JPH11298056A - Piezoelectric transformer and driving method thereof - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To take out a plurality of output terminals with one piezoelectric transformer. SOLUTION: This piezoelectric transformer includes a low impedance layer 112 composed of a plurality of piezoelectric layers and polarized in the thickness direction and a high impedance layer 111 composed of a single layer or a plurality of piezoelectric layers and also polarized in the thickness direction. Assume that they are integrally connected along the longitudinal direction. Further, the external output terminal 11 is taken out from at least one of the internal electrodes of the low impedance layer. Further, when the total length of the piezoelectric transformer is L, the external connection terminals are arranged at L / 4 positions from both ends. The piezoelectric transformer having the above structure is driven at the resonance frequency of the longitudinal longitudinal vibration secondary mode in which one wavelength is equal to the total length L of the piezoelectric transformer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer used in various power supply circuits for generating a high voltage and a driving method thereof, and more particularly to a piezoelectric transformer for a power supply circuit which is small and requires a high step-up ratio.

[0002]

2. Description of the Related Art FIG. 15 shows the structure of a Rosen type piezoelectric transformer which is one of the conventional piezoelectric transformers. This piezoelectric transformer has advantages such as miniaturization, non-combustibility, and no generation of noise due to electromagnetic induction as compared with the electromagnetic transformer. A portion indicated by 211 is a low impedance portion of the piezoelectric transformer, and serves as an input portion when used for boosting. The low impedance portion 211 is polarized in the thickness direction, and the electrodes 113U and 113D are provided on the main surface in the thickness direction.
Is arranged. On the other hand, a portion indicated by 212 is a high impedance portion, and becomes an output portion when used for boosting. The high impedance portion 212 is polarized in the longitudinal direction, and the electrode 114 is disposed on the end face in the longitudinal direction. The operation of this piezoelectric transformer is based on the input electrode 113.
When a voltage is applied to U and 113D, electric energy is converted into mechanical energy by the (reverse) piezoelectric effect, and longitudinal vibration in the longitudinal direction is excited. The energy ratio at this time is the electromechanical coupling coefficient k31. When the driving frequency is near the resonance frequency of the primary mode or the secondary mode of the longitudinal longitudinal vibration, large mechanical vibration also occurs in the output unit 212. In the output unit 212, mechanical energy is converted into electric energy by the piezoelectric effect, and a voltage is generated. The energy ratio at this time is the electromechanical coupling coefficient k33. At this time, in the output section 212, the polarization direction is the length direction, and the length is larger than the thickness, so that a high voltage can be easily obtained from the electrode 114.

[0003]

In a conventional Rosen-type piezoelectric transformer, one set of input terminal and one set of output terminal are provided. Therefore, when multiple output terminals are required,
As many piezoelectric transformers as required output terminals are required. In a conventional Rosen-type piezoelectric transformer, an electrode is provided on an end face in the longitudinal direction, and the position of the electrode becomes a vibration antinode in the longitudinal vibration. For this reason, if a conductor is connected to the end face, vibration is hindered, and as a result, high output cannot be transmitted with high efficiency. Furthermore, there is a disadvantage that the lead wire connected at the time of large amplitude is cut, and there is a problem in reliability.

Accordingly, an object of the present invention is to realize a piezoelectric transformer having a plurality of output terminals,
An object of the present invention is to provide a highly reliable piezoelectric transformer.

[0005]

In order to achieve the above object, the present invention comprises a piezoelectric layer composed of a plurality of layers each of which is polarized in a thickness direction, and an internal electrode interposed between the piezoelectric layers composed of the plurality of layers. The low-impedance portion, the same thickness as the low-impedance portion, a high-impedance portion composed of a single-layer piezoelectric layer polarized in the thickness direction is integrally formed along the longitudinal direction, and both surfaces of the low-impedance portion and the In a piezoelectric transformer having external electrodes provided on both surfaces of a high impedance portion, at least one of the external electrode and the internal electrode of the low impedance portion is connected to an external connection terminal.

Further, a low-impedance portion composed of a plurality of piezoelectric layers each of which is polarized in the thickness direction, an internal electrode interposed between the plurality of piezoelectric layers, and each layer having the same thickness as the low-impedance portion. A plurality of piezoelectric layers polarized in the thickness direction, and a high impedance portion composed of internal electrodes interposed between the plurality of piezoelectric layers are integrally formed along the longitudinal direction, and both surfaces of the low impedance portion are formed. And a piezoelectric transformer having external electrodes provided on both surfaces of the high impedance portion, wherein the external electrode and at least one of the internal electrodes of the low impedance portion or the high impedance portion are connected to an external connection terminal.

The length of the piezoelectric transformer in the longitudinal direction is represented by L
In this case, the external connection terminal of the low impedance portion or the high impedance portion is arranged at a position of L / 4 from one side end or the other side end.

Further, the method for driving the piezoelectric transformer is characterized in that the piezoelectric transformer is driven at a resonance frequency in a longitudinal longitudinal vibration secondary mode in which one wavelength is equal to the total length L of the piezoelectric transformer.

[0009]

Embodiments of the present invention will be described below.

(Embodiment 1) FIG. 1 shows the structure of a piezoelectric transformer according to a first embodiment of the piezoelectric transformer according to the present invention. 112 is a low impedance part, 15 is a piezoelectric layer of the low impedance part, 16
Is an internal electrode.

As shown in FIG. 1, the low impedance portion is constituted by alternately laminating two piezoelectric layers and one internal electrode.

Reference numeral 111 denotes a high impedance section,
Indicates a piezoelectric layer of a high impedance portion. The piezoelectric layer is composed of one piezoelectric layer having the same thickness as the low impedance portion.

As shown in FIG. 1, this piezoelectric transformer has external electrodes 12U,
Electrical connection is made from the 2D, the internal electrode 16, and the external electrodes 13U, 13D provided on the upper and lower main surfaces of the high impedance portion. When the external electrodes provided on the upper and lower main surfaces of the high impedance portion are the total length L of the piezoelectric transformer, L /
2 or less. In addition, the upper and lower main surfaces of the low impedance portion and the internal electrode are also formed at a maximum of L / 2 or less from the end surface.

The operation of the piezoelectric transformer configured as described above will be described below. The lumped constant approximation equivalent circuit near the resonance frequency of the present piezoelectric transformer is as shown in FIG.

In FIG. 2, Cd1, Cd2-1, Cd2-2
Is the constrained capacitance on the input side and output side respectively, A1 (input side), A21 and A22 (output side) are force coefficients, m is equivalent mass, C is equivalent compliance, and Rm is equivalent mechanical resistance. In the piezoelectric transformer of this embodiment, since each layer of the output section is thinner than the thickness of the input section, the force coefficient A1 is A
21, A22, and are boosted by two equivalent ideal transformers in FIG. Further, since the piezoelectric transformer includes a series resonance circuit having an equivalent mass and an equivalent compliance, the output voltage has a value larger than the transformation ratio of the transformer, particularly when the value of the load resistance is large.

In the present embodiment, A21 and A22 can be set to the same value by making the thicknesses of the piezoelectric layers 15 in the low-impedance portion equal.

The piezoelectric transformer can be made of a PZT (PbZrO3 -PbTiO3) piezoelectric material by bonding and laminating the piezoelectric transformer. First, a plate having a thickness of a piezoelectric layer is sintered, and external electrodes and internal electrodes are formed at desired positions by depositing Au on the surface of the piezoelectric sintered body.

After the electrodes are formed, polarization is performed. Thereafter, lamination is performed by adhesion. After bonding, the end face is polished to expose the internal electrode to the end face, and is connected to the internal electrode with a conductive resin. Here, the lamination was performed by bonding, but using a piezoelectric material having piezoelectricity and an electrode material that can be integrally fired therewith, the piezoelectric material and the electrode material were stacked before sintering the piezoelectric body, and simultaneously fired. Thus, the transformer structure shown in FIG. 1 can be formed.

The thickness of each piezoelectric layer was 0.5 mm, and the total thickness was 1.0 mm. Also, the overall length is 40mm and the width is 7m
m.

The resonance frequency of the secondary longitudinal mode of the piezoelectric transformer is 86 kHz from the admittance frequency characteristic.
Measured as z. When a load resistance of 100 kΩ was connected to each output section of this piezoelectric transformer, an output of 350 V was obtained for an input voltage of 10 V, and the output power at this time was 1.3 W, and a plurality of output powers were obtained. Was taken out.

In the present invention, when the length of the electrical connection is L in the longitudinal direction of the piezoelectric transformer, the external connection terminal of the low impedance portion or the high impedance portion is connected to one end surface or the other end surface of the piezoelectric transformer in the longitudinal direction. To L / 4 from FIG. 3 shows the distribution of the displacement and stress of the rod-shaped vibrator 31. FIG. 3 shows the distribution of the longitudinal longitudinal vibration secondary mode,
This is a vibration mode in which one wavelength is equal to the length of the vibrator 31.
In this case, as is clear from FIG. 3, there is a vibration node inside the vibrator 31 by one quarter from both ends. Therefore, if the terminal is connected to the position of L / 4 from both ends in the longitudinal direction of the piezoelectric transformer and driven at the resonance frequency of the longitudinal longitudinal vibration secondary mode, the external connection terminal does not adversely affect the vibration. In addition, it is possible to cope with the problem that the lead wire is cut at the time of large amplitude.

Furthermore, in the piezoelectric transformer of this configuration, when only one output is required, the output can be controlled and the piezoelectric transformer can be driven by connecting a control load to one output. No.

FIG. 4 shows a case where the input section has a laminated structure. FIG. 5 shows a sectional structural view of the input unit. In this way, the piezoelectric transformers are formed of odd-numbered piezoelectric active layers, internal electrodes and external electrodes 33U, 33D, 33U provided on the upper and lower main surfaces.
With the configuration of a and 33Da, the layer thickness per layer of the input section is smaller than the respective layer thicknesses of the output section, and A1 can be smaller than A21 and A22.

(Embodiment 2) FIG. 6 is a view showing the structure of a piezoelectric transformer according to a second embodiment of the piezoelectric transformer according to the present invention. 112 is a low impedance part, 15 is a piezoelectric layer of the low impedance part, 16
Is an internal electrode. 111 is a high impedance part, and 14 is a piezoelectric layer of the high impedance part. The above is the same as the configuration in FIG. The difference from the configuration of FIG. 1 is that the size of the external electrodes 22U and 22D of the low impedance portion on the upper and lower main surfaces is changed.

The operation of the piezoelectric transformer configured as described above will be described below. By changing the electrode size of the upper and lower main surfaces of the output unit, the values of A21 and A22 and the output capacitances Cd2-1 and Cd2-2 can be changed in the upper and lower layers in the lumped constant approximation equivalent circuit of FIG. As described above, it is possible to obtain a piezoelectric transformer in which the external electrodes in the low-impedance portion are adapted to a load even when the upper and lower main surfaces have different loads.

In the piezoelectric transformer of the present embodiment, as in the first embodiment, since each layer of the output section is thinner than the thickness of the input section, the force coefficient A1 is larger than A21 and A22. Boosted by two equivalent ideal transformers.

A piezoelectric transformer having a different impedance ratio between the two outputs as shown in Embodiment 2 was laminated and formed by bonding. The method of lamination by adhesion and the method of polarization are the same as in the first embodiment. Here, the overall dimensions were 40 mm, the width was 7 mm, and the thickness was 1.2 mm.

The resonance frequency of the secondary mode in the longitudinal longitudinal vibration mode of this piezoelectric transformer is 83% from the admittance frequency characteristic.
kHz. When a load resistance of 100 kΩ, which is relatively low resistance for high voltage use, is connected to this piezoelectric transformer, 100 V, 50 V is applied to the input voltage of 10 V.
Is obtained, the output power at this time is 1.3W,
It was 0.9W.

Further, in the case of the piezoelectric transformer of this configuration, when only one output is required, it is needless to say that the output can be controlled and the piezoelectric transformer can be driven by connecting a control load to one output. No.

As in the first embodiment, when the length of the piezoelectric transformer is L, a terminal is connected to a position of L / 4 from the end face, and the piezoelectric transformer is driven at the resonance frequency of the longitudinal longitudinal vibration secondary mode. Also, it is possible to cope with the problem that the lead wire is cut off at the time of large amplitude without adversely affecting the vibration at the terminal.

The structure of the input section is the same as that shown in FIG. 5, and the piezoelectric transformer also has a laminated structure as shown in FIG. A1 can be made thinner than A1, A2, A2
It can be smaller than 2.

(Embodiment 3) As a third embodiment of the piezoelectric transformer according to the present invention, FIG. 8 shows a perspective view of a structural example of the piezoelectric transformer. 112 is a low impedance part, 15 is a piezoelectric layer of the low impedance part, 16
Is an internal electrode. 111 is a high impedance part, and 14 is a piezoelectric layer of the high impedance part. The low impedance portion has a structure in which eight piezoelectric layers and seven internal electrodes are alternately stacked. The high impedance portion has the same thickness as the low impedance portion, and has a single piezoelectric layer structure. FIG. 9 is a cross-sectional view of the low impedance section (AA ′ in FIG. 8) according to the third embodiment. The difference from the configuration of FIG. 1 is that the low impedance section has a laminated structure.

The operation of the piezoelectric transformer configured as described above will be described below. The output impedance can be reduced by increasing the number of stacked output units. Further, in the lumped constant approximation equivalent circuit of FIG. 2, the values of A21 and A22, the output capacitances Cd2-1 and Cd2-2.
Can be changed. This makes it possible to obtain a piezoelectric transformer suitable for different loads, even for different loads.

A piezoelectric transformer in which the impedance ratio of two outputs is changed as shown in Embodiment 3 was manufactured by adhesive lamination. Embodiment 1 is a method of adhesion lamination and polarization.
Is the same as Here, the overall dimensions are 40mm, width 7m
m and a thickness of 1.8 mm.

The resonance frequency of the secondary mode in the longitudinal longitudinal vibration mode of this piezoelectric transformer is 83% from the admittance frequency characteristic.
kHz. When a load resistance of 10 kΩ, which is relatively low resistance for high voltage use, is connected to this piezoelectric transformer, output voltages of 120 V and 60 V are obtained with respect to an input voltage of 10 V, and the output power at this time is 1.0 W, 0 V. .
It was 5W.

Further, even when only one output is required in the piezoelectric transformer of this configuration, it is needless to say that the output can be controlled and the piezoelectric transformer can be driven by connecting a control load to one output. No.

(Embodiment 4) As a fourth embodiment of the piezoelectric transformer according to the present invention, FIG. 10 shows a perspective view of a structural example of the piezoelectric transformer. 112 is a low impedance part, 15 is a piezoelectric layer of the low impedance part, and 1
6 is an internal electrode. Reference numeral 111 denotes a high impedance portion, and reference numeral 14 denotes a piezoelectric layer of the high impedance portion.
The low impedance portion is configured by alternately stacking four piezoelectric layers and three internal electrodes. The high impedance section is composed of a single piezoelectric layer having the same thickness as the low impedance section.
FIG. 11 is a cross-sectional view of a low impedance part according to the fourth embodiment.

As shown in FIG. 11, this piezoelectric transformer has external electrodes 12U provided on upper and lower main surfaces of a low impedance portion.
Electrical connection is made from the internal electrodes 12D, the internal electrodes 16, and the external electrodes 13U and 13D provided on the upper and lower main surfaces of the high impedance portion. The external electrodes provided on the upper and lower main surfaces of the high-impedance portion have a total length L of the piezoelectric transformer.
/ 2 or less. In addition, the upper and lower main surfaces of the low impedance portion and the internal electrode are also formed at a maximum of L / 2 or less from the end surface. The difference from the configuration of FIG.
This is the point that three output terminals are taken out.

The operation of the piezoelectric transformer configured as described above will be described below. A lumped constant approximation equivalent circuit near the resonance frequency of the present piezoelectric transformer is as shown in FIG.

In FIG. 12, Cd1a, Cd2-1a, C
d2-2a and Cd2-3a are the capacities on the input side and the output side, respectively, A1a (input side), A21a, A22a and A
23a (output side) is a force coefficient, ma is an equivalent mass, Ca is an equivalent compliance, and Rma is an equivalent mechanical resistance. In the piezoelectric transformer according to the present embodiment, since each layer of the output section is thinner than the thickness of the input section, the force coefficient A1a is A21a.
, A22a, and A23a, and are boosted by three equivalent ideal transformers in FIG. Further, since the piezoelectric transformer includes a series resonance circuit having an equivalent mass and an equivalent compliance, the output voltage has a value larger than the transformation ratio of the transformer, particularly when the value of the load resistance is large.

As described above, it is needless to say that a plurality of output terminals can be provided by obtaining a necessary number of electrical connections from the internal electrodes.

In the piezoelectric transformer of this embodiment, A21a, A21a,
A22a, A23a value, output capacitance Cd2-1a, Cd2
-2a and Cd2-3a can be changed. This makes it possible to obtain a piezoelectric transformer suitable for different loads even when the load is different.

(Embodiment 5) As a fifth embodiment of the piezoelectric transformer according to the present invention, FIG. 13 is a view showing the structure of a piezoelectric transformer. 112 is a low impedance part, 45 is a piezoelectric layer of the low impedance part, and 16
Is an internal electrode. 111 is a high impedance part, and 14 is a piezoelectric layer of the high impedance part. The above is the same as the configuration in FIG. The difference from the configuration of FIG. 1 is that the thickness of the piezoelectric layer in the low impedance portion is changed.

The operation of the piezoelectric transformer configured as described above will be described below. The lumped constant approximation equivalent circuit near the resonance frequency of the present piezoelectric transformer is as shown in FIG.

By changing the thickness of the piezoelectric layer of the output section, the values of A21 and A22 and the output capacitances Cd2-1 and Cd2-1 are obtained.
2-2 can be changed. As described above, it is possible to obtain a piezoelectric transformer in which the external electrodes in the low-impedance portion are adapted to a load even when the upper and lower main surfaces have different loads.

In the piezoelectric transformer of this embodiment, as in the first embodiment, since each layer of the output section is thinner than the thickness of the input section, the force coefficient A1 is larger than A21 and A22. Boosted by two equivalent ideal transformers.

Further, even when only one output is required in the piezoelectric transformer of this configuration, it is needless to say that the output can be controlled and the piezoelectric transformer can be driven by connecting a control load to one output. No.

The configuration of the input unit is the same as that of FIG.
As shown in FIG. 4, this piezoelectric transformer also has the same structure as in the first embodiment.
When the input unit has a laminated structure, the layer thickness per layer can be made smaller than the respective layer thicknesses of the output unit, and A1 can be made smaller than A21 and A22.

[0049]

As described above in detail, the piezoelectric transformer of the present invention is small and can generate a high voltage, and a plurality of output voltages can be obtained with one piezoelectric transformer.

In addition, there is an advantage that the reliability of the portion for taking out the external connection terminal is high.

[Brief description of the drawings]

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

FIG. 2 is a lumped parameter equivalent circuit diagram of the piezoelectric transformer of the present invention.

FIG. 3 is a diagram showing a displacement distribution and a stress distribution of a rod-shaped vibrator in a second mode of longitudinal longitudinal vibration.

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

FIG. 5 is a sectional structural view of a high impedance portion of the piezoelectric transformer.

FIG. 6 is a perspective view showing a structure of a piezoelectric transformer according to a second embodiment of the present invention.

FIG. 7 is a perspective view showing another structure of the piezoelectric transformer according to the second embodiment of the present invention.

FIG. 8 is a perspective view showing a structure of a piezoelectric transformer according to a third embodiment of the present invention.

FIG. 9 is a sectional structural view of a low impedance portion of the piezoelectric transformer.

FIG. 10 is a perspective view showing the structure of a piezoelectric transformer according to a fourth embodiment of the present invention.

FIG. 11 is a sectional structural view of a low impedance portion of the piezoelectric transformer.

FIG. 12 is a lumped constant equivalent circuit diagram of the piezoelectric transformer.

FIG. 13 is a perspective view showing the structure of a piezoelectric transformer according to a fifth embodiment of the present invention.

FIG. 14 is a perspective view showing another structure of the piezoelectric transformer according to the fifth embodiment of the present invention.

FIG. 15 is a perspective view showing the structure of a Rosen-type piezoelectric transformer as an example of a conventional piezoelectric transformer.

[Description of Signs] 111 High impedance section 112 Low impedance section 11 External terminal 12U, 12D, 13U, 13D External electrode 14, 15 Piezoelectric layer 16 Internal electrode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiyuki Asahi 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. 72) Inventor Kawa Osamu Osamu 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (6)

[Claims] 1. A low-impedance portion including a plurality of piezoelectric layers each of which is polarized in a thickness direction, an internal electrode interposed between the plurality of piezoelectric layers, and a thickness equal to the thickness of the low-impedance portion. In a piezoelectric transformer, a high-impedance portion composed of a single-layer piezoelectric layer polarized in the direction is integrally formed along the longitudinal direction, and external electrodes are provided on both surfaces of the low-impedance portion and both surfaces of the high-impedance portion. A piezoelectric transformer, wherein at least one of the external electrode and the internal electrode of the low impedance section is connected to an external connection terminal. 2. A low-impedance portion comprising a plurality of piezoelectric layers each of which is polarized in a thickness direction, an internal electrode interposed between the plurality of piezoelectric layers, and each layer having the same thickness as the low-impedance portion. A plurality of piezoelectric layers polarized in the thickness direction, and a high impedance portion composed of internal electrodes interposed between the plurality of piezoelectric layers are integrally formed along the longitudinal direction, and both surfaces of the low impedance portion are formed. And a piezoelectric transformer having external electrodes provided on both surfaces of the high impedance portion, wherein the external electrode and at least one of the internal electrodes of the low impedance portion or the high impedance portion are connected to an external connection terminal. Trance. 3. The size of external electrodes provided on both surfaces of a low impedance portion is different from each other.
The described piezoelectric transformer. 4. The piezoelectric transformer according to claim 1, wherein the thickness of the piezoelectric layer of each layer of the low impedance portion is different. 5. When the length of the piezoelectric transformer in the longitudinal direction is L, the external connection terminal of the low impedance portion or the high impedance portion is L from one end or the other end.
2. The device according to claim 1, wherein the second position is arranged at a position of / 4.
3. The piezoelectric transformer according to any one of claims 1 to 2. 6. The method for driving a piezoelectric transformer according to claim 1, wherein the piezoelectric transformer is driven at a resonance frequency in a longitudinal longitudinal vibration secondary mode in which one wavelength is equal to the total length L of the piezoelectric transformer. A method for driving a piezoelectric transformer, comprising: