JP2000252542A - Voltage transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage transformer which is small in size and high in efficiency. SOLUTION: A piezoelectric body 2 which is formed of piezoelectric material and provided with electrodes formed on its surface and magnetic bodies 1a and 1b wound with wires 10a and 10b formed of conductive material are joined together through the intermediary of, at least, a coupler 3a into a voltage transformer, where the piezoelectric body 2 and the magnetic bodies 1a and 1b are arranged so as to be in parallel with each other in a longer direction, the wires 10a and 10b wound on the magnetic bodies 1a and 1b serve as an input part, and the electrodes formed on the piezoelectric body 2 serve as an output part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a voltage converter used for a power converter such as an inverter for a liquid crystal backlight or a DC-DC converter.

[0002]

2. Description of the Related Art In recent years, electromagnetic transformers and piezoelectric transformers have been used as high-voltage output transformers such as inverters for liquid crystal backlights of notebook personal computers and the like. Piezoelectric transformers have been adopted as high-voltage output transformers such as inverters for liquid crystal backlights, taking advantage of the advantages of high efficiency, small size, nonflammability, and low noise as compared with electromagnetic transformers.

The basic structure and operation principle of a piezoelectric transformer are as follows:
An example of a Rosen type piezoelectric transformer will be described with reference to FIG. FIG. 7 is a perspective view of a Rosen-type piezoelectric transformer.
A pair of input electrodes 102 are provided on the upper and lower surfaces of the left half of the rectangular piezoelectric ceramic substrate 101, and the input electrodes are polarized in a direction perpendicular to the upper and lower surfaces. The output electrode 103 is provided on the end face of the right half, and the polarization direction of the right half region is polarized in the longitudinal direction. The input electrode is connected to a power supply 104, and the output electrode is connected to a load 105. When a voltage is applied from the power supply, an electric field is applied in the thickness direction in the left half of the figure, and a longitudinal vibration in the longitudinal direction is excited by a piezoelectric transverse effect displaced in a direction perpendicular to the polarization direction, so that the entire piezoelectric transformer vibrates. Further, in the right half, a mechanical strain occurs in the longitudinal direction, and a potential difference occurs in the polarization direction.
From 03, a voltage having the same frequency as the voltage applied between the input electrodes can be obtained. When a drive voltage having a frequency near the resonance frequency of the piezoelectric transformer is applied between the input electrodes, a voltage higher than the input voltage can be obtained. The stress distribution due to resonance at this time is as shown in FIG. 7 (b), and the amplitude distribution of the displacement is as shown in FIG. 7 (c). The central portion in the longitudinal direction of the piezoelectric ceramic substrate is a node of vibration.

However, such a Rosen-type piezoelectric transformer is not yet used in a step-up transformer of an inverter for lighting a cold-cathode tube (CFL) used for a backlight of a liquid crystal display (LCD) panel of a notebook personal computer. It was necessary to apply a sufficiently large input voltage. For this reason, as shown in FIG. 8, a Rosen-type piezoelectric transformer in which an input portion is laminated with a piezoelectric ceramic 106 and an internal electrode 107 has been devised in order to secure a boost ratio.
The basic operation is the same as that of the piezoelectric transformer shown in FIG. By stacking the input sections, it is possible to lower the input impedance and increase the step-up ratio proportional to the square root of the ratio of the input impedance to the output impedance.

[0005]

However, these conventional piezoelectric transformers require a coil component that resonates at an input capacitance and a drive frequency in order to efficiently input energy to the piezoelectric transformer when forming a drive circuit. there were. Further, when the input side is laminated to increase the boost ratio, the input impedance is reduced, and the efficiency is reduced due to the increased resistance loss at the internal electrodes.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a voltage converter which can be further reduced in size and high in efficiency.

[0007]

[Means to solve the problem]
The present invention solves the problem by providing a voltage converter having the following configuration.

That is, according to the present invention, at least one connector is composed of a piezoelectric material made of a piezoelectric material and having an electrode formed on a part thereof, and a magnetic material made of a magnetostrictive material and wound with a conductive material. The piezoelectric body and the magnetic body are arranged so that their respective longitudinal directions are parallel to each other, and a winding applied to the magnetic body is used as an input part, and an electrode formed on the piezoelectric body. Is a voltage converter having an output section.

Further, according to the present invention, a piezoelectric body made of a piezoelectric material and having an electrode formed in a part thereof, and a magnetic body made of a magnetostrictive material and wound with a conductive material are parallel to each other in longitudinal direction. And at least two connectors are interposed between the piezoelectric body and the magnetic body, and a gap is provided.
A voltage converter using an electrode formed on the piezoelectric body as an output unit. The voltage converter further includes a second magnetic body made of a magnetostrictive material and wound with a conductive material, the piezoelectric body being sandwiched between the two magnetic bodies, It is preferred that at least two connectors and voids are interposed between the body and the body.

In this case, it is further preferable that a structure made of a soft magnetic material is provided so as to connect the ends of the two magnetic bodies. In this way, a magnetic closed circuit is formed, so that the voltage conversion efficiency is further improved.

In these voltage converters, the piezoelectric body has a flat plate shape and has a first main surface and a second main surface.
An electrode may be provided on each main surface, and the space between the electrodes may be polarized in a direction perpendicular to the first main surface.

Alternatively, the piezoelectric body has a plate shape, and has a structure in which a plurality of electrode layers and a plurality of piezoelectric layers made of a piezoelectric material are alternately laminated in a thickness direction, and the plurality of electrode layers are formed of two electrodes. Collectively, the electrode layers in the same electrode group may be electrically connected to each other.

Alternatively, the piezoelectric body may be divided into a plurality of regions in the longitudinal direction, and the polarization in each region may be parallel to the longitudinal direction, and the polarization in adjacent regions may be antiparallel to each other. .

Alternatively, the piezoelectric body has a flat plate shape, and a band-shaped electrode extending perpendicularly to the longitudinal direction is provided at a central portion of the first main surface in the longitudinal direction, and is divided in the longitudinal direction by the band-shaped electrode. The polarization directions of the two regions may be parallel to the longitudinal direction and antiparallel to each other.

Alternatively, at least two band-shaped output members extending in a direction perpendicular to a longitudinal direction in the first surface are provided on a first main surface of the second piezoelectric member, wherein the piezoelectric member has a flat plate shape. An electrode may be provided, and a polarization direction of a region sandwiched between the two band-shaped output electrodes may be parallel to the longitudinal direction.

As a method of electrically connecting and supporting these voltage converters to the outside, electrodes for establishing an electrical connection to the outside of the input section and an electrical connection to the outside of the output section are provided. It is preferable that the terminal is formed on the side surface of the piezoelectric body in the longitudinal direction and at a node of the vibration, and the electrical connection and the mechanical connection with the external circuit are made via the conductor.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle of operation of the present invention will be described with reference to an embodiment. FIG. 1 shows an example of the structure of the voltage converter of the present invention. A magnetic body 1a, 1b made of a rod-shaped magnetostrictive material provided with a winding made of a conductive wire and a flat plate-shaped piezoelectric ceramic substrate (hereinafter referred to as a piezoelectric body) are provided with connectors 3a, 3b, 3c at their longitudinal ends. , 3d. The space between the piezoelectric body 2 and the connector and the space between the magnetic body and the connector are fixed, and the whole is integrated. A portion where the connector is not occupied in the facing portion between the piezoelectric body and the magnetic body is a gap.

Next, the principle of operation will be described below. Here, the rod-shaped magnetic bodies 1a and 1b provided with the windings 10a and 10b made of conductive wires will be described as an input unit, and the flat plate-shaped piezoelectric body 2 will be described as an output unit. An alternating current is passed through a winding made of a conductive wire. As a result, an alternating magnetic field parallel to the longitudinal direction is generated inside the magnetostrictive material surrounded by the windings. As a result, longitudinal stress and displacement proportional to the magnetic field are generated due to the magnetostrictive effect, and the material vibrates in the longitudinal direction. When the frequency of the alternating current flowing through the winding is set so that the half-wavelength of the vibration generated in the magnetic material is equal to the length of the magnetic material, the rod-shaped magnetic material has a mechanical resonance with its central portion in the longitudinal direction as a node. A half-wave standing wave of vibration is excited. At this time, winding may be performed so that the phases of the stresses generated in the magnetic bodies 1a and 1b are aligned. The stress distribution and the amplitude distribution of the displacement at that time are shown in FIG. 1 (b) and FIG. 1 (c). Then, the mechanical vibration energy of the input portions 1a and 1b made of the magnetostrictive material is transmitted to an intermediate piezoelectric body 2 via a connector,
The piezoelectric body 2 is caused to undergo mechanical stretching vibration in a half wavelength mode in the longitudinal direction. This mechanical vibration energy is taken out as a higher voltage high-voltage current between the electrode 5 provided at the center in the longitudinal direction of the piezoelectric body and the electrodes 6a and 6b provided at the ends by the piezoelectric longitudinal effect. Can be. The transformation ratio is proportional to the square root of the ratio of the input impedance to the output impedance.

The connector between the magnetic body and the piezoelectric body may be provided at the antinode of the vibration. If a higher-order vibration mode is used, a plurality of abdominal parts are present, so that connectors can be provided at a plurality of locations. The bonding between the piezoelectric body or the magnetic body and the connector may be performed using a highly rigid adhesive such as an epoxy-based material, or the material of the piezoelectric body and the connecting piece may be made of a ceramic material. The electrodes can also be obtained by sintering integrally. In that case, the connector is preferably polarized in a direction perpendicular to the main surface of the piezoelectric body. Further, the connector itself may be formed of a highly rigid adhesive. Alternatively, the coupler may be formed of a soft magnetic material, and a coupler made of a soft magnetic material may be provided so as to connect the ends of the two magnetic materials with the piezoelectric material interposed therebetween, thereby forming a closed magnetic circuit. .

The winding may be appropriately formed by winding an electric wire coated with an insulating material, by applying a foil made of a conductive material to a magnetic material, or by applying a conductive paste.

According to the present invention, a voltage converter having a small size, high efficiency, low cost, and a high step-up ratio can be obtained. It is described in detail below. The first is miniaturization. Since the input stage acts as an inductance by using this structure,
External inductance components required for the drive circuit of the piezoelectric transformer are not required, and the drive circuit can be reduced in size.

Second, high efficiency. By using this structure, the input side, which was necessary to obtain a high voltage step-up ratio with the piezoelectric transformer, does not need to be a laminated structure, and the loss of the input current increased by the laminated structure at the internal electrodes is eliminated. High efficiency can be achieved.

Third, there is a high step-up ratio. In this structure, since the input impedance is determined by the inductance of the winding applied to the magnetostrictive material, a low impedance can be realized relatively easily, so that the boost ratio determined by the square root of the ratio of the input impedance to the output impedance can be easily increased. It becomes possible.

[0024]

[Embodiment 1] This embodiment has the same structure as that described in principle, and its details will be described with reference to FIG. This voltage converter has a piezoelectric material obtained by sintering a PZT-based material that is also used for a piezoelectric transformer on the input side. The piezoelectric body 2 is made of a ceramic rod. Magnetic body 1
a, 1b, and a piezoelectric body 2 provided at a longitudinal end thereof
The respective contact surfaces were bonded with a thermosetting epoxy adhesive via a, 3b, 3c, and 3d to form an integrated structure. A gap is provided between the magnetic body and the piezoelectric body in a portion not occupied by the connector. The size of this voltage converter is 30mm x 10m
mx 5 mm. Windings 10a and 10b made of conductive wires are formed on the magnetic bodies 1a and 1b. In the middle of the piezoelectric body 2 constituting the output section, a strip-shaped electrode 5 extending in the vertical direction in the longitudinal direction is formed on the main surface in the central portion in the longitudinal direction. These electrodes were formed using a Pd-Ag-based conductive paste, and electrode patterns were formed by screen printing. The polarization treatment was performed in oil, and after the polarization treatment, an aging treatment was performed to produce a piezoelectric body. The polarization direction is the longitudinal direction of the piezoelectric body, but two regions are defined in the longitudinal direction at the center in the longitudinal direction, and the polarization of each region is antiparallel to each other. Here, the length of the region polarized in the longitudinal direction of the piezoelectric body is determined by the condition for impedance matching with the load.

[0025]

Embodiment 2 FIG. 2 is a perspective view of a voltage converter according to the present embodiment. This voltage converter has the same structure as that of the first embodiment except for the piezoelectric body. In the middle, the piezoelectric body that constitutes the piezoelectric body 2 is formed with strip-shaped electrodes 8 and 9 that extend perpendicularly to the longitudinal direction on its opposing main surfaces at two locations in the longitudinal direction, and the piezoelectric body that connects the electrodes. Are polarized in the longitudinal direction. The positions at which these electrodes are formed are determined by conditions for impedance matching with the load. By providing the electrode pattern of the output section in this manner, electrical insulation between the input and the output can be achieved, and therefore, a structure resistant to noise such as power supply noise can be obtained.

[0026]

Embodiment 3 FIG. 3 is a perspective view of a voltage converter according to the present embodiment. This voltage converter has the same structure as that of the first embodiment except for the piezoelectric body. The intermediate piezoelectric body is formed by sintering a plurality of piezoelectric sheets with an internal electrode interposed therebetween, and has a laminated structure in the longitudinal direction. Every other one of the plurality of internal electrodes is divided into two different electrode groups 11 and 12 electrically connected to each other. Although the piezoelectric body is polarized in the longitudinal direction, the polarization of the region adjacent to the internal electrode is antiparallel to each other. And it is the same as Example 1 except that the piezoelectric body has a laminated structure in the longitudinal direction. By laminating the electrodes on the output side in this way, insulation between the input and the output can be achieved, and matching can be easily achieved even with a load having a small impedance.

[0027]

Embodiment 4 FIG. 4 is a perspective view of a voltage converter according to this embodiment. This voltage converter has the same structure as that of the first embodiment except for the piezoelectric body. The intermediate piezoelectric body is formed by sintering a plurality of piezoelectric sheets with an internal electrode interposed therebetween, and has a laminated structure in the thickness direction. The plurality of internal electrodes are divided into two different electrode groups 13 and 14, which are electrically connected every other one. The piezoelectric body is polarized in the thickness direction, but the polarization of the region adjacent to the internal electrode is antiparallel to each other. The third embodiment is the same as the first embodiment except that the first piezoelectric body has a laminated structure in the thickness direction. By laminating electrodes on the output side in this way, insulation between input and output is possible,
Further, it becomes easy to perform matching even with a load having a small impedance.

[0028]

Embodiment 5 FIG. 5 shows a perspective view of this embodiment. This is one in which both ends of two magnetic bodies are connected by soft magnetic bodies 25 and 26 having high magnetic permeability such as permalloy between the respective magnetic bodies. Thereby, the magnetic flux leaking from the magnetostrictive material at the input part of the voltage converter can be reduced. With such a closed magnetic circuit structure, the leakage magnetic noise generated from the end of the magnetostrictive material can be greatly reduced, and the electromagnetic conversion efficiency also increases.

Also, as shown in FIG.
By joining to each of the two soft magnetic materials, the high magnetic permeability material provided for the closed magnetic circuit also serves as a connector.

In the first to fifth embodiments described above, the following can be said. Each of these voltage converters can oscillate in a half wavelength mode as shown in FIGS. 1 (b) and 1 (c). Since the electrical connection with the outside of the voltage converter is located at a node of mechanical resonance vibration in the longitudinal direction of the voltage converter, there is little hindrance to mechanical vibration. For electrical connection, solder or conductive resin is desirable.

The voltage converter is supported by an elastic body such as a silicone adhesive at the center in the longitudinal direction. In order to prevent discharge between the input electrode and the input electrode adjacent to the output electrode, a high withstand voltage resin film such as polyimide may be inserted into the gap between the input and output portions, or a silicone adhesive may be applied.

Next, a method of mounting the voltage converter according to the present invention on a printed circuit board will be described. FIG. 6 shows a state in which a voltage converter provided with an electrode extraction portion at the end surface in the width direction of each piezoelectric body and the center portion in the longitudinal direction of each piezoelectric body is mounted on the printed circuit board 25 as in the first embodiment. Since the electrode take-out position of this voltage converter corresponds to the node of the vibration of the piezoelectric body, not only the electrical connection with the printed circuit board but also the mechanical connection, that is, the support can be performed at this position. Both connections can be made simultaneously by interposing solder between the output electrode of the voltage converter and the printed circuit board. In FIG. 6, the winding terminal 1 provided in the voltage converter
The electrode terminals 20, 21, 23, and 24 formed on the printed circuit board and the electrode terminals 5, 16, 18, 19 and the electrode 17 are 15-2.
Soldered in combinations of 0, 16-23, 18-21, 19-24. By adopting the electrical connection and the mechanical connection structure with the printed board in this way, direct mounting on the printed board in a reflow furnace becomes possible, and the manufacturing cost can be extremely reduced.

[0033]

As described above, according to the present invention, there is no need to provide an external inductance unlike a piezoelectric transformer, so that a voltage converter that is small in size, has high efficiency, is low in cost, and has a high step-up ratio can be obtained. Can be

[Brief description of the drawings]

FIG. 1 is a perspective view of a first embodiment of the present invention.

FIG. 2 is a perspective view of a second embodiment of the present invention.

FIG. 3 is a perspective view of a third embodiment of the present invention.

FIG. 4 is a perspective view of a fourth embodiment of the present invention.

FIG. 5 is a perspective view of a fifth embodiment of the present invention.

FIG. 6 is a perspective view showing how a voltage converter is mounted.

FIG. 7 is a diagram showing a conventional Rosen-type piezoelectric transformer.

FIG. 8 is a diagram showing a conventional laminated piezoelectric transformer.

[Explanation of symbols]

 1a, 1b ··· Magnetic body 2 ··· Piezoelectric body 3a, 3b, 3c, 3d ··· Connector 5, 8, 9, 17 ··· Electrode 6a, 6b ··· Electrode 7 ··· Load 10a, 10b ··· Winding 11, 12, 13, 14 ··· Electrode group 15, 16, 18, 19 ··· Winding terminal 20, 21, 23, 24 ··· Electrode terminal 25, 26 ··· Soft magnetic material 27 ··· Printed circuit board

Claims (10)

[Claims] 1. A piezoelectric body made of a piezoelectric material and having a part of an electrode formed thereon, and a magnetic body made of a magnetostrictive material and wound by a conductive material are bonded via at least one connector. The piezoelectric body and the magnetic body are arranged so that their respective longitudinal directions are parallel to each other, and a winding applied to the magnetic body is an input unit, and an electrode formed on the piezoelectric body is an output unit. A voltage converter, characterized in that: 2. A piezoelectric body made of a piezoelectric material and partially formed with electrodes, and a magnetic body made of a magnetostrictive material and wound with a conductive material so that their longitudinal directions are parallel to each other. And at least two connectors are interposed between the piezoelectric body and the magnetic body, and a gap is provided between the piezoelectric body and the magnetic body. The winding unit is used as an input unit, and the electrodes formed on the piezoelectric body are output. A voltage converter characterized in that it is a part. A second magnetic body made of a magnetostrictive material and wound with a conductive material, wherein the piezoelectric body is sandwiched between the two magnetic bodies; 3. The voltage converter according to claim 2, wherein at least two connectors and an air gap are interposed therebetween. 4. A piezoelectric device according to claim 1, wherein said piezoelectric body has a plate-like shape,
4. An electrode is provided on each main surface, and the space between the electrodes is polarized in a direction perpendicular to the first main surface. A voltage converter according to any one of the above. 5. A piezoelectric device according to claim 1, wherein said piezoelectric body has a plate-like shape, and has a structure in which a plurality of electrode layers and a plurality of piezoelectric layers made of a piezoelectric material are alternately laminated in a thickness direction. 4. The electrode layers of the same electrode group being grouped together and being electrically connected to one another.
The voltage converter according to any one of the above. 6. The piezoelectric body is divided into a plurality of regions in the longitudinal direction, wherein the polarization of each region is parallel to the longitudinal direction, and the polarization of adjacent regions is antiparallel to each other. The voltage converter according to any one of claims 1 to 3, wherein 7. The piezoelectric body has a flat plate shape, and a band-shaped electrode extending perpendicularly to the longitudinal direction is provided at a central portion of the first main surface in the longitudinal direction, and is divided in the longitudinal direction by the band-shaped electrode. 4. The voltage converter according to claim 1, wherein the polarization directions of the two regions are parallel to the longitudinal direction and antiparallel to each other. 8. A piezoelectric device according to claim 1, wherein said piezoelectric body has a flat plate shape, and said first main surface of said second piezoelectric body has at least two strip-shaped output members extending in a direction perpendicular to a longitudinal direction in said first surface. 4. The voltage converter according to claim 1, wherein an electrode is provided, and a polarization direction of a region sandwiched between the two band-shaped output electrodes is parallel to the longitudinal direction. 5. 9. An electrode terminal is formed on a side surface in the longitudinal direction of the piezoelectric body and at a vibration node in order to provide an electrical connection with the outside of the input section and support a voltage converter. The voltage converter according to any one of claims 1 to 8, wherein: 10. A soft magnetic material is provided so as to connect ends of the two magnetic bodies.
2. The voltage converter according to 1.