JP4077083B2 - Input region structure of piezoelectric transformer element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an input region structure of a piezoelectric transformer element, for example, an input region structure of a piezoelectric transformer element suitable for use in, for example, lighting a cold cathode tube.
[0002]
[Prior art]
A cold cathode tube is generally used as a backlight of a liquid crystal display such as a notebook personal computer. While this cold cathode tube requires a high voltage of about 1 kV during lighting, it requires a voltage of about several hundred volts during continuous lighting, and is continuously lit at an extremely low voltage compared to the voltage required during lighting. be able to. Since the operation characteristics of such a cold cathode tube are similar to the operation characteristics of the piezoelectric transformer element, in recent years, a step-up module including the piezoelectric transformer element has been used as a power source for the cold cathode tube.
[0003]
As a piezoelectric transformer element, for example, a Rosen type piezoelectric transformer element as shown in FIG. 5 is generally widely known.
[0004]
FIG. 5 is a perspective view showing a general Rosen-type piezoelectric transformer element. In the figure, the piezoelectric transformer element 106 has a strip shape. The left half of the figure is an input area, and the right half of the figure is an output area. External electrodes 101 and 102, which are input electrodes for applying an input voltage, are provided above and below the input region, and external electrodes 103, which are output electrodes for extracting a boosted AC voltage, are provided on the end surface of the output region. Yes. When an AC voltage (input voltage) having a resonance frequency obtained from the material and length of the piezoelectric transformer element 106 is applied between the external electrodes 101 and 102, the piezoelectric transformer element 106 causes mechanical vibration in the longitudinal direction. Resonates. By this mechanical vibration, a boosted AC voltage is generated between the external electrode 103 and either the external electrode 101 or the external electrode 102 as a common ground electrode on the input side and the output side. To do. Here, the step-up ratio, which is the ratio between the output voltage and the input voltage, is proportional to the ratio between the distance between the output electrodes and the distance between the input electrodes.
[0005]
Conventionally, a single-plate type piezoelectric transformer element as shown in FIG. 5 has been used as the piezoelectric transformer element. However, in a booster module having a single-plate type piezoelectric transformer element, the boosting ratio is only about 10 times. Therefore, in order to light a cold cathode tube for a notebook personal computer, it is necessary to further include a step-up winding transformer in the previous stage. Therefore, by reducing the distance between the electrodes of the piezoelectric layer in the input region, that is, by forming a piezoelectric transformer element having a structure in which a plurality of thin piezoelectric bodies and internal electrodes are laminated, In comparison, the step-up ratio is high, and attempts have been made to eliminate the need for the previous winding transformer.
[0006]
In such a laminated piezoelectric transformer element, it is essential to electrically connect internal electrodes in the input region. For example, in Japanese Patent Laid-Open No. 7-302938, each internal region in the input region In order to make electrical connection between the electrodes, a method of providing electrodes on the side surfaces or end surfaces of the piezoelectric transformer element has been proposed. Japanese Patent Application No. 8-52553 proposes a method of electrically connecting each internal electrode in the input region with a layer indirect conductor provided inside the piezoelectric transformer element.
[0007]
And after taking conduction between each internal electrode by such a method, as an electrode (input electrode) for applying an input voltage to these internal electrodes and two external electrodes for polarizing the piezoelectric transformer element, For example, Japanese Patent Laid-Open No. 10-41559 proposes a piezoelectric transformer element in which external electrodes are provided on two surfaces having the largest area among a plurality of surfaces constituting the outer shape of the piezoelectric transformer element.
[0008]
Further, the applicant of the present application has proposed a piezoelectric transformer element in which the two external electrodes are provided on one of the two surfaces having the largest area in the preceding Japanese Patent Application Laid-Open No. 10-84143. This piezoelectric transformer element by the applicant of the present application is effective in reducing the thickness when housed in a case, and since two input electrodes are provided on any surface having the largest area, the input electrodes In the manufacturing process of soldering, the piezoelectric transformer element does not need to be turned upside down, and is excellent in mountability.
[0009]
[Problems to be solved by the invention]
However, in the piezoelectric transformer element by the applicant of the present application, if the distance between the two input electrodes having the above-described configuration is too short in the course of further research, irregular vibration is added to the vibration of the piezoelectric transformer element. It has been found that the boosting efficiency is reduced by vibration.
[0010]
Accordingly, an object of the present invention is to provide an input region structure of a piezoelectric transformer element that is excellent in mountability and boosting efficiency.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the input region structure of the piezoelectric transformer element according to the present invention is characterized by the following configuration.
[0012]
That is, an input region structure of a piezoelectric transformer element having a laminated structure having an input region polarized in the thickness direction and formed with an input electrode and an output region polarized in the longitudinal direction and formed with an output electrode. ,
The input region has a plurality of internal electrodes as input electrodes arranged between layers of a plurality of piezoelectric bodies, and at least first and second external electrodes formed on end faces in the longitudinal direction of the piezoelectric transformer element. And
The plurality of internal electrodes are alternately connected to each other by the first or second external electrode, and the first and second external electrodes are arranged adjacent to each other via the piezoelectric body. It is characterized by being formed at least 5 times the distance between the internal electrodes.
Thereby, an input region structure of a piezoelectric transformer element excellent in mountability and boosting efficiency is realized.
[0013]
In addition, for example, the first and second external electrodes are further extended to one of the two surfaces having the largest area among the plurality of surfaces constituting the outer shape of the piezoelectric transformer element. Alternatively, the plurality of internal electrodes may be included in the piezoelectric transformer element.
[0014]
In any of the above cases, the output electrode may be formed on the end face in the longitudinal direction of the piezoelectric transformer element on the output region side.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of a piezoelectric transformer element according to the present invention will be described in detail with reference to the drawings.
[0016]
In the following description, the end face in the longitudinal direction of the piezoelectric transformer element refers to a surface that does not include a position that becomes a vibration node when the element is driven in a λ mode, a λ / 2 mode, or the like.
[0017]
In this embodiment, the piezoelectric transformer element proposed in Japanese Patent Application No. 10-18749 (not disclosed at the time of filing this application) preceded by the applicant of the present application, that is, two elements in the longitudinal direction of the element. Based on a piezoelectric transformer element capable of driving and supporting the element at the end face, one of the two faces having the largest area among the plurality of faces constituting the outer shape of the element (hereinafter referred to as a book) In the embodiment, a piezoelectric transformer element in which two input electrodes are extended to the ceiling surface will be described as an example. However, if the piezoelectric transformer element has two input electrodes at least on the end face of the input region, The invention is applicable.
[0018]
FIG. 1 is a perspective view showing a piezoelectric transformer element as one embodiment of the present invention. FIG. 2 is a front view of the piezoelectric transformer element of FIG. 3 is a cross-sectional view taken along the line AA ′ of FIG.
[0019]
As shown in FIGS. 1 to 3, in the present embodiment, external electrodes (input electrodes) 1 and 2 for applying an input voltage are provided from the longitudinal end face of the input region of the piezoelectric transformer element 6 to the ceiling surface. It has been. Further, an external electrode (output electrode) 3 for extracting a boosted high voltage is provided on an end face in the longitudinal direction of the output region of the element. Due to such a structure, the piezoelectric transformer element 6 in this embodiment is effective in reducing the thickness when housed in a case, and the front and back sides of the piezoelectric transformer element are covered in the manufacturing process of soldering the external electrodes 1 and 2. There is a first feature that there is no need to turn it over and it is excellent in mountability.
[0020]
Since the structure of the internal electrode in the input region has been proposed in the above Japanese Patent Application No. 10-187749, a detailed description thereof will be omitted here, but here it is outlined along the manufacturing process of the piezoelectric transformer element 6. First, in the input region of the piezoelectric transformer element 6, internal electrodes 1a and 2a made of silver / palladium paste of Ag / Pd = 70/30 are formed in a thin plate shape having a thickness after firing of approximately 100 micrometers. A plurality of layers are alternately stacked with the piezoelectric green sheets sandwiched therebetween, and have an enclosed structure. The internal electrodes 1a and 2a have projections for connecting to the external electrodes 1 and 2, respectively. In addition, each internal electrode is good also as a structure exposed to the side surface instead of the structure included in a piezoelectric transformer element.
[0021]
Next, the piezoelectric body in which the internal electrodes 1a and 2a and the piezoelectric green sheet before firing are laminated is fired. Next, external electrodes 1 to 3 are printed on the fired piezoelectric body with a silver paste, and a conductor is baked at about 850 ° C. Then, the piezoelectric transformer element 6 is obtained by polarizing the piezoelectric body by a general method.
[0022]
Here, the second feature of the piezoelectric transformer element 6 in the present embodiment will be described.
[0023]
In this embodiment, when printing the external electrodes 1 and 2 on the fired piezoelectric body, the distance L between the two external electrodes is separated by at least 5 times the interlayer distance D between the internal electrodes 1a and 2a. To print. When the distance L is shorter than this, the polarization regions that are not separated from each other are generated on the surfaces of the adjacent portions of the external electrodes 1 and 2 during polarization. That is, in the input region of the piezoelectric body, although the piezoelectric body originally wants to be polarized uniformly in the thickness direction (vertical direction in FIG. 3), it cannot be sufficiently polarized in that direction. Later, when the piezoelectric transformer element 6 is actually driven by applying an input voltage to the external electrodes 1 and 2, an unnecessary vibration force is generated in a direction perpendicular to the direction in which the element is to resonate in the input region. This unnecessary vibration force becomes noise and inhibits the resonance state, and as a result, the boosting efficiency of the piezoelectric transformer element 6 is reduced.
[0024]
FIG. 4 is a diagram showing the boosting efficiency when driving a piezoelectric transformer element in which the relationship between the distance between the input electrodes and the distance between the internal electrodes is different. When driving each element, a load of 50 kΩ is connected. And driven with an input voltage of 9.0 V and an output of 3 W.
[0025]
As shown in the figure, it can be seen that when the distance L between the external electrodes 1 and 2 is 5 times or more the distance D between the internal electrodes, the boosting efficiency becomes the highest.
[0026]
Here, the relationship between the distance from the end face of the external electrodes 1 and 2 on the ceiling surface and the distance L will be described. The longer the length from the end face of the external electrodes 1 and 2, the greater the width of the element between the external electrodes. The pressurization rate decreases under the influence of the direction polarization. However, according to the experiment by the applicant of the present application, the relationship between the length of the external electrode on the ceiling surface and the boosting efficiency does not change so much as the distance L increases, and when L / D is greater than 5, It has been experimentally found that there is a relationship that the boosting efficiency does not change even if the length of the external electrode is changed, and that the relationship is substantially the same as in the present embodiment.
[0027]
In the above-described embodiment, the piezoelectric transformer element 6 in which the external electrodes 1 and 2 are extended to the ceiling surface is described as an example. However, the piezoelectric transformer element in which the external electrodes 1 and 2 are provided only on the end face on the input side. In this case, the relationship between the distance L between the external (input) electrodes and the distance D between the internal electrodes is the change in boosting efficiency due to L / D compared to the case where the external electrodes extend to the ceiling surface. However, when L / D is smaller than 5, there is a relationship that the boosting efficiency slightly decreases, and it has been experimentally found that the relationship is substantially the same as that of the present embodiment.
[0028]
In the above-described embodiment, the case where the thickness of the fired external electrodes 1 and 2 is 5 μm has been described as an example. Here, the thicknesses of the internal electrodes 1a and 2a and the distance D between the internal electrodes are set to the same conditions (values) as in the above embodiment, and the distance L when the thicknesses of the external electrodes 1 and 2 are changed. Explaining the relationship, even when the thicknesses of the external electrodes 1 and 2 are changed in the range of 1 to 20 μm, there is almost no influence on the polarization state of the piezoelectric body between the external electrodes. Does not need to be considered. Therefore, there is almost no influence on the boosting efficiency due to the difference in thickness between the external electrodes 1 and 2, and the result of FIG. 4 can be applied.
[0029]
In the present embodiment, the width of each of the external electrodes 1 and 2 is set to a width that does not reach the edge portion in the width direction of the piezoelectric transformer element 6 as shown in FIG. 2, but is not limited to this. If the relationship between the distance L between the external electrodes and the distance D between the internal electrodes is satisfied, the width of the external electrode has a width that reaches the end face in the width direction of the piezoelectric transformer element 6. Also, the experimental results of FIG. 4 can be applied.
[0030]
As described above, according to the piezoelectric transformer element 6 described above, it is needless to say that the mountability is excellent, and a piezoelectric transformer element having further excellent boosting efficiency can be realized.
[0031]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an input region structure of a piezoelectric transformer element that is excellent in mountability and boosting efficiency.
[0032]
[Brief description of the drawings]
FIG. 1 is a perspective view showing a piezoelectric transformer element according to a first embodiment of the present invention.
2 is a front view of the piezoelectric transformer element of FIG. 1. FIG.
3 is a cross-sectional view taken along line AA ′ of FIG.
FIG. 4 is a diagram showing boosting efficiency when driving a piezoelectric transformer element in which the relationship between the distance between the input electrodes and the distance between the internal electrodes is different.
FIG. 5 is a perspective view showing a general Rosen-type piezoelectric transformer element.
[Explanation of symbols]
1-3, 101-103: External electrodes,
1a, 2a: internal electrodes,
6, 106: Piezoelectric transformer element,

Claims (4)

An input region structure of a piezoelectric transformer element of a laminated structure having an input region polarized in the thickness direction and formed with an input electrode, and an output region polarized in the longitudinal direction and formed with an output electrode,
The input region has a plurality of internal electrodes as input electrodes arranged between layers of a plurality of piezoelectric bodies, and at least first and second external electrodes formed on end faces in the longitudinal direction of the piezoelectric transformer element. And
The plurality of internal electrodes are alternately connected to each other by the first or second external electrode, and the first and second external electrodes are arranged adjacent to each other via the piezoelectric body. An input region structure of a piezoelectric transformer element, wherein the input region structure is formed at least 5 times apart from a distance between internal electrodes. The first and second external electrodes are further extended to one of the two surfaces having the largest area among the plurality of surfaces constituting the outer shape of the piezoelectric transformer element. The input region structure of the piezoelectric transformer element according to claim 1. The input region structure of the piezoelectric transformer element according to claim 1, wherein the plurality of internal electrodes are included in the piezoelectric transformer element. The input region structure of the piezoelectric transformer element according to any one of claims 1 to 3, wherein the output electrode is formed on an end face in a longitudinal direction of the piezoelectric transformer element on the output region side.

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