JPH10125970A - Piezoelectric transformer - Google Patents

Abstract

(57) Abstract: Provided is a piezoelectric transformer capable of preventing abnormal oscillation of a tube current of a cold cathode tube, and thereby obtaining a stable output voltage. A substantially half portion on one side in the length direction of a piezoelectric plate is formed as an input portion, and a substantially half portion on the other side is formed as an output portion, and the output portion includes a power generation portion and a capacitance portion. Have been.
The input part A on which the input electrodes 2a and 2b are formed is polarized in the thickness direction, the output electrode 3 is formed on the end face in the length direction of the output part B, and the end of the output part B on which the output electrode 3 is formed. An electrode 6 for polarization is formed in the vicinity, the power generation section C constituting the input section A side of the output section B is polarized in the length direction, and the capacitance section D constituting the end of the output section B is not polarized. It is a non-polarized part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piezoelectric transformer used for an inverter for a backlight of a liquid crystal display, an inverter for lighting a fluorescent tube, and the like.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 5, for example, as shown in FIG. 5, a rectangular input electrode 2a, 2b
Are formed facing each other, the output electrode 3 is formed on the other end surface in the longitudinal direction, and the portion where the input electrodes 2a and 2b serving as the input portion A are formed is polarized in the thickness direction as indicated by an arrow P1. The other half of the output portion B is polarized in the length direction as indicated by an arrow P2.

This piezoelectric transformer utilizes a primary longitudinal vibration mode in the longitudinal direction, which is a so-called Rosen type piezoelectric transformer, and applies an input voltage between input electrodes 2a and 2b through input terminals 4a and 4b. The configuration is such that the boosted output voltage generated at the output electrode 3 is taken out through the output terminal 5 by the action of the piezoelectric effect and the inverse piezoelectric effect.

[0004] Such a piezoelectric transformer is used in a lighting circuit of a cold cathode tube for a backlight of a liquid crystal display, and the load characteristic of the output (boost ratio) is determined by the impedance before and after lighting (discharging) of the cold cathode tube and required characteristics. It has characteristics suitable for the applied voltage, and is used by directly connecting a cold cathode tube to the output terminal 5.

[0005] The brightness of the CCFL and the stabilization of the output are controlled by providing a feedback circuit from the output side to the input side, and controlling the output voltage (tube current) or the output voltage by converting it to a frequency. Have been done. That is, adjustment of the output voltage,
The control is performed by feeding back the output signal to the input side and changing the input voltage and the driving frequency of the piezoelectric transformer.

[0006]

However, in the conventional piezoelectric transformer, when the brightness of the cold-cathode tube is adjusted as described above, the phenomenon that the tube current of the cold-cathode tube oscillates as shown in FIG. Could happen. As described above, when the tube current is in an oscillating state, the output voltage becomes unstable, the control circuit does not operate normally, and there has been a problem that proper brightness adjustment cannot be performed.

Accordingly, an object of the present invention is to provide a piezoelectric transformer which can prevent abnormal oscillation of a tube current of a cold cathode tube and can obtain a stable output voltage.

[0008]

According to a first aspect of the present invention, there is provided a piezoelectric transformer comprising: a rectangular piezoelectric plate having input electrodes formed on both main surfaces and polarized in a thickness direction; And an output part which is provided adjacent to the input part in the length direction and partially has an output electrode is formed, wherein the output part is a power generation part which is polarized in the length direction and a power generation part which is polarized in the length direction. It is characterized by being constituted by a capacitance section which is not provided or polarized in a different polarization direction or a different polarization degree from the power generation section and functions as a capacitor.

According to a second aspect of the present invention, in the piezoelectric transformer according to the first aspect, the power generation unit and the capacitance unit are formed adjacent to each other in a length direction of the piezoelectric plate. It is.

According to a third aspect of the present invention, in the piezoelectric transformer according to the second aspect, the capacitance portion is formed adjacent to one of the input portion side and the input portion side of the power generation portion. It is characterized by having.

According to a fourth aspect of the present invention, in the piezoelectric transformer according to the second aspect, the power generation section is formed by being divided, and the capacitance section is formed between the power generation sections. It is.

According to the above configuration, the capacitance section functioning as a capacitor is formed at the output section of the piezoelectric transformer, and the capacitor is equivalently connected in series to the output section. Abnormal oscillation of the tube current of the cathode tube can be prevented. That is, by incorporating a capacitor in the output section of the piezoelectric transformer, the output impedance of the piezoelectric transformer can be changed (increased), and proper matching between the load output characteristics of the piezoelectric transformer and the load output characteristics between the cold cathodes is obtained. Therefore, even when adjusting and controlling the output voltage such as brightness adjustment, abnormal oscillation of the tube current does not occur, and a stable output voltage (tube current) can always be obtained.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the drawings showing embodiments thereof.

FIG. 1 shows the configuration of a piezoelectric transformer according to a first embodiment of the present invention.

The piezoelectric transformer of the present embodiment has a primary or secondary
FIG. 1 is a laminated piezoelectric transformer using a next longitudinal vibration mode, comprising a rectangular piezoelectric plate 1 formed by laminating a plurality of piezoelectric ceramic green sheets and integrally firing them.
As shown in FIG. 2, a substantially half part on one side in the length direction of the piezoelectric plate 1 is formed as an input part A, and a substantially half part on the other side is formed as an output part B. The output part B is composed of a power generation part C and a capacitance part D. It is configured.

The input portion A has input electrodes 2a and 2b opposed to each other, and the output portion B has an output electrode 3
Are formed, and a band-shaped polarization electrode 6 is formed in the width direction near the end where the output electrode 3 is formed.

The input section A is polarized in the thickness direction by applying a DC voltage between the input electrodes 2a and 2b as indicated by an arrow P1, and the power generation section C formed on the input section A side of the output section B is connected to the input electrode. A DC voltage is applied between the input electrodes 2a, 2b and the polarizing electrode 6 in a state where the electrodes 2a, 2b are short-circuited and polarized in the longitudinal direction as shown by an arrow P2, thereby forming an end of the output section B. The capacitance part D is a non-polarized part that is not polarized.

The power generation section C has a function of boosting the input voltage input to the input electrodes 2a and 2b, and the capacitance section D functions as a capacitor. The input portion A and the power generation portion C are formed with substantially the same dimensions, and the size of the capacitance portion D is set to an appropriate value in the range of several% to 30% of the power generation portion C according to the characteristics of the piezoelectric transformer and the cold cathode tube. Is done. For example, length 22mm, width 6m
m, a piezoelectric transformer having a resonance frequency of about 80 KHz with a thickness of 2 mm, the input section A is set to 10 mm, the power generation section C is set to 10 mm, and the capacitance section D is set to 2 mm.
H is selected.

The input electrodes 2a and 2b are alternately formed on the surface and inside of the piezoelectric plate 1, and the input electrodes 2a of each layer are connected at one end in the width direction, and the input electrode 2b of each layer is connected to the other end in the width direction. It is connected at the end face. In addition, the polarization electrode 6
Also, it is preferable to form the power generation section C in each layer in order to efficiently and uniformly polarize the power generation section C. When the polarization electrode 6 is formed in each layer, the polarization electrode 6 of each layer is connected at the end face in the width direction.

When the output voltage is adjusted or controlled, such as brightness adjustment, by using the piezoelectric transformer of this embodiment in a lighting circuit of a cold cathode tube, a stable tube current can always be obtained as shown in FIG. As a result, the occurrence of abnormal oscillation of the tube current as shown in FIG.

That is, in the piezoelectric transformer of this embodiment, a capacitor is connected in series to the output section B, so that the output impedance of the piezoelectric transformer is increased, the load output characteristics of the piezoelectric transformer and the cold cathode Thus, a stable output voltage (tube current) can be always obtained without causing abnormal oscillation of the tube current in a wide range of output voltage.

Next, the configuration of a piezoelectric transformer according to a second embodiment of the present invention is shown in FIG. In the piezoelectric transformer of the present embodiment, as shown in FIG. 3, a band-like polarization electrode 6 is formed near the input section A side of the output section B, and the polarization electrode 6 and the output section B in the longitudinal direction are formed. The space between the electrode and the output electrode 3 formed on the end face is polarized in the length direction as shown by an arrow P2,
Are formed, and a capacitance portion D of a non-polarized portion is formed between the input portion A and the polarization electrode 6.

That is, in the piezoelectric transformer of the present embodiment, the capacitance section D formed in the output section B is provided adjacent to the input section A. Other configurations are the same as those described in the first embodiment, and description thereof will be omitted.

In the configuration of this embodiment, the same operation and effect as those described in the first embodiment can be obtained.

Next, the configuration of a piezoelectric transformer according to a third embodiment of the present invention is shown in FIG. In the piezoelectric transformer according to the present embodiment, as shown in FIG. 4, two band-shaped polarization electrodes 6a and 6b are formed substantially at the center of the output portion B, and are provided between the input portion A and the polarization electrode 6a and for the polarization. The space between the electrode 6b and the output electrode 3 is polarized in the length direction to form two power generation units C, and
A non-polarized capacitance part D is formed between the two polarization electrodes 6a and 6b.

That is, in the piezoelectric transformer of the present embodiment, the capacitance section D is provided at the approximate center of the output section B, and the power generation section C is divided into two parts. Other configurations are the same as those described in the first embodiment, and description thereof will be omitted.

In the configuration of this embodiment, the same operation and effect as those described in the first embodiment can be obtained.

In each of the above embodiments, the polarization electrodes 6, 6a and 6b are used to polarize the power generation section C in the longitudinal direction, and may be deleted after the polarization.
The power generating unit C may be polarized by winding a metal conductor or the like without forming 6a and 6b.

In each of the above embodiments, the capacitance portion D has been described as a non-polarized portion that is not polarized. However, the polarization degree may be smaller than that of the power generation portion C, or the capacitance portion D may have a polarization direction different from that of the power generation portion C. Is also good.

Further, in each of the above embodiments, the laminated type piezoelectric transformer of the primary or secondary longitudinal vibration mode has been described as an example. However, the present invention is not limited to this, and the same configuration can be applied to a single-plate piezoelectric transformer. And 3
The present invention can be applied to a case where a longitudinal vibration mode of the next order or higher is used.

That is, the present invention is characterized in that a capacitance portion functioning as a capacitor is provided at the output portion of the piezoelectric transformer to prevent abnormal oscillation of the tube current of the cold cathode tube. There is no particular limitation.

[0032]

As described above, according to the piezoelectric transformer of the present invention, the capacitance section functioning as a capacitor is formed at the output section of the piezoelectric transformer, and the capacitor is equivalently connected in series to the output section. Thus, abnormal oscillation of the tube current of the cold cathode tube can be prevented in a wide range of output voltage. Therefore, even during the adjustment and control of the output voltage such as the brightness adjustment, the tube current does not cause abnormal oscillation, and a stable output voltage can always be obtained.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a tube current waveform when the piezoelectric transformer of the present embodiment is used in a lighting circuit of a cold cathode tube.

FIG. 3 is a perspective view of a piezoelectric transformer according to a second embodiment of the present invention.

FIG. 4 is a perspective view of a piezoelectric transformer according to a third embodiment of the present invention.

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

FIG. 6 is a diagram showing a tube current waveform when a conventional piezoelectric transformer is used for a lighting circuit of a cold cathode tube.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric plate 2a, 2b Input electrode 3 Output electrode 6, 6a, 6b Polarization electrode A Input part B Output part C Power generation part D Capacity part

(72) Inventor Yoshiaki Kono 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Prefecture Murata Manufacturing Co., Ltd. (72) Inventor Ken Takakura 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Murata Manufacturing Co., Ltd.

Claims (4)

[Claims] 1. A rectangular piezoelectric plate having input electrodes formed on both main surfaces and polarized in a thickness direction, and an output electrode provided in a portion adjacent to the input portion in a length direction and partially provided with an output electrode. The output unit is formed, wherein the output unit is a length-polarized power generation unit and a capacitor that is unpolarized or polarized in a different polarization direction or a different polarization degree from the power generation unit and functions as a capacitor. And a piezoelectric transformer. 2. The piezoelectric transformer according to claim 1, wherein the power generation unit and the capacitance unit are formed adjacent to each other in a length direction of the piezoelectric plate. 3. The piezoelectric transformer according to claim 2, wherein the capacitance section is formed adjacent to one of an input section side and an opposite side to the input section of the power generation section. 4. The piezoelectric transformer according to claim 2, wherein the power generation unit is formed in a divided manner, and the capacitance unit is formed between the power generation units.