JPH11340537A - Piezoelectric transformer - Google Patents

Abstract

(57) [Summary] [Problem] To provide a piezoelectric transformer having a structure in which a mounting structure of a piezoelectric transformer is examined and mounting can be efficiently performed, and the mounting can be reduced in size. SOLUTION: The piezoelectric transformer comprises a central drive type piezoelectric transformer element having an input electrode opposed to a central part and output electrodes at both ends, and a protective case holding the element and mounted on a mounting board. And a connection conductor for conducting between output electrodes at both ends of the piezoelectric transformer element.

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 for voltage conversion.

[0002]

2. Description of the Related Art In recent years, power supply circuits such as a backlight inverter and a DC / DC converter for a liquid crystal display using a piezoelectric transformer have been actively studied.
The reason for this is that the adoption of the piezoelectric transformer makes it possible to realize a drastic reduction in size and thickness of the power supply circuit.

[0003] As a piezoelectric transformer for this power supply circuit,
Various driving modes have been proposed, but the smallest one is a piezoelectric transformer driven in a half-wave mode. This is because when driven at the same frequency, the element of the piezoelectric transformer driven in the one-wavelength mode is twice as long as the element driven in the half-wave mode. But,
Conventionally, piezoelectric transformers that have been studied are of a type that is driven in almost one-wavelength mode. The reason for this is that the step-up ratio in the one-wavelength mode is higher than that in the half-wavelength mode by 20 to 30%, the resonance in the one-wavelength mode may occur when driven in the half-wavelength mode, and the holding structure is It was relatively easy.

For example, FIG. 7 shows a Rosen type piezoelectric transformer conventionally well-known as a piezoelectric transformer. In the case of this Rosen type, when it resonates in the half-wave mode, it also resonates strongly in the one-wave mode. Therefore, when a continuous rectangular pulse having a resonance frequency of a half-wave mode is applied as an input waveform, resonance of a single-wave mode is strongly excited in a Rosen-type piezoelectric transformer, and as a result, the output waveform has a half-wave mode. One-wavelength mode is mixed, resulting in significant waveform distortion. In order to prevent this, for example, it is necessary to take measures such as using two switching elements such as FETs to make the input waveform close to a sine wave.

On the other hand, as shown in FIG. 8, in the case of a piezoelectric transformer in which an input electrode is formed at the center of an element and output electrodes are provided at both ends of the element, when driven in a half-wavelength mode, the piezoelectric transformer in a one-wavelength mode Resonance is strongly suppressed. Because, at resonance in the one-wavelength mode, when the right half of the element contracts, the left half of the element must extend. When the input electrodes are formed symmetrically as shown in FIG. 8, even-order resonance modes such as one-wavelength mode are not allowed,
Only odd-order resonance modes such as wavelength and 5 ／ wavelength are allowed. Therefore, if this element (center driving type) is used, even if the piezoelectric transformer is driven with an input waveform having a large number of harmonic components due to one-switch switching, distortion of the output waveform is small.

A piezoelectric transformer driven in the half-wavelength mode and having an input electrode formed in the center is disclosed in
An example described in Japanese Patent No. 60737 is disclosed. This is shown in FIG.

[0007]

According to the conventional center drive type piezoelectric transformer, an input terminal is provided on the side surface at the center, and output terminals are formed on both ends. In the case of this conventional structure, the output terminals that become high voltage are at both ends in the longitudinal direction of the piezoelectric transformer element. Since the high-voltage output terminals are provided at both ends in the longitudinal direction of the piezoelectric transformer element, high-voltage countermeasures are required at both ends. The output terminals at both ends are used by being connected to each other on the mounting board.

For example, FIG. 10 shows a land pattern of a substrate on which the piezoelectric transformer element is mounted. FIG. 10A is a plan view, and FIG. 10B is a rear view. FIG. 10 shows a piezoelectric transformer element 20 (shown by a broken line) housed in a protective case.
Is a printed circuit board 21 on which are mounted lands 22 and 23 to which input electrodes of the piezoelectric transformer element are connected and lands 24 and 25 to which output electrodes are connected. The connection between the output electrodes is made by connecting line 2 to this mounting board.
7, and were connected by a mounting board.

Since the connection lines between the output electrodes of the piezoelectric transformer elements are formed on the mounting substrate, no circuit elements can be mounted on the back surface of the high-voltage connection lines, so that the design has a sufficient space in terms of space. The structure was such that density mounting was not possible. Also, slit holes 26 are formed at three locations for insulation.

In view of the above, an object of the present invention is to examine a mounting structure of a piezoelectric transformer, and to provide a piezoelectric transformer having a structure that can be mounted efficiently and can be reduced in mounting size.

[0011]

SUMMARY OF THE INVENTION The present invention provides a centrally driven piezoelectric transformer element having an input electrode opposed to a central part and output electrodes at both ends, a protective case for holding the element and mounting it on a mounting board. Wherein the protective case is provided with connection conductors for conducting between output electrodes at both ends of the piezoelectric transformer element.

Further, according to the present invention, the piezoelectric transformer element includes:
An input electrode at the center, a laminate of piezoelectric sheets formed with output electrodes at both ends, the input electrodes are alternately connected to the input terminal electrodes on the side surfaces, and the output electrodes are connected to the output terminal electrodes on both side surfaces. Connected, the protection case is electrically connected to the input terminal electrode and the output terminal electrode, and has a metal terminal having a spring property.The piezoelectric transformer element is electrically connected and held by the spring property of the metal terminal. A piezoelectric transformer.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a connection conductor is provided in a protective case, and thereby connection is made to output electrodes provided at both ends of a central drive type piezoelectric transformer element. This eliminates the need to provide a connection line between the output electrodes of the piezoelectric transformer element on the mounting board. This eliminates a connection line between output electrodes serving as a high-voltage line on the mounting substrate, and allows another circuit element to be mounted on the back surface on which the piezoelectric transformer is mounted, thereby enabling high-density mounting. Further, this makes it possible to reduce the size of the inverter circuit on which the piezoelectric transformer is mounted.

FIG. 1 is a perspective view of an embodiment according to the present invention. In this embodiment, the center driving type piezoelectric transformer element 31 is used.
And a lower protective case 32 and an upper protective case 33.

FIG. 2 is a perspective view of the center drive type piezoelectric transformer element 31, and FIG. 3 is an internal structure thereof. This piezoelectric transformer element 31 is configured by laminating piezoelectric green sheets 41 and 42 as shown in FIG. The piezoelectric green sheet 41 has an input electrode 43 formed at the center and output electrodes 45 formed at both ends. The input electrode 43 is formed so as to face one side surface and not reach the opposite side surface. Similarly, the piezoelectric green sheet 42 has an input electrode 44 at the center and output electrodes 45 at both ends. The input electrode 44 is formed so as to face one side opposite to the above, and not to reach the opposite side. The piezoelectric green sheets 41 and 42 are alternately laminated, and the input electrodes 43 and 44 have a laminated structure of electrodes facing each other. The input terminal electrodes 46 and 47 and the output terminal electrode 48 are formed on the side surface of the laminate.
The input terminal electrodes 46 and 47 are respectively connected to the input electrode 4
It is electrically connected to one of the sets 3 and 44. Accordingly, the output terminal electrode 48 is electrically connected to the output electrode 45.

FIG. 4 is an exploded view of the lower protective case 32. As shown in FIG. 4A is a plan view, FIG. 4B is a front view, and FIG. 4C is a bottom view. The lower protective case 32 will be described. The lower protective case includes six metal terminals 51, 5
2, 53, 54, 55 and 56 project from the side. FIG. 5 shows a perspective view of this metal terminal. The metal terminal is made of a phosphor bronze alloy for a spring, and has a structure capable of holding the piezoelectric transformer element with a spring property. The metal terminals 51 and 52 are conductive one-pieces, and the connection terminals 57 are exposed on the bottom surface. Also, metal terminals 53 and 54
Similarly, the connection terminal 58 is exposed on the bottom surface.
These metal terminals 51, 52, 53, 54 are electrically connected to the output terminal electrode 48 of the piezoelectric transformer element 31.

The metal terminal 55 is electrically connected to the connection terminal 59 on the bottom surface, and the metal terminal 56 is electrically connected to the connection terminal 60 on the bottom surface. The metal terminals 55 and 56 are electrically connected to the input terminal electrodes 46 and 47. The lower protective case 32 has a projection 61 for supporting the piezoelectric transformer element 31.

FIG. 6 shows a plan view (a) and a sectional view (b) of the upper protective case 33. This upper protective case 33
Has a built-in connection conductor 62 for conducting the output electrode of the piezoelectric transformer element 31. This connection conductor 62
Since it is a high-voltage line, it is embedded in an insulating resin of a thickness necessary for insulation. The connecting conductor 62 has four protruding ends 63 for conducting with the metal terminals 51, 42, 53, 54 of the lower protective case 32.
Further, a projection 64 is provided on the inner surface of the side wall. The projection 64 is fitted into the recess 65 of the lower protective case.

Then, the piezoelectric transformer element 31 is mounted on the lower protection case 32. At this time, the piezoelectric transformer element 31 is held by utilizing the spring property of the metal terminal.
Then, the upper protective case 33 is covered. The upper protective case 33 and the lower protective case 32
5 are integrated by fitting. When the upper protective case 33 and the lower protective case 32 are fitted together, the protruding end 63 of the connection conductor 62 of the upper protective case 33 is formed.
A metal terminal 51 for an output electrode of the lower protective case 32,
42, 53, and 54 are brought into contact with each other to conduct electricity. This allows
The output electrodes at both ends of the center drive type piezoelectric transformer element 31 are conducted.

According to the embodiment of the present invention, the connection of the output electrodes at both ends of the central drive type piezoelectric transformer element is enabled by the protective case, and the connection lines for the output electrodes at both ends of the piezoelectric transformer element are connected. There is no need to provide it on a mounting board. This increases the mounting density of the mounting board,
High-density mounting becomes possible. This is also effective for downsizing the device.

In the embodiment of the present invention, the connection terminals 57 and 58 connected to the output electrodes are provided on both sides of the lower surface of the lower protective case 32. This may be on one side only. In addition, when provided on both sides, a symmetrical structure can be used to eliminate directivity. Further, the piezoelectric transformer element and the lower protective case 32 are fixed only by the spring property of the metal terminal.
For this reason, fixing work such as soldering can be eliminated, and man-hours can be reduced.

[0022]

According to the present invention, the output electrodes at both ends of the central drive type piezoelectric transformer element can be connected by the protective case, so that a high voltage line for connecting the output electrodes of the mounting board can be eliminated, and Measures can be reduced, and high-density mounting is possible, which is effective for miniaturization of equipment.

[Brief description of the drawings]

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

FIG. 2 is a perspective view of a piezoelectric transformer element according to one embodiment of the present invention.

FIG. 3 is a plan view of a piezoelectric sheet according to an embodiment of the present invention.

FIG. 4 is a development view of a lower protective case according to one embodiment of the present invention.

FIG. 5 is a perspective view of a metal terminal of a lower protective case according to an embodiment of the present invention.

FIG. 6 is a plan view and a sectional view of an upper protective case according to an embodiment of the present invention.

FIG. 7 is a perspective view of a conventional Rosen-type piezoelectric transformer.

FIG. 8 is an explanatory diagram of a center drive type piezoelectric transformer element according to the present invention.

FIG. 9 is a perspective view of a conventional center drive type piezoelectric transformer element.

FIG. 10 is a plan view and a rear view of a conventional mounting board.

[Explanation of symbols]

 31 Central drive type piezoelectric transformer element 32 Lower protective case 33 Upper protective case 41, 42 Piezoelectric sheet 43, 44 Input electrode 45 Output electrode 46, 47 Input terminal electrode 48 Output terminal electrode 51, 52, 53, 54, 55, 56 Metal terminal 57, 58, 59, 60 Connection terminal 61 Projection piece 62 Connection conductor 63 Projection end

Claims (2)

[Claims] 1. A piezoelectric transformer comprising: a central drive type piezoelectric transformer element having an input electrode opposed to a central part and output electrodes at both ends; and a protective case holding the element and mounted on a mounting board. A piezoelectric transformer, wherein a connection conductor for conducting between output electrodes at both ends of the piezoelectric transformer element is provided in a case. 2. The piezoelectric transformer element comprises a laminate of piezoelectric sheets having an input electrode at a central portion and output electrodes at both ends, wherein the input electrodes are alternately connected to input terminal electrodes on side surfaces. The output electrode is connected to output terminal electrodes on both side surfaces, and the protective case has a metal terminal that is electrically connected to the input terminal electrode and the output terminal electrode and has a spring property.
2. The piezoelectric transformer element is electrically connected and held by a spring property of the metal terminal.
3. The piezoelectric transformer according to item 1.