JP2001156353A - Piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric transformer having an electrode structure which can be manufactures at a high yield by preventing the crack of a piezoelectric ceramics which is easy to occur at polarizing in the manufacturing process for a piezoelectric transformer. SOLUTION: A laminated piezoelectric transformer is provided where a piezoelectric ceramics layer which is approximately square plate and an approximately square internal electrode are alternately laminated, utilizing the resonance mode of a piezoelectric ceramics which is approximately square plate. Here, related to one or both of input part and output part, all corners, except one corner, of the approximately square internal electrode are cut out, with a remaining corner used as a connection part with an external electrode. The internal electrode is oriented so that the connection part does not overlap between input and output or between polarities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer mainly for voltage conversion, and more particularly to a piezoelectric transformer suitable for an AC adapter or a DC-DC converter.

[0002]

2. Description of the Related Art Recently, the demand for a piezoelectric transformer used as a power source for a liquid crystal backlight of a notebook personal computer has been increasing.
In order to simultaneously increase the DC voltage of a dry cell from a DC voltage to a high voltage of several hundred volts and to achieve a reduction in thickness, conventional electromagnetic inverters have several problems in terms of shape and efficiency. is there. On the other hand, AC adapters and DC-DC converters using piezoelectric transformers are characterized by their small size, low profile, and high efficiency, and their practical use is being developed.

Meanwhile, in order to keep the efficiency of the piezoelectric transformer high, impedance matching with a load is important. The inverter power supply, which is boosted to a high voltage of several hundred volts and connected to a load of several tens of kΩ or more, is rather special as a form of use of the piezoelectric transformer, and the situation of impedance matching when applied to other general power supplies Is as follows. As an example, the case of various portable electronic devices connected to the output unit of the AC adapter will be described. Their input impedance is about several Ω to several tens Ω. Then, the output impedance R of the piezoelectric transformer is obtained from the angular frequency ω (= 2πf, where f is the frequency) and the braking capacitance _Cd2 on the output side as shown in Expression (1). R = 1 / ωC _d2 (1)

For example, when R = 60Ω and f = 120 kHz, C _d2 = 22 nF. The output-side braking capacity of the piezoelectric transformer used for the power supply for liquid crystal backlight is several tens of p
In this case, the braking capacity is required to be three orders of magnitude larger than F. The laminated piezoelectric transformer utilizing the spreading vibration mode of the piezoelectric ceramic square plate is one of the structures expected to be applied to the above-mentioned applications having relatively small load impedance.

FIGS. 3 to 5 show an example of this piezoelectric transformer. FIG. 3 is a plan view showing the shape of the internal electrode, and FIG.
FIG. 5 is a schematic cross-sectional view in which a vertical direction is enlarged to show a state in which an internal electrode and a piezoelectric ceramic plate are laminated, and FIG. 5 is an external perspective view.

In FIG. 3, FIG. 3A shows an internal electrode of one polarity for output, FIG. 3B shows an internal electrode of the other polarity for output, and FIG. 3C shows one internal electrode for input. FIG. 3 (d) shows an internal electrode of the other polarity for input. Numeral 31 indicates the shape of the internal electrode, and numeral 32 indicates a part of the piezoelectric ceramic plate. That is, a piezoelectric ceramic plate in which the direction of the electrode extraction portion differs by 90 ° with respect to the input portion and the output portion, and a piezoelectric ceramic plate in which the orientation differs by 180 ° with the polarity of each of the input portion and the output portion are laminated. It has a structure that has been done.

In FIG. 4, reference numeral 12 denotes an input section, 13 denotes an output section, 14 denotes a ceramic insulating layer, and 15a, 15b
Denotes internal electrodes for input, and 16a and 16b denote internal electrodes for output.

In FIG. 5, a portion 23 surrounded by a two-dot chain line indicates a polarization region, 21a indicates one of the side external electrodes for output, and 22b indicates one of the side external electrodes for input.

[0009]

Generally, when laminating and sintering a piezoelectric ceramic plate and an internal electrode, the piezoelectric characteristics of a portion of the piezoelectric ceramic that contacts the internal electrode and a portion of the piezoelectric ceramic that does not contact the internal electrode are increased. There is a phenomenon in which a difference easily occurs, and as a result, a piezoelectric inactive portion appears.

In the piezoelectric transformer having the above-mentioned shape, in the above-described electrode structure, when a voltage is applied during the polarization processing of the piezoelectric ceramic, the presence of the piezoelectric inactive portion causes the periphery of the electrode take-out portion to be removed. It was often observed that an electric field was concentrated on the surface, stress was concentrated on that portion, and the piezoelectric ceramics were cracked.

Accordingly, the present invention is to provide a piezoelectric transformer having an electrode structure capable of preventing cracking of a piezoelectric ceramic which is liable to occur at the time of polarization processing in a manufacturing process of the piezoelectric transformer and capable of being manufactured at a high yield rate. It is an issue.

[0012]

In order to solve the above problems, according to the present invention, as shown in FIGS. 1 (a) to 1 (d), one corner of a square is left and the other corner is left. An internal electrode with a cutout was adopted, and the remaining square corner was connected to an external electrode. 1 (a) is an internal electrode of one polarity for output, FIG. 1 (b) is an internal electrode of the other polarity for output, FIG. 1 (c) is an internal electrode of one polarity for input,
FIG. 1D shows an internal electrode of the other polarity for input. By laminating the internal electrodes of such a shape with the piezoelectric ceramic plate in such a direction, the polarization is regarded as the region except for the corners of the square sandwiched between the bipolar electrodes, and is generated when the polarization is performed. The concentrated electric field is limited to only the corners of the square. As a result, stress concentration is reduced, and polarization cracking can be reduced.

That is, the piezoelectric transformer of the present invention is a laminated type piezoelectric transformer using a resonance mode of a square-plate-shaped piezoelectric ceramic and alternately stacking square-plate-shaped piezoelectric ceramic layers and square-shaped internal electrodes. Then, in one or both of the input part and the output part, one of the corners of the square-shaped internal electrode is cut out except one, and the remaining corner is used as a connection part with the external electrode. The orientation of the internal electrodes is determined so that they do not overlap each other during input / output or between polarities.

Further, it is effective to make the shape of the cutout portion of the corner in the internal electrode into an isosceles triangle. Here, the corners of the square plate are chamfered to prevent loss, and even if the corners are made substantially square, the characteristics of the piezoelectric transformer are not significantly affected. In the case of a substantially square plate shape, the shape of the cutout portion is also a substantially isosceles triangle.

[0015]

Embodiments of the present invention will be described with reference to the drawings.

In the shape of the internal electrode shown in FIG. 1, the shape of the notch at the corner of the square is an isosceles triangle,
Its equilateral length is 1/3 to 1/4 of the length of one side of the square
It is practical to do.

Next, the stacking in the thickness direction and the extraction of the electrodes will be described. Since the structure in the thickness direction is common to FIG. 4 referred to when the state of lamination is described in the conventional example,
This diagram will be described with reference to FIG. FIG. 2 is referred to for the side external electrodes.

As shown in FIG. 4, the laminated square plate is divided into two in the thickness direction, one of which is an input unit 12 and the other is an output unit 13, which is located at the center of the boundary between the input and output units. Has a ceramic insulating layer 14 having a thickness of 0.3 mm. Input side internal electrodes 15a and 15b are arranged in the input section, and each of the side external electrodes 1 for input application shown in FIG.
8a, 18b. Similarly, output side internal electrodes 16a and 16b are arranged in the output portion, and are alternately exposed on the side surfaces of every other one and connected to the output extraction side external electrodes 17a and 17b shown in FIG.

FIG. 2 is a perspective view showing the outer shape, the polarization region, and the external electrodes of the piezoelectric transformer of the present invention. The dimension is one side
It has a thickness of 7.6 mm and a thickness of 6.0 mm. A portion 19 surrounded by a two-dot chain line is a polarization region. 17a, 17b, 18a,
18b is a side surface external electrode as already explained.

The polarization process is performed at 165 ° C. for both input and output.
In silicone oil at an electric field strength of 1 kV / mm.

Table 1 shows the rate of occurrence of cracks during polarization in comparison with the conventional example.

[0022]

[Table 1]

The rate of occurrence of cracks is 35% in the conventional example, but is 0% in the example of the present embodiment, which is a significant improvement.

Next, the measurement results of the oscillator constants are shown in Table 2.

[0025]

[Table 2]

As shown in Table 2, the change in the electrode shape hardly affected the oscillator constant.

As described above, by improving the shape of the internal electrode, cracking of the piezoelectric ceramic during polarization could be greatly reduced without substantially changing the oscillator constant.

[0028]

According to the present invention, it is possible to prevent a piezoelectric ceramic from cracking in a piezoelectric transformer polarization process and to manufacture and provide a piezoelectric transformer with a high yield rate.

[Brief description of the drawings]

FIG. 1 is a plan view showing the shape of an internal electrode of a piezoelectric transformer according to the present invention. 1A is a diagram showing an internal electrode of one polarity for output, FIG. 1B is a diagram showing an internal electrode of the other polarity for output, and FIG. 1C is one polarity of an input electrode. FIG. 1D is a diagram showing an internal electrode of the other polarity for input.

FIG. 2 is a perspective view showing an outer shape, a polarization region, and external side electrodes of the piezoelectric transformer of the present invention.

FIG. 3 is a plan view showing the shape of a conventional internal electrode. FIG.
FIG. 3A shows an internal electrode of one polarity for output, and FIG.
FIG. 3B shows an internal electrode of the other polarity for output, and FIG.
FIG. 3C shows an internal electrode of one polarity for input, FIG.
(D) is a diagram showing an internal electrode of the other polarity for input.

FIG. 4 is a schematic cross-sectional view showing a state in which an internal electrode and a piezoelectric ceramic plate are stacked.

FIG. 5 is an external perspective view of a conventional piezoelectric transformer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 Input part 13 Output part 14 Ceramic insulating layer 15a, 15b Input internal electrode 16a, 16b Output internal electrode 17a, 17b Output side external electrode 18a, 18b Input side external electrode 19 Polarized area 21a Output One polarity side external electrode 22b One polarity side external electrode for input 23 Polarized region 31 Internal electrode 32 Piezoelectric ceramic plate

Claims (2)

[Claims] 1. A laminated piezoelectric transformer in which a substantially square plate-shaped piezoelectric ceramic layer and a substantially square-shaped internal electrode are alternately laminated by utilizing a resonance mode of a substantially square plate-shaped piezoelectric ceramic. For one or both of the output sections, cut out one of the corners of the substantially square internal electrode except for the corner, and use the remaining corner as a connection with the external electrode. Alternatively, the piezoelectric transformer is characterized in that the directions of the internal electrodes are determined so that the polarities do not overlap each other. 2. The piezoelectric transformer according to claim 1, wherein a shape of a cutout portion at a corner of the internal electrode is a substantially isosceles triangle.