JP4160658B2 - Piezoelectric transformer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric transformer mainly used in DC / DC converters and DC / AC inverters of small portable electronic devices and OA devices.
[0002]
[Prior art]
Conventionally, this type of piezoelectric transformer utilizes the inverse piezoelectric effect and piezoelectric effect of a piezoelectric vibration element, converts electrical input into mechanical energy, mechanically excites the piezoelectric vibrator, and then regenerates the mechanical vibration again. It is known as an electronic device that obtains an action such as voltage step-up or step-down by converting it into electrical output.
[0003]
Such a piezoelectric transformer is characterized by having no windings as compared with an existing electromagnetic transformer. The output power P _OUT of the piezoelectric transformer has a relationship of P _OUT = αmv ² k ² f (where α is a coefficient) where f is the driving frequency, m is the mass, v is the vibration speed, and k is the electromechanical coupling coefficient. It is represented by According to such a relational expression, a piezoelectric transformer using various vibration modes of piezoelectric ceramics has been developed.
[0004]
For example, FIG. 4 shows a basic configuration of a conventional thickness longitudinal vibration piezoelectric transformer, in which FIG. 4 (a) relates to a plan view and FIG. 4 (b) relates to a side sectional view including a displacement stress distribution. .
[0005]
In the case of the piezoelectric transformer using the thickness longitudinal vibration mode, the driving frequency f can be maximized and the electromechanical coupling coefficient k is relatively large, so that the mass m can be reduced and the size can be reduced in order to obtain the same output power P _OUT. Can be configured.
[0006]
However, in the case of a piezoelectric transformer using the thickness longitudinal vibration mode, there are two major problems: structural support difficulty and spurious radiation.
[0007]
That is, referring to the displacement stress distribution diagram of FIG. 4B, when, for example, a secondary resonance occurs in the thickness direction, there are two nodal surfaces M that become zero displacement upon vibration. Normally, input / output signal terminals in piezoelectric transformers use nodal surfaces M and nodes with zero displacement to prevent displacement, but electrode terminals of a finite size (soldered) are used for longitudinal vibrations with small thickness dimensions. It is extremely difficult to attach a lead wire or the like to a vibration node (node M or node). In the thickness longitudinal vibration mode with a high driving frequency f, vibrations of other modes having a lower resonance frequency such as length, width, and sliding vibration, and vibrations of these higher-order modes become infinite spurious radiations, which are main resonances. It will appear in the vicinity and will be a major obstacle when driving.
[0008]
Therefore, in order to solve such problems, a piezoelectric transformer using an energy confinement phenomenon in which vibration energy is distributed to a part of a piezoelectric member in a limited manner and its peripheral portion does not vibrate has been developed.
[0009]
5A and 5B show the basic configuration of a conventional energy confinement type thickness longitudinal vibration piezoelectric transformer. FIG. 5A shows a plan view and FIG. 5B shows a side sectional view.
[0010]
In this energy confining thickness longitudinal vibration type piezoelectric transformer, a rectangular columnar laminated body formed by laminating a predetermined number of square piezoelectric plates is disposed so as to face each other in the thickness direction and form a pair. There are electrodes 22 and 23 for output and output electrodes 24 and 25 provided in pairs, respectively, and they are adjacent to each other in the thickness direction sandwiched between the input electrodes 22 and 23 and the internal electrodes of the output electrodes 24 and 25. The square piezoelectric plate layers are polarized in directions opposite to each other in the thickness direction, and can support a non-vibrating region around the central portion. Since the input electrode 23 and the output electrode 24 are close to each other, they are assumed to be disposed at the same position in FIG.
[0011]
In the case of this piezoelectric transformer, only the main resonance is strongly excited by the energy confinement phenomenon, so that spurious radiation due to vibrations of other modes having low resonance frequencies such as length, width, and sliding vibration can be limited to some extent. It has become.
[0012]
[Problems to be solved by the invention]
In the case of an energy confinement thickness longitudinal vibration type piezoelectric transformer using the above-described square piezoelectric plate, only the main resonance is strongly excited by the energy confinement phenomenon, so that other modes with low resonance frequencies such as length, width, and sliding vibration are used. Spurious radiation due to vibration can be limited to some extent, but it is difficult to accurately suppress spurious radiation due to the combination of vibrations of other modes and vibrations of higher modes in the thickness longitudinal vibration mode with a high driving frequency. There's a problem.
[0013]
The present invention has been made to solve such problems, and its technical problem is to use a small energy confinement vibration mode with excellent basic performance capable of accurately suppressing spurious radiation even at a high driving frequency. The object is to provide a piezoelectric transformer.
[0014]
[Means for Solving the Problems]
According to the present invention, a plurality of counter electrodes opposed to each other in the thickness direction are arranged in a local portion of a laminate formed by laminating a predetermined number of piezoelectric plates, and a part of the plurality of counter electrodes is arranged. In a piezoelectric transformer that is used as an input electrode for obtaining excitation of an energy confinement vibration mode of thickness vibration, and the other portion is used as an output electrode for extracting an output voltage accompanying the energy confinement vibration, a predetermined number of The piezoelectric plate has a disk shape, and the input electrode and the output electrode are formed in a circular shape, and a piezoelectric transformer having a cylindrical structure as a laminated body is obtained.
[0015]
Further, according to the present invention, in the piezoelectric transformer, the disk-shaped piezoelectric plate is a piezoelectric ceramic disk, and the cylindrical laminate is a piezoelectric transformer formed by bonding or bonding piezoelectric ceramic disks, or The disk-shaped piezoelectric plate is a piezoelectric single crystal disk, and the cylindrical laminated body is a piezoelectric transformer formed by bonding or bonding piezoelectric single crystal disks.
[0016]
Furthermore, according to the present invention, in any one of the above-described piezoelectric transformers, the lead electrode for taking out the input electrode and the output electrode to the outside is different from the others having different potentials in the thickness direction of the cylindrical laminate. A piezoelectric transformer is obtained in which the positions are shifted so as not to overlap.
[0017]
In addition, according to the present invention, in any one of the above-described piezoelectric transformers, a piezoelectric transformer in which an insulating layer is provided between the input electrode and the output electrode can be obtained.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The following examples will be given to describe the piezoelectric transformer of the present invention in detail with reference to the drawings.
[0019]
FIG. 1 shows the basic structure of a piezoelectric transformer according to an embodiment of the present invention. FIG. 1A relates to a plan view, and FIG. 1B relates to a side sectional view. This piezoelectric transformer has a plurality of circular shapes facing each other in the thickness direction at a local part (central part) of a cylindrical laminated body formed by bonding or bonding a predetermined number of piezoelectric ceramic disks as disk-shaped piezoelectric plates. The counter electrodes are arranged, a part of these counter electrodes is used as the input electrodes 32 and 33 for obtaining excitation of the energy confinement vibration mode of thickness vibration, and the other part is energy confinement. It is configured to be used as output electrodes 34 and 35 for taking out an output voltage accompanying vibration.
[0020]
Here, the output electrodes 34 and 35 are also provided in pairs, and the input electrode 33 and the output electrode 34 are also close to each other in this case, so that they are at the same position in FIG. It is assumed that it is arranged.
[0021]
That is, the piezoelectric transformer has a disk-shaped predetermined number of piezoelectric ceramic disks compared to the rectangular columnar laminated structure using the conventional square piezoelectric plate shown in FIG. Further, the output electrodes 34 and 35 are formed in a circular shape, which is different in that the laminated body has a cylindrical laminated structure.
[0022]
Here, the cylindrical laminate is a disc having a diameter of 30 mm and a thickness of 2 mm, and is adjacent to the piezoelectric ceramic circle in the thickness direction sandwiched between the internal electrodes of the input electrodes 32 and 33 and the output electrodes 34 and 35. The plate layers are polarized in directions opposite to each other in the thickness direction, and it is possible to support a non-vibrating region around the central portion.
[0023]
In this piezoelectric transformer, when an AC voltage substantially equal to the resonance frequency of the energy confinement vibration in the thickness longitudinal vibration mode of the cylindrical laminated body (piezoelectric ceramic disk) is applied between the input electrodes 32 and 33, these input electrodes 32. , 33 is excited in the thickness longitudinal vibration mode, and an output voltage is generated between the pair of output electrodes 34, 35 by the piezoelectric effect.
[0024]
For comparison, an energy confinement thickness longitudinal vibration piezoelectric transformer having a rectangular columnar laminate structure using the square piezoelectric plate shown in FIG. 5 was prototyped with a side of 30 mm and a thickness of 2 mm, and the piezoelectric ceramic shown in FIG. The energy confinement thickness of the cylindrical laminate structure using a disk and the input impedance in the short state of the output section with the longitudinal vibration piezoelectric transformer were examined. In the cylindrical laminate structure, it exists in the vicinity of the main resonance. It has been found that the spurious radiation is less than that of the rectangular columnar structure. Also, the output power and transmission efficiency of the two prototype piezoelectric transformers are 95% at 15 W for the cylindrical laminate structure and 95 at 12 W for the rectangular column structure under the limitation of the surface temperature of 50 ° C. %.
[0025]
Incidentally, in the above-described piezoelectric transformer having a cylindrical laminate structure, the piezoelectric ceramic disc as a disc-like piezoelectric plate is a piezoelectric single crystal disc, and the cylindrical laminate is laminated by bonding or bonding the piezoelectric single crystal discs. It is good also as a structure which consists of. In this case, almost the same performance can be obtained.
[0026]
FIG. 2 is a perspective view illustrating a basic configuration of a piezoelectric transformer according to another embodiment of the present invention with a main portion seen through.
[0027]
Compared with the one of the previous embodiment, this piezoelectric transformer has the input electrodes 32 and 33 and the output electrodes 34 and 35 with respect to the extraction electrodes 42 and 43 and the extraction electrodes 44 and 45 for extracting them to the outside. Are differently connected to each other so as not to overlap each other with different potentials in the thickness direction of the cylindrical laminate.
[0028]
In general, in a piezoelectric transformer, electrodes having at least three different potentials of input, output, and ground are required. If all of these electrodes are arranged so as to overlap each other, extraction electrodes 42 and 43 and extraction electrodes 44, 44, Since 45 is polarized, undesirable propagation or reflection may occur when confining the elastic wave. Therefore, it is effective to dispose each extraction electrode 42, 43, 44, 45 so as to satisfy the above-described requirement in order to avoid such a problem.
[0029]
FIG. 3 is an enlarged side sectional view showing the basic structure of a piezoelectric transformer according to another embodiment of the present invention.
[0030]
This piezoelectric transformer is different from that of the previous embodiment in that an insulating layer 36 is provided between the input electrodes 32 and 33 between the input electrodes 32 and 33 and the output electrodes 34 and 35. is doing.
[0031]
The insulating layer 36 sandwiched between the internal electrodes of the input electrodes 32 and 33 and the output electrodes 34 and 35 is made of the same material as the piezoelectric ceramic disk, but is made of another material having a lower dielectric constant. The spurious radiation existing in the vicinity of the main resonance may be effectively suppressed.
[0032]
【The invention's effect】
As described above, according to the piezoelectric transformer of the present invention, the rectangular columnar laminate structure using the existing square piezoelectric plate is improved, and the input electrode and the output electrode are circular using the disk-like piezoelectric plate. Since the cylindrical laminated body structure is used, spurious radiation can be sufficiently suppressed. In addition, the extraction electrodes for taking out the input electrode and the output electrode are arranged so as to be shifted from each other so that they do not overlap each other in the thickness direction of the cylindrical laminate. Therefore, it is possible to prevent polarization between the extraction electrodes during polarization, thereby suppressing generation of propagation or reflection when confining the elastic wave. Furthermore, since the insulating layer is provided between the input electrode and the output electrode, spurious radiation existing in the vicinity of the main resonance can be efficiently suppressed. As a result, a piezoelectric transformer using a small energy confinement vibration mode with excellent basic performance capable of accurately suppressing spurious radiation even at a high driving frequency is realized.
[Brief description of the drawings]
1A and 1B show a basic configuration of a piezoelectric transformer according to an embodiment of the present invention, in which FIG. 1A relates to a plan view and FIG. 1B relates to a side sectional view.
FIG. 2 is a perspective view illustrating a basic configuration of a piezoelectric transformer according to another embodiment of the present invention with a main portion seen through.
FIG. 3 is a side cross-sectional view showing an enlarged main part of a basic configuration of a piezoelectric transformer according to another embodiment of the present invention.
4A and 4B show a basic configuration of a conventional thickness-longitudinal vibration piezoelectric transformer, in which FIG. 4A relates to a plan view and FIG. 4B relates to a side sectional view including a displacement stress distribution.
5A and 5B show a basic configuration of a conventional energy confinement type thickness longitudinal vibration piezoelectric transformer, in which FIG. 5A relates to a plan view and FIG. 5B relates to a side cross-sectional view.
[Explanation of symbols]
22, 23, 32, 33 Input electrode 24, 25.34, 35 Output electrode 36 Insulating layer 42, 43, 44, 45 Lead electrode M Nodal surface

Claims (5)

A plurality of counter electrodes facing each other in the thickness direction are arranged in a local area of a laminate formed by laminating a predetermined number of piezoelectric plates, and a part of the plurality of counter electrodes is confined with energy of thickness vibration. In the piezoelectric transformer which is used as an input electrode for obtaining vibration mode excitation and the other part is used as an output electrode for taking out an output voltage accompanying the energy confining vibration, the predetermined number of piezoelectric plates are discs. The piezoelectric transformer is characterized in that the input electrode and the output electrode are formed in a circular shape, and the laminated body has a cylindrical structure. 2. The piezoelectric transformer according to claim 1, wherein the disk-shaped piezoelectric plate is a piezoelectric ceramic disk, and the cylindrical laminated body is formed by bonding or bonding the piezoelectric ceramic disks. Trance. 2. The piezoelectric transformer according to claim 1, wherein the disk-shaped piezoelectric plate is a piezoelectric single crystal disk, and the cylindrical laminated body is formed by bonding or bonding the piezoelectric single crystal disks. Piezoelectric transformer. 4. The piezoelectric transformer according to claim 1, wherein an extraction electrode for taking out the input electrode and the output electrode to the outside is different in potential in the thickness direction of the cylindrical laminate. A piezoelectric transformer characterized in that the position is shifted so as not to overlap with the one. 5. The piezoelectric transformer according to claim 1, wherein an insulating layer is provided between the input electrode and the output electrode. 6.

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