JPH11145528A - Piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively provide a piezoelectric transformer element in a structure that has a high boost ratio and efficiency, is driven in a half- wavelength mode, and does not generate a fall-wavelength mode. SOLUTION: In a piezoelectric transformer that is provided with a drive part region which is polarized in a thickness direction with input electrodes 11 and 12 at the center of a long-plate shaped piezoelectric body 10 and a generation part region polarized in a longer direction with an output electrode 13 on one end face in a longer direction and is not provided with an output electrode on the other end face in the longer direction, the ratio (a ratio of L2/L1) of a total length L1 in the longer direction to a length L2 of the drive part is set to 15-35%.

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 a power converter such as an inverter for a backlight of a liquid crystal display or a DC-DC converter.

[0002]

2. Description of the Related Art Generally, in a liquid crystal display, a backlight system in which a discharge tube such as a cold-cathode tube is disposed on the back and side surfaces of a liquid crystal display is mainly used because the liquid crystal itself does not emit light.

[0003] In order to drive this discharge tube, an AC high voltage of several hundred volts or more is required, depending on the length and diameter of the discharge tube itself. As a method of generating the AC high voltage, a discharge tube and an operating device using a piezoelectric transformer are disclosed in Japanese Patent Laid-Open No. 5-113578. Since the piezoelectric transformer has a very simple structure as compared with the wire-wound transformer, the piezoelectric transformer can be reduced in size, thickness, and cost. The principle and characteristics of this piezoelectric transformer are disclosed in “Electronic Ceramics”, July 1971, “Characteristics and Applications of Piezoelectric Transformers” published by Gakusensha.

[0004] As an example of a piezoelectric transformer, C.M. A. FIG. 11 shows a Rosen-type piezoelectric transformer announced by Rosen. The configuration of the Rosen-type piezoelectric transformer will be described with reference to FIG. 11. Reference numeral 2 denotes a plate-shaped piezoelectric ceramic element made of, for example, lead zirconate titanate (PZT). A pair of input electrodes 4 and 5 provided by, for example, silver baking is formed on the upper and lower surfaces, and an output electrode 6 is formed on the right end surface in the same manner. Then, the left half driving section of the ceramic element 2 is polarized in the thickness direction, and the right half power generation section is polarized in the longitudinal direction.

In the piezoelectric transformer thus formed, when an AC voltage having substantially the same frequency as the mechanical resonance frequency in the longitudinal direction of the ceramic element 2 is applied between the input electrodes 4 and 5 from the AC voltage source 8, this ceramic The element 2 generates a strong mechanical vibration in the longitudinal direction, whereby electric charges are generated by the piezoelectric effect in the right half of the power generation unit, and an output voltage Vo is generated between the output electrode 6 and one of the input electrodes, for example, the input electrode 5. . Basically, as shown in FIG. 12, the vibration mode includes a half-wavelength mode (λ / 2 mode in the figure) that resonates at a half wavelength in the longitudinal direction and a full-wavelength mode (λ in the figure) that resonates at one wavelength. λ mode).

[0006]

To reduce the size of the piezoelectric transformer element, it is necessary to drive it in a half-wave mode. However, when driven by a distorted wave in the half-wave mode, there is a problem that the output is distorted due to the mixture of the two vibration modes because the second harmonic corresponds to the full-wave mode. As a piezoelectric transformer in which no full-wavelength mode occurs, a center drive type piezoelectric transformer is known. FIG. 13 shows the structure of a center drive type piezoelectric transformer element. The structure has a driving part polarized in the thickness direction in the center part, and a power generation part polarized in the longitudinal direction on both sides of the driving part. The piezoelectric transformer element having this structure is characterized in that the structure is simple, the output impedance is high, and since no full-wavelength mode is generated, distortion waves are hardly generated.

However, the structure of the piezoelectric transformer element of the center drive type requires the formation of input / output electrodes on the upper and lower surfaces and both end surfaces, and has a problem that the number of electrode forming steps increases and the number of manufacturing steps increases. .

The present invention focuses on the above problems,
An object of the present invention is to provide an inexpensive piezoelectric transformer element having a high boosting ratio, high efficiency, and a structure that is driven in a half-wave mode and does not generate a full-wave mode.

[0009]

According to the present invention, there is provided a drive section region provided with an input electrode in the center of a long plate-shaped piezoelectric body and polarized in the thickness direction, and one side of the long plate-shaped piezoelectric body in the longitudinal direction. An output electrode provided in the vicinity of an end surface of the piezoelectric element, and a power generation unit region polarized in the longitudinal direction by providing an output electrode, and the power generation unit region is formed only on one side of the piezoelectric body present on both sides of the drive unit region in the central portion. It is a piezoelectric transformer. Further, the present invention provides a method of manufacturing the piezoelectric device according to the present invention, in which the ratio (L2)
/ L1) is 15 to 35%. Further, according to the present invention, the piezoelectric transformer is a piezoelectric transformer including a laminated body of piezoelectric sheets provided with an input electrode in a central portion.

[0010]

FIG. 1 is a perspective view of an embodiment according to the present invention. In this embodiment, input electrodes 11 and 12 are provided on the upper and lower surfaces of a central portion of a long plate-shaped piezoelectric body 10, and an output electrode 13 is provided on one end surface. The input electrodes 11, 1
The space between the two is polarized as shown in FIG. 1 to form a drive unit. Further, between the input electrodes 11, 12 and the output electrode 13,
It is polarized as shown in FIG. 1 and constitutes a power generation unit.
The output electrode 13 is formed only on one end surface of the long plate-shaped piezoelectric body 10.

The total length of the piezoelectric transformer in the longitudinal direction is represented by L1.
And the load step-up ratio Vo / Vi and L in the half-wavelength mode of the central drive type piezoelectric transformer when the length of the drive unit is L2.
FIG. 2 shows the relationship between L2 / L1 and FIG. 3 shows the relationship between efficiency and L2 / L1. FIGS. 2 and 3 also show, as comparative examples, cases where output electrodes are formed at both ends. The piezoelectric body 10 has a size of 20 mm × 5 mm × 1.
33 mm (height). Regarding the boost ratio, the embodiment of the present invention can always obtain a higher boost ratio than the comparative example even when L2 / L1 changes. And, as L2 / L1 is larger, a higher boost ratio can be obtained. On the other hand, as for the efficiency, the smaller the ratio L2 / L1, the higher the efficiency can be obtained. When the ratio L2 / L1 is 35% or less, the same efficiency as the comparative example is obtained. from this result,
When L2 / L1 is 15 to 35%, a high voltage step-up ratio and an efficient piezoelectric transformer can be obtained. In addition, L2 /
When L1 is less than 15%, the boost ratio is small, and when it is more than 35%, the efficiency is deteriorated.

Next, another embodiment of the piezoelectric transformer according to the present invention will be described. This embodiment is a laminated piezoelectric transformer having a driving unit having a laminated structure. FIG. 4 is an explanatory diagram, and FIG.
Shown in Since the input voltage Vi is applied to each of the stacked thin layers in the drive unit of the multilayer piezoelectric transformer, the step-up ratio is increased by about the number of layers as compared with the single-plate type. The manufacturing method of the laminated piezoelectric transformer is as follows. A green sheet of PZT ceramics is manufactured by a doctor blade method, and the internal electrodes 27 and 28 are printed on a part of the green sheet by a screen printing method. It is laminated and pressed and sintered. Thereafter, cutting and polishing are performed, and the input external electrodes 21 and 22 and the output electrode 25 are provided by baking silver. The internal electrode 27 is connected to the external electrode 21, and the internal electrode 28 is connected to the external electrode 22. Then, polarization processing is performed in the thickness direction of the drive unit and in the longitudinal direction of the power generation unit to complete the process. In the half-wave mode, the center of the piezoelectric body in the longitudinal direction has the smallest vibration amplitude. Therefore, by providing the external electrodes 21 and 22 at this position, the reliability of the lead wire connected to the external electrode can be improved. . In this case, the lead wire is taken out from the side of the piezoelectric transformer. Here, although the upper and lower ends of the driving unit are not polarized, they are dummy layers. However, electrodes are provided on the upper and lower surfaces of the driving unit, and the external electrodes 22 and 2 are respectively provided.
By connecting to 1, the dummy layer can be eliminated.

FIG. 6 is an explanatory view of another embodiment of the laminated piezoelectric transformer of the present invention. The output electrode 35 extends from the end face to the side face of the piezoelectric transformer. By attaching the lead wire to the portion where the output electrode extends in this way, it is not necessary to attach the lead wire from the output electrode to the end face where vibration is maximum, and the vibration of the piezoelectric transformer itself due to attaching the lead wire This has the effect of suppressing the occurrence of disconnection of the lead wire attachment portion due to suppression of vibration and vibration.
The extension of the output electrode may be provided on the upper surface of the piezoelectric transformer.

FIG. 7 is an explanatory view of another embodiment of the laminated piezoelectric transformer of the present invention. FIG. 8 is a plan view of the laminated piezoelectric sheets. In this embodiment, the input electrodes 37 and 38 are printed on the central portion of the piezoelectric sheet 33, and the output electrodes 34 are printed on one end surface in the longitudinal direction. The external electrodes 31 and 32 of the input electrodes 37 and 38 are formed on the side surfaces, and the external electrodes 36 of the output electrodes 34 are formed on the side surfaces. According to this embodiment, it is possible to form the external electrodes of the input electrode and the output electrode only on two sides, and it is not necessary to form the output electrode 35 as shown in FIG. .

FIG. 9 is an explanatory view of another embodiment of the laminated piezoelectric transformer of the present invention. FIG. 10 is a plan view of the stacked piezoelectric sheets. In this embodiment, the input electrodes 37 and 38 are printed on the central portion of the piezoelectric sheet 33, and the output electrodes 34 are printed on one end surface in the longitudinal direction. The external electrodes 31 and 32 of the input electrodes 37 and 38 are formed on the side surfaces, and the external electrodes 36 of the output electrodes 34 are formed on the side surfaces. According to this embodiment,
The external electrodes of the input electrode and the output electrode can be formed only on one side.

According to the embodiment of the present invention, the output electrode is formed only on one end face side, so that the electrode forming step can be further reduced as compared with the case where output electrodes are formed on both end faces. And cost reduction can be achieved. Further, in the laminated structure, a structure having only two sides or only one side is also possible.

In the case where output electrodes are formed on both end surfaces when a high-voltage output is extracted, it is necessary to wire the piezoelectric transformer element and the vicinity of the input and ground lines, and it is necessary to consider the insulation distance and the like. However, according to the present invention, the high-voltage output is taken out from only one end face, so that the design becomes easy.

[0018]

According to the present invention, in the center drive type piezoelectric transformer, by forming the output electrode only on one end surface, it is possible to obtain a piezoelectric transformer having a high boosting ratio and high efficiency. In addition, the cost can be reduced by reducing the number of electrodes, and the high-voltage output is taken out from only one end surface, so that the structural design becomes easy.

[Brief description of the drawings]

FIG. 1 is a perspective view of an embodiment according to the present invention.

FIG. 2 shows the boost ratio and L2 / L of the example according to the present invention and the comparative example.
It is a graph which shows the relationship of L1.

FIG. 3 shows the efficiency and L2 / L of the example according to the present invention and the comparative example.
1 is a graph showing the relationship of FIG.

FIG. 4 is a perspective view of another embodiment according to the present invention.

FIG. 5 is a sectional view of the embodiment of FIG.

FIG. 6 is a perspective view of another embodiment according to the present invention.

FIG. 7 is a perspective view of another embodiment according to the present invention.

8 is a plan view of the piezoelectric sheet of the embodiment shown in FIG. 7;

FIG. 9 is a perspective view of another embodiment according to the present invention.

FIG. 10 is a plan view of the piezoelectric sheet of the embodiment shown in FIG. 9;

FIG. 11 is a perspective view of a conventional example.

FIG. 12 is an explanatory diagram of a vibration mode of a piezoelectric transformer.

FIG. 13 is a perspective view of another conventional example.

[Explanation of symbols]

 Reference Signs List 10 piezoelectric body 11, 12 input electrode 13, 25, 34, 35 output electrode 20, 30 laminated piezoelectric transformer 21, 22, 31, 32 external electrode for input 27, 28, 37, 38 internal electrode (input electrode) 33 piezoelectric Body sheet 36 Output external electrode

Claims (3)

[Claims] 1. A drive section region provided with an input electrode in the center of a long plate-shaped piezoelectric body and polarized in the thickness direction, and an output electrode provided near one end face in the longitudinal direction of the long plate-shaped piezoelectric body. And a power generation unit region polarized in the longitudinal direction, wherein the power generation unit region is formed on only one side of the piezoelectric body present on both sides of the central drive unit region. 2. A total length L of the long plate-shaped piezoelectric body in a longitudinal direction.
1 and the ratio of the length L2 of the driving unit (the ratio of L2 / L1) is 1
2. The piezoelectric transformer according to claim 1, wherein the amount is 5 to 35%. 3. The piezoelectric transformer according to claim 1, wherein the piezoelectric transformer is formed of a laminate of piezoelectric sheets provided with an input electrode at a central portion.