JP2000188433A - Piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric transformer which permit practical operation of a drive circuit at a lower drive frequency and is provided with an effective measure for heat generation. SOLUTION: A piezoelectric transformer 100 is composed of a plurality of internal electrodes 111, a piezoelectric ceramic layer 112 which are alternately laminated, and a laminated layer material 113 in which the adjacent piezoelectric ceramic layer 112 is inversely polarized in the thickness direction. Moreover, the low impedance part 120 and high impedance part 130 are arranged in the thickness direction of the laminated material 113. In this piezoelectric transformer 100, a structure is provided so that the vibration mode is provided to realize vibration to curve toward the end edge side from the center in the plane direction of the laminated material 113, and a plurality of grooves 140 is formed along the plane direction in the side surface orthogonal to the plane direction of the laminated material 113.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer, and more particularly, to a piezoelectric transformer used for a small-sized rectified power supply which is required to be reduced in size, weight and high reliability.

[0002]

2. Description of the Related Art Conventionally, a winding type electromagnetic transformer has been used as a step-down type transformer of a so-called AC adapter for supplying power from a commercial power supply to various battery-driven electronic devices. This electromagnetic transformer has a structure in which a conductive wire is wound around a magnetic core, and it has been very difficult to realize a small and lightweight electromagnetic transformer.

On the other hand, a piezoelectric transformer using a piezoelectric effect, which has a completely different operation principle from an electromagnetic transformer, has been proposed (for example, CA Rosen (CA Ro)).
sen), "Piezoelectric transformer" (Ceram)
ic Transformer), proceedings
Of Electronic Components Symposium 1957 (Proc. Of Electronic C
component symposium (195
7)), pages 256 to 211).

FIG. 5 is a perspective view showing an example of a Rosen type piezoelectric transformer which is a typical piezoelectric transformer. The configuration will be described with reference to FIG. 5. A long plate-shaped piezoelectric ceramic (porcelain) plate 310 extends in the length direction and includes a driving section (low impedance section) 31 and a power generation section (high impedance section) 32.
And is divided into two. The drive unit 31 is polarized in the thickness direction of the piezoelectric ceramic plate 310, and flat electrodes 311 and 312 (312 are formed opposite to 311 and not shown) on both upper and lower surfaces are provided to extend over the entire area of the drive unit. ing. The power generation section 32 is polarized in the length direction of the piezoelectric ceramic plate 310, and an end face electrode 315 is provided on an end face perpendicular to the length axis.

The piezoelectric transformer having this configuration is used for boosting. The operation principle of the piezoelectric transformer will be described. For the boosting, the piezoelectric transformer is disposed between the upper and lower two planar electrodes 311 and 312 of the drive unit 31, ie, the input terminals 317 and 318 are connected. An AC voltage is applied from the outside in between. The drive unit 31 responds to the AC input voltage
It vibrates in the length direction due to the lateral piezoelectric effect. As a result, the piezoelectric ceramic plate 310 vibrates in the longitudinal direction, and the power generation unit 3
2 has a problem between the planar electrode 311 or 312 of the drive section and the end face electrode 315 of the power generation section (in the case of FIG. 5, between the electrode 312 and the electrode 315) due to the piezoelectric longitudinal effect due to the vibration.
That is, a boosted voltage having the same frequency as the input voltage is generated between the output terminals 318 and 319.

If the frequency of the AC input voltage is made equal to the frequency of mechanical resonance in the length direction of the piezoelectric ceramic plate 310, a very high output voltage can be obtained. The transformer shown in FIG. 5 is a transformer that drives the resonance in the first mode, that is, L = 1 (λ / 2), where L is the length of the piezoelectric ceramic plate 310 and λ is the wavelength of the AC input voltage. . Since the Rosen-type piezoelectric transformer described above is a step-up type, if the input and output are reversed, it becomes a step-down type.However, when this is used as a step-down type, there is a problem of impedance matching. , Not practical.

On the other hand, there is a step-down type piezoelectric transformer proposed in Japanese Patent Application Laid-Open No. Hei 4-291773. FIG. 6 shows a configuration of a step-down type piezoelectric transformer proposed in Japanese Patent Application Laid-Open No. 4-291773. In FIG. 6, a portion indicated by 41 is a driving portion (high impedance portion), in which internal electrodes 406 and 407 (407 are not shown) and a piezoelectric ceramic 408 are laminated, and each internal electrode is connected to external electric terminals 404 and 405 ( (Not shown). These piezoelectric ceramics 408 are polarized in the thickness direction. The portion indicated by 42 is a power generation portion (low impedance portion), and the internal electrodes 401, 4
02 and the piezoelectric ceramic 403 are laminated, and the respective internal electrodes are electrically connected via external electric terminals 409 and 410 (not shown). These piezoelectric ceramics 403 are also polarized in the thickness direction. Further, a groove 411 is formed on the contour.

The piezoelectric transformer generates vibration in the thickness direction of the power generation unit 42 in conjunction with vertical vibration in the thickness direction of the drive unit 41 to generate a stepped-down voltage. An AC voltage having a primary or secondary resonance frequency in the thickness direction is applied to the drive unit 41 via the external electric terminals 404 and 405, and the external electric terminals 409 and 41 of the power generation unit 42 are applied.
0 generates a stepped-down voltage in the power generation unit 42. Further, in the piezoelectric transformer of this conventional example, a groove 411 is formed on the contour for the purpose of reducing stress concentration during driving.

[0009]

However, the conventional piezoelectric transformer has the following problems. First, the conventional Rosen-type piezoelectric transformer is a step-up type as described above, and if the input and output are reversed, it becomes a step-down type in principle, but there are problems in terms of impedance matching and conversion efficiency. , Not practical.

Next, the piezoelectric transformer proposed in Japanese Patent Application Laid-Open No. Hei 4-291773 uses thickness longitudinal vibration, and has a driving frequency of 5 to 20 MHz, which is too high, and thus has a difficulty in a driving circuit. Yes, there is a problem in practical application.

Further, since the groove is formed in a direction perpendicular to the vibration direction, the groove is in a peeling direction, and there is a problem in durability against repeated vibration.

Furthermore, when a piezoelectric transformer is used for step-down, heat generation of the piezoelectric transformer due to the flow of a large current is one of the major problems. However, the above-mentioned conventional example does not consider it at all.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its first object to provide a piezoelectric transformer having a low driving frequency and having no problem in practical use of a driving circuit and the like. Second, it is an object of the present invention to provide a piezoelectric transformer in which effective measures against heat generation are taken.

[0014]

According to a first aspect of the present invention, there is provided a piezoelectric transformer in which a plurality of internal electrodes and piezoelectric ceramic layers are alternately laminated, and the piezoelectric ceramic layers adjacent to each other are arranged in the thickness direction. In a piezoelectric transformer, which is composed of a laminate that is polarized in mutually opposite directions, and a low impedance portion and a high impedance portion are arranged in the thickness direction of the laminate, from the center side in the plane direction of the laminate. The configuration has a vibration mode that vibrates so as to bend toward the edge.

According to the invention having such a configuration, unlike the conventional laminated type piezoelectric transformer, the laminated body is formed, for example, as a flat plate-shaped square, so that the laminated body is moved from the center in the surface direction to the edge. Vibrates to bend. Such a vibration mode has a low resonance frequency, and therefore can reduce the driving frequency.

The piezoelectric transformer according to the second aspect is the first aspect of the invention.
The above-described piezoelectric transformer has a configuration in which a plurality of grooves are formed along a surface direction on a side surface orthogonal to a surface direction of the laminate.

According to the invention having such a configuration, the side face of the laminated body vibrates in a direction perpendicular to the direction in which the groove is formed by the vibration in the vibration mode, so that the groove is in a state of fanning the air. Vibrates and cools the sides of the laminate. As a result, heat generation of the piezoelectric transformer can be suppressed by the air cooling effect.

A third aspect of the present invention provides a piezoelectric transformer.
In the piezoelectric transformer described above, a fin portion is provided in the groove along a surface direction. According to the invention having such a configuration, due to the vibration of the fin portion, the air cooling effect becomes more effective, and the heat generation of the piezoelectric transformer can be suppressed.

According to a fourth aspect of the present invention, there is provided a piezoelectric transformer.
3. The piezoelectric transformer according to claim 1, wherein the fin portion has a width of one.
It is configured to have a height of 10 to 10 times. According to the invention having such a configuration, since the fin portion has such a thin structure, an effect of fanning air by vibration is promoted, an air cooling effect is promoted, and heat generation of the piezoelectric transformer can be suppressed.

According to a fifth aspect of the present invention, there is provided a piezoelectric transformer.
5. The piezoelectric transformer according to any one of items 1 to 4, wherein the laminate is a flat square. According to the invention having such a configuration, it is possible to realize a vibration mode in which the stacked body vibrates so as to bend from the center in the surface direction toward the edge.

According to a sixth aspect of the present invention, there is provided a piezoelectric transformer.
5. The piezoelectric transformer according to any one of items 1 to 4, wherein the laminated body has a disk shape. According to the invention having such a configuration, it is possible to realize a vibration mode in which the stacked body vibrates so as to bend from the center in the surface direction toward the edge.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the piezoelectric transformer according to the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the piezoelectric transformer according to the present invention.
Is a perspective view, (b) is a top view, and (c) is a bottom view.

This piezoelectric transformer 100 has an internal electrode 11
1 and a laminated body 113 in which piezoelectric ceramic layers 112 are alternately laminated. The stacked body 113 is a flat square. The upper half of the laminate 113 in the thickness direction in the drawing is configured as a low impedance section (power generation section) 120 and the lower half is configured as a high impedance section (drive section) 130.

The internal electrode 111 of the low impedance section 120 of the piezoelectric transformer 100 shown in FIG.
3, two output electrodes 121 formed on the surface are connected. Further, the internal electrode 111 of the high impedance portion 130 has
One input electrode 131 is connected.

A plurality of grooves 140 are formed on the side surface of the piezoelectric transformer 100 on the side orthogonal to the surface direction.
Are formed on the entire four side surfaces of the laminate 130.

An enlarged view of the groove 140 is shown in FIG. Two grooves 140 are formed on the side surface of the piezoelectric ceramic layer 112 between the internal electrodes 111 at a depth of, for example, about 50 to 300 μm at intervals of about several tens of μm in parallel with the plane direction using, for example, a wire saw. In addition, a fin 141 having a width of about several tens μm is provided between these grooves 140. The fin 141 is preferably a thin plate having a height of 1 to 10 times the width.

FIG. 3 shows a sectional structure of the piezoelectric transformer 100.
Shown in Internal electrode 111 of low impedance section 120
Are alternately connected to the two output electrodes 121 on the left and right, and the internal electrodes 111 of the high impedance section 130 are also connected to the input electrodes 131 every other, although not shown. Piezoelectric ceramic layer 11 of low impedance section 120
2 is the thickness of the piezoelectric ceramic layer 11 of the high impedance portion 130.
2 and the number of stacked low impedance portions 120 is greater than the number of stacked high impedance portions 130. Further, the piezoelectric ceramic layers 112 adjacent via the internal electrodes 111 are polarized in directions opposite to each other in the thickness direction.

The piezoelectric transformer 100 has a flat quadrilateral shape, and has a configuration in which a high impedance section 130 and a low impedance section 120 are separately arranged in the thickness direction. For this reason, when an AC voltage is applied to the input electrode 131, the piezoelectric ceramic layer 112 of the high impedance portion 130 contracts and expands in the plane direction, and thus, as shown in FIG. , In other words, in a mode going outward from the central axis of the quadrilateral. As a result, the fin portion 141 formed in the groove portion 140 bends and vibrates, and vibrates in an operation of fanning air.

That is, by generating the bending vibration as shown by the arrow in the fin portion 141 of the groove portion 140 shown in FIG. 2, the heat generation of the piezoelectric transformer 100 can be suppressed by the air cooling effect, and the energy conversion efficiency can be reduced. It can be improved.

According to such a piezoelectric transformer 100,
By changing the number of layers arbitrarily, it is easy to reduce the impedance in accordance with the impedance matching of the load, and there is no safety problem because the high impedance section and the low impedance section are insulated and separated. As a vibration mode, a mode that is not used conventionally, that is, vibrates so as to bend from the center side in the surface direction toward the edge side, can be driven at a practical drive frequency.

Further, the fin 141 of the groove 140 formed on the side surface of the laminated body 113 is flexibly vibrated in conjunction with this vibration, so that the air cooling effect can be improved and the heat generation of the piezoelectric transformer 100 can be suppressed.

Further, since the groove 140 is formed in the same direction as the vibration, no tensile stress due to the vibration is applied to the groove 140, so that the mechanical reliability against repeated vibration is improved.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment)
An example will be described. The piezoelectric transformer of the present invention was produced by using a green sheet laminating method of the piezoelectric transformer having the configuration shown in FIG. 1 using Nevek 8 (manufactured by Tokin) as a piezoelectric ceramic material. The internal electrode is made of a baked Ag /
Using Pd @ 1st (Ag / Pd ratio is 70/30), screen printing is performed on a green sheet of the piezoelectric ceramic in a predetermined pattern, and then laminated, and the temperature is set to 120 with the piezoelectric ceramic.
It was formed by integrally firing at 0 ° C. and a keeping time of 2 hours.

Here, the PZT-based piezoelectric ceramic and Ag / Pd are used as the material of the piezoelectric ceramic and the internal electrode. However, other combinations of piezoelectric materials having piezoelectricity and electrode materials which can be fired integrally therewith may be used. Needless to say, it works.

As for the lamination structure, the driving section 130 includes seven piezoelectric ceramic layers and six internal electrode layers,
1 is 300 μm, and for the power generation unit 120, 35 layers of piezoelectric ceramics, 34 layers of internal electrode layers,
The thickness between 11 is 100 μm.

Next, after firing, it was processed into a square having a side of 24 mm and a thickness of 6 mm.
A groove 140 having a depth of 150 μm and a width of 50 μm was formed on the side surface, and a fin 141 having a width of 30 μm and a height of 150 μm was formed. Then, after printing the firing type Ag / Pd cost at the position to be the input electrode and the output electrode, firing is performed at a temperature of 700 ° C. and a keeping time of 15 minutes, so that the input electrodes 131 and 131 and the output electrode 121 1
21 was formed.

Then, using a polarization jig, a temperature of 100
An electric field of 2 to 200 ° C. in silicone oil
By applying 3 kV / mm, the driving unit 130 and the power generation unit 12
0 were respectively polarized.

A voltage was applied to the obtained piezoelectric transformer with a load of 10Ω at a driving frequency of 70 kHz, and the transformer was driven in a primary mode of radial resonance. The transformer characteristics were evaluated. Conversion efficiency 9
The conversion ratio was 7% and the conversion ratio was 0.25.

On the other hand, when the groove is not formed, the output power is 20 W and the energy conversion efficiency is 91 to 95%.
Met. This is because the fin 141 of the groove 140 is flexibly vibrated due to driving and is cooled by air, thereby suppressing heat generation. The piezoelectric transformer of the present invention has a higher conversion efficiency than that without the groove. You can see that it is.

(Second Embodiment) Next, a second embodiment of the piezoelectric transformer of the present invention will be described. In the second embodiment, the groove 1 is used.
40 relates to a shape change. In the first embodiment,
The shape of the groove 140 was 150 μm in depth and 50 μm in width, and the width of the fin 141 was 30 μm and the height was 150 μm. In the second embodiment, the depth of the groove 140 was 100 μm.

After the obtained piezoelectric transformer was polarized in the same manner as in the first embodiment, a voltage was applied with a load of 10Ω, and the transformer characteristics were evaluated in the same manner as in the first embodiment. 20W, energy conversion efficiency 98
%, And the metamorphic ratio was 0.25.

In this embodiment, the frequency of the flexural vibration is 1.5 times higher than that of the first embodiment, so that the cooling effect is further improved.

As described above, the piezoelectric transformer of the present invention vibrates in a mode that extends outward from the center axis in the plane direction, which has not existed in the past, and a groove having fins is formed on the side surface of the piezoelectric transformer, thereby forming a piezoelectric transformer. By generating flexural vibration in the fin of the groove in conjunction with the vibration of the transformer and cooling by this, the energy conversion efficiency can be sufficiently increased.
In addition, since the groove is formed in the same direction as the vibration direction, tensile stress due to vibration is not applied to the groove, so that the reliability of mechanical strength due to repeated vibration is improved.

In the above-described embodiments and examples, the shape of the laminated body is a plate-like quadrilateral, but other shapes, for example, a disk-like shape are preferable shapes from the vibration mode, and are limited to quadrilaterals. Not something. Further, the piezoelectric transformer of the present invention can be of a step-up type, and is not limited to a step-down type.

[0045]

As described above, according to the piezoelectric transformer of the present invention, a laminate in which a plurality of internal electrodes and piezoelectric ceramic layers are alternately laminated is formed into, for example, a flat quadrilateral. A piezoelectric transformer having a vibration mode that vibrates so as to bend from the center in the planar direction of the laminate toward the edge can be obtained. Therefore, the impedance can be easily reduced, and the driving can be performed at a practical driving frequency.

Further, by providing a groove on the side surface of the laminated body and providing a fin in the groove, the fin flexes and vibrates in the above vibration mode, so that the cooling effect is excellent and the energy conversion efficiency can be increased. .

[Brief description of the drawings]

1A and 1B show an embodiment of a piezoelectric transformer according to the present invention, wherein FIG. 1A is a perspective view, FIG. 1B is a top view, and FIG. 1C is a bottom view.

FIG. 2 is a sectional view showing a groove of the piezoelectric transformer of the present invention.

FIG. 3 is a sectional view showing a sectional structure of one embodiment of the piezoelectric transformer of the present invention.

FIG. 4 is a schematic diagram showing one of the vibration modes of the piezoelectric transformer of the present invention.

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

FIG. 6 is a perspective view showing a conventional piezoelectric transformer.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 piezoelectric transformer 111 internal electrode 112 piezoelectric ceramic layer 113 laminated body 120 low impedance section (power generation section) 121 output electrode 130 high impedance section (drive section) 131 input electrode 140 groove section 141 fin section

Claims (6)

[Claims] 1. A laminated body in which a plurality of internal electrodes and piezoelectric ceramic layers are alternately laminated, and said piezoelectric ceramic layers adjacent to each other are polarized in directions opposite to each other in a thickness direction. In a piezoelectric transformer in which a low impedance portion and a high impedance portion are arranged in a thickness direction, the piezoelectric transformer has a vibration mode that vibrates so as to bend from a center side in a plane direction of the laminated body toward an edge side. Piezo transformer. 2. The piezoelectric transformer according to claim 1, wherein a plurality of grooves are formed along a surface direction on a side surface orthogonal to a surface direction of the laminated body. 3. The piezoelectric transformer according to claim 2, wherein a fin portion is provided in the groove along a surface direction. 4. The piezoelectric transformer according to claim 3, wherein the fin has a height of 1 to 10 times the width. 5. The piezoelectric transformer according to claim 1, wherein the laminate is a flat square. 6. The piezoelectric transformer according to claim 1, wherein the laminated body has a disk shape.