JP2000332315A - Piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance reliability of a piezoelectric inverter by constituting the region of a piezoelectric transformer of a first region serving as an output part, a second region serving as an input part, and a third part serving as a rigid part which are set at a ratio of 4:4:2 in the longitudinal direction. SOLUTION: The piezoelectric transformer 5 resonating in primary mode in the longitudinal direction comprises a first region serving as an output part provided with an output electrode 6 on the end face, a second region serving as an input part provided with input electrodes 7, 8 on the upper and lower surfaces of a piezoelectric, and a third part serving as a rigid part provided with rigid part electrodes 9, 10 on the upper and lower surfaces of the piezoelectric. These regions are divided substantially at a ratio of 4:4:2 in the longitudinal direction. According to the arrangement, bending mode is suppressed and a longitudinal oscillation contributive to electric amount-mechanical amount conversion can be taken out efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device used as a lighting driving device such as a cold cathode discharge tube and a discharge lamp, and a vibrating body such as a piezoelectric vibrator, and a piezoelectric element or an electro-mechanical conversion element generally made of piezoelectric ceramic. More specifically, it is possible to convert an electric signal acting as a transformer such as a driving device used for a lighting driving device such as a cold cathode discharge tube and a discharge lamp and a driving device using piezoelectric ceramics into a mechanical displacement amount, The present invention also relates to a voltage boosting type piezoelectric transformer driving device capable of inverting a mechanical displacement into an electric signal.

[0002]

2. Description of the Related Art Recently, so-called laptop and palmtop type electronic devices such as small portable personal computers and word processors have rapidly become widespread. On the other hand, in these electronic devices, a liquid crystal display device is used as a display unit. It is well known that a circuit including a piezoelectric transformer is being considered for driving a cold-cathode discharge lamp used as a light source for illumination.

The above-mentioned piezoelectric transformer is capable of generating a high voltage by enlarging and outputting a mechanical displacement generated on a primary side on a secondary side. High voltage is obtained by converting it into a quantity and then into a quantity of electricity.However, since the driving load becomes a capacitive load, it has been difficult to output large power until now.
In order to obtain a practical output power, a higher-order mode having a higher order, such as a tertiary mode or a secondary mode, capable of obtaining a large output current has been used. (Reference: JP-A-8-2648
(See No. 54 Public Relations)

[0004]

However, in October 1997, an unprecedented thin mobile computer having a computer thickness of 18 mm was released in Japan. This has been a trigger, and mobile computers have become thinner and smaller.

[0005] Due to these facts, the liquid crystal display device has rapidly become thinner as a trend in the industry, and the distance between the cold cathode discharge tube used inside the backlight and the reflector (reflector) has been reduced to about 0.5 mm. Stray capacitance increases,
AC impedance value of conventional 150KΩ to 200
From KΩ, it was halved from 70 KΩ to about 100 KΩ.

[0006] The drive frequency of the wound-type backlight inverter, which has been widely used in the past, uses a frequency between 40 KHz and 60 KHz, and it is undeniable that the leakage current in the discharge tube portion is small and the shape is large. It had good use efficiency. In comparison with this, the backlight inverter frequency using a piezoelectric transformer, which is practically used due to its advantages of being light, thin, and small, is approximately 80 KHz.
高 い 120 KHz.

The main reason why the piezoelectric inverter uses a high frequency band is that, in order to obtain a large output current (5 mA to 6 mA), a one-wavelength mode of a secondary mode having two nodes of vibration, Alternatively, by using a 1.5-wavelength mode of the third mode in which three nodes of vibration are provided, the input impedance is reduced to several ohms to about 20 ohms, and two to three in the longitudinal direction of the piezoelectric transformer.
The formation of nodes at the vibrations suppresses the bending mode, enables efficient electrical-mechanical conversion by the intended longitudinal vibration, and achieves a practical output current of 5 mA.
From 6 mA to 6 mA.

The backlight inverter is becoming thinner and more compact, and has a length of, for example, 110 mm and a width between the computer body and a plurality of hinges to which a liquid crystal display unit housed in a lid (housing) is connected. What is stored in a small space of about 9 mm and thickness of about 4 mm is required.

Conventional piezoelectric transformers have used the one-wavelength mode of the secondary mode or the 1.5-wavelength mode of the tertiary mode. However, the tertiary mode has an excessively high frequency, so that a new liquid crystal display unit cannot be used. When the 50 kHz of a small leak current is realized by using the one-wavelength mode of the secondary mode due to a large leak current, a piezoelectric transformer having a length of about 70 mm is obtained, which has a disadvantage that circuit components cannot be mounted.

Next, in a Rosen type piezoelectric transformer which has been conventionally used, an input electrode is provided in a half dimension portion in a longitudinal direction, and an output portion is provided in another half dimension portion. In contrast, the polarization of the input portion is performed in the thickness direction, whereas the polarization of the output portion is performed in the length direction. I have.

When the piezoelectric transformer is driven by using the one-wavelength resonance mode of the secondary mode, two vibration nodes are formed at positions 22.4% from both ends with the total length being 100%. Since the inherent stress maximum portion and the stress maximum portion (nodes of two vibrations) generated during driving have different positional relationships, destruction due to stress concentration is unlikely to occur. In addition, there is no characteristic deterioration during long-time driving.

The piezoelectric transformer can be made lighter, thinner, shorter, and smaller by using a half-wave resonance mode of the first-order mode. And the maximum stress generated at the time of driving overlaps.
A crack is formed in the width direction substantially at the center of the piezoelectric transformer and breaks into two in the longitudinal direction.

Further, since the vibration node is located at one place in the center of the piezoelectric transformer, the amplitude of the bending mode increases when electric power is applied, and the excitation of the longitudinal vibration contributing to the conversion of electric quantity to mechanical quantity is reduced. , Output current upper limit is 3m
A. Attempts to extract an output current of 3 mA or more were accompanied by high heat generation, leading to destruction.

SUMMARY OF THE INVENTION The present invention aims at improving the disadvantages of the conventional piezoelectric transformer and obtaining a new, inexpensive, practical and highly reliable piezoelectric inverter. It is an object of the present invention to provide a piezoelectric transformer having various configurations and characteristics.

[0015]

In order to achieve the above object, a piezoelectric transformer according to the present invention focuses on a piezoelectric transformer that resonates at a half wavelength of a primary mode in a longitudinal direction of the piezoelectric transformer. The area of the piezoelectric transformer is composed of three areas of an output part serving as a first area, an input part serving as a second area, and a rigid body part serving as a third area, and is arranged in a longitudinal direction. It is composed of a ratio of approximately 4: 4: 2.

When an electric signal is applied to the input portion serving as the second region, the second region is polarized in the thickness direction, so that the second region is exposed to static internal stress in the width direction and the length direction. Excitation of resonance vibration in bending mode. The third region is polarized in a thickness direction different from that of the second region by 180 degrees, and the operation direction is oscillated in the opposite direction. Therefore, the third region acts mechanically as a rigid body, thereby suppressing the bending mode. Acts in the direction.

Thus, the center of the piezoelectric transformer in which the minimum position of the displacement is a half dimension of the piezoelectric transformer, the output section as the first area, and the input section as the second area,
The longitudinal vibration that occurs at almost the two starting points of the longitudinal vibration mode, which is located at the approximate center of the two regions, reduces the input impedance, suppresses the bending mode, and contributes to the electrical-mechanical conversion. For the first time, a novel configuration, effect, and characteristics of a piezoelectric transformer, in which the piezoelectric transformer is efficiently extracted, are realized.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on examples with reference to the drawings. FIG. 1 shows a Rosen type piezoelectric transformer that has been used conventionally. An output electrode 2 is provided on an end face of a rectangular piezoelectric ceramic 1.
And about 1/2 of the length direction of the piezoelectric transformer 1
An input electrode 3 and an input electrode 4 are provided on the upper and lower surfaces of the dimension portion, respectively.

After connecting a positive terminal (not shown) of a DC power supply to the input electrode 3 and connecting the input electrode 4 to a ground terminal (not shown), when a high DC voltage is applied between the two electrodes, an arrow is displayed. Polarization is performed in the thickness direction shown. Next, the input electrode 3 and the input electrode 4 are connected together to the ground terminal of the power supply, the positive electrode of the DC power supply is connected to the output electrode 2, and then a high DC voltage is applied between both electrodes. Polarization is performed in the direction.

FIG. 2 shows that the completed piezoelectric transformer 14 which has been subjected to polarization processing has a primary mode (モ ー ド wavelength) in the longitudinal direction.
The drive frequency that resonates with the piezoelectric transformer shows the state of vibration when the piezoelectric transformer is driven, and the curve shown by the dotted line shows the displacement distribution, in which the center of the piezoelectric transformer in the length direction is displaced. , And the displacement is maximum at both end faces. The curve shown by the solid line shows the stress distribution. The center of the piezoelectric transformer in the length direction is the maximum stress point, and the stress is minimum at both end faces.

As can be understood from FIG. 2, the maximum stress position generated during the polarization and the maximum stress generated by the drive are both superimposed on the center of the piezoelectric transformer.
When power is input to the piezoelectric transformer, the input power of about 2 W to 3 W causes a crack in the width direction substantially at the center of the piezoelectric transformer and breaks into two in the longitudinal direction.

In view of these characteristics, in the present invention, as shown in FIG. 3, in a piezoelectric transformer made of piezoelectric ceramics, a primary mode (1/1) is set in the longitudinal direction of the piezoelectric transformer.
A piezoelectric transformer 5 that resonates at two wavelengths) has an output portion serving as a first region provided with an output electrode 6 on an end face, and a second portion provided with input electrodes 7 and 8 on upper and lower surfaces of a piezoelectric ceramic. An input portion serving as a region, and a rigid portion serving as a third region in which rigid body electrodes 9 and rigid electrodes 10 are similarly provided on the upper and lower surfaces of the piezoelectric ceramic, wherein the first region is in a length direction indicated by an arrow. The second region is in the thickness direction indicated by the arrow, and the third region is in the second direction as indicated by the arrow.
The region is formed by applying polarization in the direction in which the phase of polarization in the thickness direction is opposite, and each of the regions is divided in the longitudinal direction at a ratio of approximately 4: 4: 2.

When an electric signal is applied to the input section serving as the second area via the input terminal 11 and the input terminal 12,
Since the second region is polarized in the thickness direction, the second region excites a static internal stress in the width direction and the length direction, and excites a bending mode resonance vibration. The third region has no electrical input means, and is polarized in a thickness direction different from that of the second region by 180 degrees, and the amount of electricity applied to the input portion of the second region is Since the mechanical amount after the electro-mechanical conversion propagates and excites vibrations whose operating directions are diametrically opposite each other, they mechanically act as a rigid body.
Region acts in a direction to suppress the bending mode.

From this, the center of the piezoelectric transformer where the minimum position of displacement is a half dimension of the piezoelectric transformer,
Of the output section serving as the area of the second area and the input section serving as the second area of the second area.
The input impedance is generated at two places substantially at the center of the two regions, substantially at the starting point of the longitudinal vibration mode, and the input impedance is increased from 70 Ω to 90 Ω in the related art to 10 Ω to 30 Ω in the present invention.
For the first time, a new configuration, effect, and characteristics of a piezoelectric transformer have been realized, in which the impedance is reduced to Ω, the bending mode is suppressed, and the longitudinal vibration that contributes to the electric quantity-mechanical quantity conversion is efficiently extracted from the output terminal 13. It was done.

As described above, in the piezoelectric transformer made of piezoelectric ceramics, the piezoelectric transformer that resonates in the primary mode (１ ／ wavelength) in the longitudinal direction of the piezoelectric transformer is driven near the center by the resonance frequency drive. This is the first realization of a piezoelectric transformer configured to have nodes that occur and a plurality of nodes that occur at the starting point of the longitudinal vibration.

As described above, in the piezoelectric transformer made of piezoelectric ceramics, the piezoelectric transformer that resonates in the primary mode (１ ／ wavelength) in the longitudinal direction of the piezoelectric transformer is located at the position of the maximum stress that is generated during the polarization and exists. This realizes a piezoelectric transformer configured for the first time so that the maximum stress position at the time of driving does not overlap.

Further, according to the structure of the present invention, the output impedance is arbitrarily designed between several tens KΩ and 300 KΩ by mainly changing the dimensions of the first region or adjusting the dimensions of the second and third regions. Since the output impedance of the piezoelectric transformer and the impedance of the actual load such as the cold cathode discharge tube can be matched at the design stage, it is possible to drive all lamps at low temperature or low brightness. Was.

Another embodiment according to the present invention is shown in FIG. In a piezoelectric transformer made of piezoelectric ceramics, a primary mode (1/2) is set in a longitudinal direction of the piezoelectric transformer.
(Wavelength), a piezoelectric transformer 5 'is provided with an output portion serving as a first region provided with an output electrode 6' on the end face, and input electrodes 7 'and 8' on the upper and lower surfaces of the piezoelectric ceramic. An input section serving as a second area, and a rigid body serving as a third area having no electrodes on the upper and lower surfaces of the piezoelectric ceramics, the first area extending in the length direction indicated by an arrow. The regions are formed in the thickness direction indicated by the arrows, and the third region is formed as an unpolarized region, and each of the regions is approximately 4:
It is divided and divided at a ratio of 4: 2.

An input terminal 1 is connected to the input section serving as the second area.
When an electric signal is applied through the input terminal 1 'and the input terminal 12', since the second region is polarized in the thickness direction, the internal stress in the width direction and the length direction is suppressed, and the resonance in the bending mode is prevented. Excite vibration. Since the third region has no electrodes and has no electric input means, and acts mechanically as a rigid body, the third region acts in a direction to suppress the bending mode.

From the above, the center of the piezoelectric transformer where the minimum position of the displacement is a half dimension of the piezoelectric transformer,
And an input section serving as a second area, which are located at substantially the center of the two areas, substantially at the starting point of the longitudinal vibration mode, and have an input impedance of 70 Ω in the related art. In the present invention, the impedance is reduced from 10 Ω to 90 Ω to 10 Ω to 30 Ω, the bending mode is suppressed, and the longitudinal vibration that contributes to the electric quantity-mechanical quantity conversion is efficiently extracted from the output terminal 13 ′. It has been realized for the first time that various configurations, effects and characteristics are realized.

[0031]

Since the present invention is configured as described above, it has the following effects.
A piezoelectric transformer that resonates at a half wavelength of the first mode in the longitudinal direction of the piezoelectric transformer is formed from an output section serving as a first area, an input section serving as a second area, and a rigid body serving as a third area. With this configuration, a piezoelectric transformer that has been conventionally practically used has a length, width, and weight that are almost half.

Further, since the maximum stress portion generated during polarization and the maximum stress position during driving do not overlap with each other, the conventional piezoelectric transformer broken at 2 W to 3 W is provided by the present invention. A small, thin, and lightweight piezoelectric transformer can be used with a large power of 6 W to 7 W.

The drive frequency, which has been used in the high frequency band between 80 KHz and 120 KHz, can be driven at a low frequency of 50 KHz, so that the leak current in the discharge tube section is reduced to about half. As a result, a highly efficient inverter was realized.

In the present invention, the input impedance is reduced to 70% of the conventional piezoelectric transformer by adopting a new concept of the piezoelectric transformer called the rigid portion in the third region.
By reducing the high impedance of Ω to 90 Ω to about 10 Ω to 30 Ω in the present invention, it is possible to use with high power.

Further, in the configuration of the present invention, the output impedance is arbitrarily designed between several tens of KΩ to about 300 KΩ mainly by dimensional change of the first region or dimensional adjustment of the second and third regions. Since the output impedance of the piezoelectric transformer and the impedance of the actual load such as the cold cathode discharge tube can be matched at the design stage, it is possible to drive all lamps at low temperature or low brightness. It has many effects on a practical level.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a conventional piezoelectric transformer.

FIG. 2 is a diagram showing a stress distribution and a displacement distribution of a conventional piezoelectric transformer.

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric ceramics 2, 6, 6 'Output electrode 3, 4, 7, 7', 8, 8 'Input electrode 5, 5' Piezoelectric transformer 9, 10 Rigid body electrode 11, 11 ', 12, 12' Input terminal 13 , 13 'Output terminal 14 Piezoelectric ceramic finished product

Claims (5)

[Claims] In a piezoelectric transformer made of piezoelectric ceramics, a piezoelectric transformer that resonates in a primary mode (１ ／ wavelength) in the longitudinal direction of the piezoelectric transformer includes: A piezoelectric transformer, wherein the maximum stress position is located without overlapping. 2. A piezoelectric transformer made of piezoelectric ceramics, wherein a piezoelectric transformer that resonates in a primary mode (波長 wavelength) in a longitudinal direction of the piezoelectric transformer has a node formed near a center portion by driving at a resonance frequency. A piezoelectric transformer having a plurality of nodes generated at the starting point of the longitudinal vibration. 3. An output section in which a piezoelectric transformer resonating in a primary mode (で wavelength) in a longitudinal direction of the piezoelectric transformer in a longitudinal direction of the piezoelectric transformer is a first area, and a second area is provided. A piezoelectric transformer, comprising: an input portion; and a rigid region serving as a third region, wherein the three regions are divided at a ratio of approximately 4: 4: 2 in the longitudinal direction. 4. In a piezoelectric transformer made of piezoelectric ceramics, a piezoelectric transformer that resonates in a primary mode (１ ／ wavelength) in a longitudinal direction of the piezoelectric transformer becomes a first region having an output electrode provided on an end face. An output unit, an input unit serving as a second region in which electrodes are provided on the upper and lower surfaces of the piezoelectric ceramic, and a rigid body serving as a third region in which electrodes are provided on the upper and lower surfaces of the piezoelectric ceramic. The first region is polarized in the length direction, the second region is polarized in the thickness direction, and the third region is polarized in the direction in which the polarization direction in the thickness direction is opposite to that of the second region. A piezoelectric transformer characterized by being divided in the longitudinal direction at a ratio of approximately 4: 4: 2. 5. In a piezoelectric transformer made of piezoelectric ceramics, a piezoelectric transformer that resonates in a primary mode (１ ／ wavelength) in a longitudinal direction of the piezoelectric transformer becomes a first region in which an output electrode is provided on an end face. An output unit, an input unit serving as a second region in which electrodes are provided on the upper and lower surfaces of the piezoelectric ceramic, and a third unit having no electrodes on the upper and lower surfaces of the piezoelectric ceramic.
Wherein the first region is polarized in the length direction, the second region is polarized in the thickness direction, and the third region is an unpolarized region. 3. The piezoelectric transformer according to claim 1, wherein the three regions are each divided at a ratio of approximately 4: 4: 2.