216 Strip electrode 118, 119, 120, 218, 219, 220 External Electric terminal 310 Internal stress in the longitudinal direction due to polarization 311 Stress during vibration 312 Total stress during vibration (including internal stress in the longitudinal direction due to polarization) 313 Maximum tensile stress 316, 317 Electrodes of power generation unit

Claims (3)

(57) [Claims] 1. Two driving sections, which are constituted by opposing planar electrodes formed on a main surface at both ends in a length direction of a long plate-shaped piezoelectric body and polarized in a thickness direction, In a portion sandwiched by a driving unit, in a piezoelectric transformer having a power generating unit which is formed in a longitudinal direction and polarized between the opposed strip-shaped electrodes formed on the main surface and the planar electrodes, the opposed strips A piezoelectric transformer element characterized in that vitreous is added to the piezoelectric ceramics narrowed by the electrode and the ceramics of the piezoelectric ceramics near the piezoelectric ceramics . 2. The method according to claim 1, wherein the vitreous material is PbO, ZnO, SiO ₂ , Al.
_2. The piezoelectric transformer element according to claim 1, wherein the piezoelectric transformer element is made of at least one of ₂ O ₃ , B ₂ O ₃ , BaO, Li ₂ O, and Bi ₂ O ₃ . 3. The addition ratio of the vitreous is 0.5 to 5% by weight.
The piezoelectric transformer element according to claim 1, wherein: