JPH10229228A - Piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric transformer having high mechanical strength and high-energy conversion efficiency. SOLUTION: A piezoelectric transformer is constituted by alternately laminating electrode layers 21, in each of which a plurality of belt-like electrodes, which extend in the width direction W of a rectangular plate 10 from one side face of the plate 10 are arranged in parallel with each other in the length direction L of the plate 10, and electrode layers 22, in each of which a plurality of belt-like electrodes extended in the width direction W of the plate 10 from the other side face are arranged in parallel with each other in the length direction L of the plate 10, so that the electrodes may be positioned between the first belt-like electrodes, upon another in the thickness direction T of the plate 10 and connecting the electrode layers are respectively connected to each other through side-face electrode layers 31, 32, 51, and 52. Since the electrode layers 21 and 22 are laminated upon another in the thickness direction of the rectangular plate 10, and the direction of polarization is substantially oriented to the length direction of the plate 10, the transformer has a high mechanical strength and a high-energy conversion efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer utilizing a longitudinal resonance mode of a rectangular plate made of piezoelectric ceramics, and more particularly to a piezoelectric transformer suitable for use in an AC adapter used in various portable electronic devices. For transformers.

[0002]

2. Description of the Related Art With the spread of various portable electronic devices such as portable televisions and notebook personal computers, as one means for supplying a DC voltage to these portable electronic devices,
AC that outputs DC voltage using commercial AC voltage as input power
There is Ada pig. FIG. 5 is a block diagram showing a circuit configuration of a conventional general AC adapter. Referring to FIG.
This AC adapter is a common mode chopper coil 71
, A full-wave rectifier circuit 72, a smoothing capacitor 73, a switching circuit 74, an electromagnetic transformer 75, and a rectifier circuit 7.
6 and a smoothing circuit 77. Including the above example,
Among the electronic components used in conventional AC adapters,
The electromagnetic transformer has a large volume and affects the conversion efficiency of the AC adapter.

In recent years, there has been an increasing demand for higher efficiency, smaller size, lower electromagnetic noise and lower power consumption for AC adapters, and piezoelectric transformers using mechanical vibration energy as an energy conversion medium in place of the electromagnetic transformer have been developed. Practical use is being studied. For the efficiency of the piezoelectric transformer, impedance matching between the output resistance and the load resistance of the piezoelectric transformer is important, and when the matching is good, mechanical vibration energy can be efficiently converted to electrical energy. A
The input resistance of various portable electronic devices connected to the output section of the C adapter is about several ohms to several tens of ohms, and the output resistance of the piezoelectric transformer needs to be several ohms to several tens of ohms.

[0004] The output resistance R of the piezoelectric transformer is determined by the product of the reciprocal of the resonance angular frequency (ω) and the reciprocal of the braking capacity (Cd2) of the output section, as shown in the following equation 1.

R = (1 / ω) · (1 / Cd2) (1) Here, as a general AC adapter, R is 10 ohms, and ω = 2 · π · fo is approximately 6.28 × 100 KHz.
When the braking capacity of the piezoelectric transformer output section is calculated using the value of Cd2, Cd2 is 160 nF, which is a relatively large value. In order to configure a large capacitance applied to the output portion of the piezoelectric transformer inside an AC adapter having practical dimensions, a laminated structure in which an opposing internal electrode is embedded in the output portion may be considered.

[0006]

In order to adopt a laminated structure having opposing internal electrodes on the output side for impedance matching, the laminating direction of the internal electrodes and the ceramic must be in the length direction of the piezoelectric ceramic rectangular plate. There are two methods: a matching method and a method in which the lamination direction of the internal electrodes and the ceramics matches the thickness direction of the piezoelectric ceramic rectangular plate.

In the former, a so-called piezoelectric longitudinal effect, in which the polarization direction and the vibration direction coincide, is used, and a high electromechanical coupling coefficient is obtained, so that the energy conversion efficiency of the piezoelectric transformer is good. However, when the lamination direction coincides with the length direction of the piezoelectric ceramic rectangular plate, the metal that is the internal electrode layer and the piezoelectric ceramic do not cause a chemical reaction but are only mechanically fixed, so the piezoelectric transformer is When driven near the resonance frequency in the length direction, there is a problem that a tensile stress acts in the length direction and breakage occurs at a boundary surface between the internal electrode and the ceramic. Furthermore, lamination in the length direction requires a large number of laminations, which is a problem in the manufacturing process.

In the latter case, the so-called piezoelectric transverse effect, in which the polarization direction and the vibration direction are orthogonal to each other, is used, and the electromechanical coupling coefficient is only about half of the piezoelectric longitudinal effect. There is a problem that the efficiency is poor. In addition, regarding the laminated structure of the input part of the piezoelectric transformer, the braking capacity is determined by the transformation ratio in the transformer design, and the mechanical strength at the time of excitation and the efficiency of converting input electric energy to the energy of mechanical vibration and the problem of the laminated structure Is the same as the output unit.

An object of the present invention is to provide a piezoelectric transformer having high mechanical strength and high energy conversion efficiency.

[0010]

According to the present invention, in a piezoelectric transformer utilizing a longitudinal resonance mode of a rectangular plate made of a piezoelectric material, a first portion substantially half the length of the rectangular plate is provided. A first electrode layer in which a plurality of first strip-shaped electrodes extending in the width direction of the rectangular plate from one side surface of the rectangular plate are arranged in parallel in the length direction of the rectangular plate, and the other side surface of the rectangular plate A plurality of second electrodes arranged in parallel so that a plurality of second band-shaped electrodes extending in the width direction of the rectangular plate from above are positioned in the longitudinal direction of the rectangular plate and in the middle of the plurality of first band-shaped electrodes arranged in parallel. Layers are alternately stacked in the thickness direction of the rectangular plate,
The first and second electrode layers are connected by first and second side electrode layers formed on one and the other side surfaces of the rectangular plate, respectively, and substantially the other half in the longitudinal direction of the rectangular plate A third electrode layer in which a plurality of third strip-shaped electrodes extending in the width direction of the rectangular plate from one side surface of the rectangular plate are arranged in parallel in the length direction of the rectangular plate; A plurality of fourth band-shaped electrodes extending in the width direction of the rectangular plate from the other side surface of the plate are arranged in parallel in the length direction of the rectangular plate and in the middle of the third band-shaped electrodes arranged in parallel. And a fourth electrode layer are alternately stacked in the thickness direction of the rectangular plate, and the third and fourth electrode layers are
A piezoelectric transformer characterized by being connected by third and fourth side electrode layers formed on one and the other side surfaces of the rectangular plate.

According to the present invention, the first or second electrode layer is formed on at least one of the upper and lower surfaces of the rectangular plate at a first portion substantially half in the longitudinal direction of the rectangular plate. The third or fourth electrode layer is provided on at least one of the upper and lower surfaces of the rectangular plate in a second portion that is approximately half the length of the rectangular plate in the remaining length direction. And the piezoelectric transformer is also laminated.

In a piezoelectric transformer utilizing a length resonance mode of a ceramic rectangular plate, an interdigital electrode structure in which an output side electrode structure is opposed to a longitudinal direction of the rectangular plate is disclosed in Japanese Patent Application No. Hei 6 (1994) -197686.
And Japanese Patent Application No. Hei 6-280590. However, this structure is a structure in which a large boost ratio can be obtained when the load resistance is a very large value of 10 K to 10 MΩ, and a structure utilizing the piezoelectric lateral effect in which the input side is polarized in the thickness direction. Therefore, the structure and the purpose are different from those of the present invention.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A piezoelectric transformer according to an embodiment of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 is a perspective view showing a piezoelectric transformer according to an embodiment of the present invention. FIG.
FIGS. 2A and 2B are cross-sectional views taken along a cutting plane parallel to upper and lower surfaces of a rectangular plate of the piezoelectric transformer shown in FIG. still,
These drawings are conceptual diagrams, and the dimensions, shape, and number of electrodes and the like are different from actual ones.

Referring to FIG. 1 and FIGS. 2A and 2B, the present piezoelectric transformer is a piezoelectric transformer utilizing a resonance mode in a longitudinal direction L of a rectangular plate 10 made of a piezoelectric material.

The present piezoelectric transformer has a first band-shaped electrode extending in the width direction W of the rectangular plate 10 from one side surface of the rectangular plate 10 at a first portion substantially half in the length direction L of the rectangular plate 10. The first electrode layer 21 includes a plurality of first electrodes 21a arranged in parallel in the length direction L of the rectangular plate 10 and a second band-shaped electrode 22a extending in the width direction W of the rectangular plate 10 from the other side surface of the rectangular plate 10. A plurality of second electrode layers 22 arranged in parallel in the length direction L of the rectangular plate 10 and in the middle of the plurality of first band-shaped electrodes 21 a arranged in parallel are arranged in the thickness direction T of the rectangular plate 10. Are alternately stacked. The first electrode layer 21 is connected by a first side electrode layer 31 formed on one side of the rectangular plate 10. The second electrode layer 22 is connected by a second side electrode layer 32 formed on the other side of the rectangular plate 10. Further, the present piezoelectric transformer has a third band-shaped electrode 41a extending in the width direction W of the rectangular plate 10 from one side surface of the rectangular plate 10 in a second portion which is substantially half the length direction L of the rectangular plate. A plurality of third electrode layers 41 arranged in parallel in the longitudinal direction L of the rectangular plate 10, and a fourth band-shaped electrode 42 a extending in the width direction W of the rectangular plate 10 from the other side surface of the rectangular plate 10. A plurality of fourth electrode layers 42 arranged in parallel in the length direction L of the plate 10 and in the middle of the third band-shaped electrodes 41 a arranged in parallel with each other are arranged in the thickness direction T of the rectangular plate 10. They are alternately stacked. Third electrode layer 21
Are connected by a third side electrode layer 51 formed on one side of the rectangular plate 10. Fourth electrode layer 42
Are connected by a fourth side electrode layer 52 formed on the other side of the rectangular plate 10.

The electrode layer in the piezoelectric transformer according to the present invention has parameters such as the width of the strip electrodes, the parallel pitch, the stacking interval, and the number of strip electrodes. The capacitance of the input / output unit of the piezoelectric transformer depends on these parameters and the number of stacked electrode layers. FIG. 3 is a conceptual diagram for explaining the operation of the piezoelectric transformer according to the present invention, and is a longitudinal sectional view taken along a cut plane parallel to the side surface of the rectangular plate. Although the strip-shaped electrode has a cross-sectional area determined by its width and thickness, it is conceptually regarded as a point here. During polarization or driving, an electric field is applied between the electrode points 121a and 122a. The magnitude V _C of the effective applied voltage parallel to the length direction L of the rectangular plate 110 made of a piezoelectric material is the magnitude of the direction cosine component of the magnitude V of the actual applied voltage between the electrodes. Naturally, the lines of electric force are distributed between the electrode points 121a and 122a with a spread corresponding to one layer thickness, so that the rectangular plate 110 can be polarized or excited in the length direction L thereof. Further, when considering the cross section of the same piezoelectric transformer in the length direction L of the rectangular plate 110, there is a piezoelectric ceramic portion continuous in the length direction L, and therefore, when there is an electrode layer extending orthogonally to the length direction L The tensile strength in the length direction L is greater than that in the length direction L.
When driven in the vicinity of the resonance frequency, the breakage due to the tensile stress in the length direction L is prevented.

[Second Embodiment] A piezoelectric transformer according to a second embodiment of the present invention is a modification of the first embodiment. FIG. 4 is a perspective view showing a piezoelectric transformer according to Embodiment 2 of the present invention.

Referring to FIG. 4, the present piezoelectric transformer is a piezoelectric transformer utilizing a resonance mode in the longitudinal direction L of a rectangular plate 10 made of a piezoelectric material, as in the first embodiment.
In a first portion which is substantially half of the length direction L of the rectangular plate 10,
A first strip-shaped electrode 21a extending in the width direction W of the rectangular plate 10 from one side surface of the rectangular plate 10 is disposed in the longitudinal direction L of the rectangular plate 10.
A plurality of first electrode layers 21 and a rectangular plate 10
Extending in the width direction W of the rectangular plate 10 from the other side surface of
And a second electrode layer 22 in which a plurality of strip electrodes 22a are arranged in the longitudinal direction L of the rectangular plate 10 and in the middle of the plurality of first strip electrodes 21a arranged in parallel.
0 are alternately stacked in the thickness direction T. The first electrode layer 21 is connected by a first side electrode layer 31 formed on one side of the rectangular plate 10. The second electrode layer 22 is connected by a second side electrode layer 32 formed on the other side of the rectangular plate 10. Further, the present piezoelectric transformer includes a rectangular plate 1 on one side surface of the rectangular plate 10 in a second portion that is substantially the other half in the length direction L of the rectangular plate.
0 in the width direction W of the rectangular plate 1
A plurality of third electrode layers 41 arranged in parallel in the length direction L
And a fourth strip-shaped electrode 42a extending in the width direction W of the rectangular plate 10 from the other side surface of the rectangular plate 10 in the longitudinal direction L of the rectangular plate 10 and in the middle of a plurality of parallel third strip-shaped electrodes 41a. Fourth electrode layer 42 arranged in parallel so as to be located
Are alternately stacked in the thickness direction T of the rectangular plate 10. The third electrode layer 21 is connected by a third side electrode layer 51 formed on one side surface of the rectangular plate 10. The fourth electrode layer 42 is connected by a fourth side electrode layer 52 formed on the other side of the rectangular plate 10.

In the piezoelectric transformer according to the second embodiment, a second electrode layer is also laminated on the upper surface of the rectangular plate 10 at a first portion substantially half in the longitudinal direction L of the rectangular plate 10. ing. That is, on the upper surface of the rectangular plate 10, the rectangular plate 10
Extending in the width direction W of the rectangular plate 10 from the other side surface of
A plurality of second electrode layers 22 ′ are stacked in such a manner that the plurality of strip electrodes 22 a ′ are positioned in the longitudinal direction L of the rectangular plate 10 and in the middle of the plurality of parallel first strip electrodes. . Further, in a second portion, which is almost half in the length direction L of the rectangular plate 10, a fourth electrode layer is also stacked on the upper surface of the rectangular plate 10. That is, on the upper surface of the rectangular plate 10,
A fourth band-shaped electrode 42a 'extending in the width direction W of the rectangular plate 10 from the other side surface of the rectangular plate 10 is located in the length direction L of the rectangular plate 10 and in the middle of a plurality of parallel first band-shaped electrodes. The plurality of second electrode layers 42 'arranged in parallel as described above are stacked.

In the present invention, as long as the first and second electrode layers are alternately laminated in the first portion substantially half in the longitudinal direction of the rectangular plate, the first electrode layer is formed. May be laminated on the upper and lower surfaces of the rectangular plate, the second electrode layer may be laminated on the upper and lower surfaces of the rectangular plate, or the first electrode layer may be laminated on one of the upper and lower surfaces of the rectangular plate. In addition, the second electrode layer may be laminated on the other of the upper and lower surfaces of the rectangular plate. In addition, as long as the third and fourth electrode layers are alternately laminated in the second portion of the remaining half of the rectangular plate in the longitudinal direction, the third electrode layer is formed on the upper and lower surfaces of the rectangular plate. Laminated or
Alternatively, the fourth electrode layer may be laminated on the upper and lower surfaces of the rectangular plate, or the third electrode layer may be laminated on one of the upper and lower surfaces of the rectangular plate, and the fourth electrode layer may be laminated on the rectangular plate. It may be laminated on the other of the upper and lower surfaces.

[0022]

Next, an embodiment of the piezoelectric transformer according to the present invention will be described.

Example 1 Example 1 is a specific example of the piezoelectric transformer according to Embodiment 1 shown in FIGS. 1 and 2A and 2B. Hereinafter, the manufacturing process will be described.

A first green sheet made of PZT piezoelectric ceramics and having a length of 32 mm, a width of 10 mm, and a thickness of 120 μm is prepared. For the first green sheet, a first half of the length in the length direction to be an input portion of the piezoelectric transformer
In the part, silver-palladium alloy is used and the width is 100μ.
m, 8 band-shaped electrodes having a length of 9 mm are formed at a pitch of 2 mm, and the second half of the other half in the length direction to be the output portion of the piezoelectric transformer is formed of a silver-palladium alloy and has a width of 100 μm. A 9 mm long strip electrode with a pitch of 50
30 lines are formed at 0 μm.

Similarly, a second PZT piezoelectric ceramic having a length of 32 mm, a width of 10 mm, and a thickness of 120 μm is used.
Prepare a green sheet. In the second green sheet, a first portion, which is a half of the length in the length direction to be an input portion of the piezoelectric transformer, has a width 1
First, a band-shaped electrode having a length of 9 μm and a pitch of 2 mm
The green sheet is formed so as to be shifted from the green sheet by about 1 mm, and the second half of the other half in the length direction, which becomes the output part of the piezoelectric transformer, is also made of silver-palladium alloy and is 100 μm wide and 100 μm long. 9 mm strip electrodes with a pitch of 5
00 μm and about 250 μm from the first green sheet
30 lines are formed with a shift of m.

The first and second green sheets are alternately laminated, and a third green sheet made of PZT-based piezoelectric ceramics having a length of 32 mm, a width of 10 mm and no electrodes is laminated outside the laminate. Fifty layers are laminated to form a rectangular shape, which is sintered at 1100 ° C. in the air, and first to fourth side electrodes are formed on the side surfaces thereof using a silver-palladium alloy.

Further, a polarization process is performed to make the length 27 m.
m, a width of 8.5 mm, and a thickness of 5 mm were manufactured.

Various characteristics such as the optimum load resistance value calculated from the resonance frequency, the input / output braking capacity, and the output braking capacity of the piezoelectric transformer according to Example 1 are shown in Table 1 below.
Shown in Table 1 shows the characteristics measured by using the one-wavelength resonance mode of this piezoelectric transformer, supporting an almost quarter position from the longitudinal end face of the rectangular plate, assuming an input voltage of 100 Vrms and a load resistance of about 30Ω. Also shown.

As a comparative example, a conventional piezoelectric transformer proposed in Japanese Patent Application No. 6-280590 was manufactured with the same dimensions and input / output braking capacity as in the first embodiment. Also in this comparative example, the same items as in Example 1 were measured.
Table 1 shows the results.

[0030]

[Table 1]

As is clear from Table 1, the piezoelectric transformer according to the first embodiment of the present invention has a step-down ratio of four times, and can reduce the input voltage of 100 Vrms to about 5 to 6 V. And the impedance matching is good. The efficiency, which is the power ratio of input and output as a piezoelectric transformer, is as high as 95% or more. In addition, the results of the three-point bending test of the mechanical strength evaluation were almost equal to the strength of the piezoelectric ceramic alone, and the problem of practical strength was solved. On the other hand, in the structure of the piezoelectric transformer of the comparative example, since the piezoelectric side effect is used on the input side, the electromechanical coupling coefficient is small,
Since the conversion efficiency from electrical energy to mechanical vibration energy is low, heat generation is large. As a result, the efficiency is smaller than that of the first embodiment.

Example 2 Example 2 is a specific example of the piezoelectric transformer according to the embodiment 2 shown in FIG.

The same first and second green sheets as in Example 1 were manufactured, and a total of 50 layers of the first and second green sheets were alternately laminated to form a rectangular shape.
After sintering at 100 ° C., first to fourth side electrodes are formed on the side surfaces using a silver-palladium alloy. Furthermore, it is subjected to a polarization treatment, and is 27 mm long, 8.5 mm wide, and 5 mm thick.
The piezoelectric transformer according to Example 2 was manufactured.

With respect to the manufactured piezoelectric transformer according to the second embodiment, the same items as in the first embodiment were measured, and the results are shown in Table 1 above.

The piezoelectric transformer according to the second embodiment has electrodes on the surface, so that the surface and the layers near the surface are piezoelectrically active. Therefore, compared with the first embodiment in which the surface of the piezoelectric transformer has no electrode on the surface and the surface and the layer in the vicinity thereof are piezoelectrically inactive, the heat generation and the efficiency are small, but better results are obtained.

[0036]

According to the piezoelectric transformer of the present invention, a first portion extending in the width direction of the rectangular plate from one side surface of the rectangular plate at a first portion substantially half the length of the rectangular plate made of a piezoelectric material.
A first electrode layer in which a plurality of strip electrodes are arranged in parallel in the length direction, and a second strip electrode extending in the width direction from the other side surface of the rectangular plate are provided between the first strip electrode in the length direction and the first strip electrode. And a plurality of second electrode layers arranged in parallel to each other are alternately stacked in the thickness direction of the rectangular plate. A third electrode layer in which a plurality of third band-shaped electrodes extending in the width direction from one side of the rectangular plate are arranged in parallel in the length direction; and a fourth band-shaped electrode extending in the width direction from the other side of the rectangular plate. Are alternately stacked in the thickness direction so that a plurality of fourth electrode layers are arranged in the length direction and in the middle of the third strip-shaped electrode, and the first to fourth electrode layers are respectively Since the connection is made by the first to fourth side electrode layers formed on the side surfaces of the rectangular plate, the lamination direction of the electrode layers is Is the thickness direction, the substantial polarization direction is the length direction of the rectangular plate, the mechanical strength is high and a high energy conversion efficiency.

[Brief description of the drawings]

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

FIGS. 2A and 2B are cross-sectional views showing the internal structure of the piezoelectric transformer shown in FIG.

FIG. 3 is a conceptual diagram for explaining the operation of the piezoelectric transformer according to the present invention.

FIG. 4 is a perspective view showing a piezoelectric transformer according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing a circuit configuration of a conventional AC adapter using an electromagnetic transformer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Rectangular plate 21 1st electrode layer 21a 1st strip electrode 22, 22 '2nd electrode layer 22a, 22a' 2nd strip electrode 31 1st side electrode layer 32 2nd side electrode layer 41 3rd Electrode layer 41a Third strip electrode 42, 42 'Fourth electrode layer 42a, 42a' Fourth strip electrode 51 Third side electrode layer 52 Fourth side electrode layer 71 Common mode chiyoke coil 72 Full wave Rectifier circuit 73 Smoothing capacitor 74 Switching circuit 75 Electromagnetic transformer 76 Rectifier circuit 77 Smoothing circuit 110 Rectangular plates 121a, 122a Electrode points

Claims (2)

[Claims] 1. A piezoelectric transformer using a resonance mode in a longitudinal direction of a rectangular plate made of a piezoelectric material, wherein a first portion substantially half in the longitudinal direction of the rectangular plate is provided on one side surface of the rectangular plate. And a first electrode layer in which a plurality of first strip-shaped electrodes extending in the width direction of the rectangular plate are arranged in parallel in the length direction of the rectangular plate, and a first electrode layer extending in the width direction of the rectangular plate from the other side surface of the rectangular plate. A second electrode layer in which a plurality of two strip-shaped electrodes are arranged in parallel in the length direction of the rectangular plate and in the middle of the first strip-shaped electrodes arranged in parallel with each other; And the first and second electrode layers are connected by first and second side electrode layers formed on one and other side surfaces of a rectangular plate, respectively. One side of the rectangular plate at a second portion approximately half of the length of the plate Third the third strip electrodes extending in the width direction of the rectangular plate formed by a plurality of parallel in the longitudinal direction of the rectangular plate from
And a fourth band-shaped electrode extending in the width direction of the rectangular plate from the other side surface of the rectangular plate is positioned in the length direction of the rectangular plate and in the middle of the third band-shaped electrodes arranged in parallel. And a plurality of fourth electrode layers arranged in parallel with each other are alternately stacked in the thickness direction of the rectangular plate.
Wherein the electrode layers are connected by third and fourth side electrode layers formed on one and the other side surfaces of the rectangular plate, respectively. 2. The method according to claim 1, wherein the first or second electrode layer is laminated on at least one of upper and lower surfaces of the rectangular plate at a first portion substantially half in a longitudinal direction of the rectangular plate. The second portion, which is approximately half the length of the rectangular plate in the length direction,
The piezoelectric transformer according to claim 1, wherein the fourth electrode layer is also laminated on at least one of upper and lower surfaces of the rectangular plate.