JPH1084142A - Piezo-electric transformer and drive method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezo-electric transformer which can be safely used and easily used, by eliminating any restrictions of its transformation ratio to improve its reliability and stability. SOLUTION: Combinations of means which follow are executed. (1) Means for providing driving parts 5 at both ends of a mechanical vibration node. (2) Means for setting polarization directions of both driving parts 5 in the same direction. (3) Means for providing an in-phase input to both driving parts 5. (4) Means for providing an electricity generating part 6 in the center of the mechanical vibration including the node. (5) Means for utilizing high-order vibration modes. (6) Means for setting the polarization directions so that generated voltages are added together. (7) Means for providing electrical terminals at which function also as support members at vibration nodes of the driving and generating parts 5 and 6.

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 various high-voltage power supplies, and more particularly to a small-sized and high-voltage power supply that requires high reliability and small size.

[0002]

2. Description of the Related Art Hitherto, a transformer for generating a high voltage used in a copying machine or a liquid crystal backlight has been an electromagnetic winding transformer in most cases.

On the other hand, a piezoelectric transformer having a completely different operating principle from that of a winding transformer has been known. FIG. 4 shows a typical structure example of this piezoelectric transformer. In FIG. 4, 1
Denotes a piezoelectric body, and electrodes 2 and 3 are formed on the upper and lower surfaces of the piezoelectric body. Further, the piezoelectric body of the drive unit performs polarization processing in the thickness direction, and the power generation unit performs polarization processing in the length direction. An input AC voltage is applied between the two electrodes 4. The portion 5 to which the input voltage is applied is called a driving unit.

On the other hand, the part 6 other than the driving part is called a power generation part. An electrode 7 is formed on the end face of the power generation section. An output is obtained from between the electrode 7 and the electrode 8. As a method of fixing the piezoelectric transformer, the support 9 is attached to a node at the time of resonance of longitudinal vibration in the longitudinal direction, and is supported and fixed.

In this state, when an AC voltage having a resonance frequency of the longitudinal vibration of the piezoelectric body 1 in the longitudinal direction is applied to 4, the piezoelectric body undergoes mechanical resonance. As a result, a high voltage having the same frequency as the input voltage is output from the power generation unit.

[0006]

The piezoelectric transformer shown in FIG. 4 is very attractive for an inverter for a backlight of a liquid crystal, which is required to be downsized. However,
There were the following major problems. (1) In the piezoelectric transformer shown in FIG. 4, the drive section and the power generation section are not connected to each other by the electrodes, and thus the reliability is significantly reduced. (2) The input voltage needs to be relatively high, and the degree of freedom in selection is small. (3) With regard to the output voltage, the degree of freedom in selecting the conversion ratio is small. (4) There were few terminals and support points, and there was concern about vibration and impact in use.

It is an object of the present invention to solve the above problems.

[0008]

According to the present invention, in order to solve the above-mentioned problems, (1) drive units are provided at both end portions including nodes of mechanical vibration. (2) Change the polarization direction of the drive unit. (3) In-phase inputs are given to both drive units. (4) A power generation unit is provided at a central portion including a node of mechanical vibration. (5) Use higher-order vibration modes. (6) The direction of polarization is set so that the generated voltage is added. (7) An electric terminal also serving as a support is provided at a node of vibration of the drive unit and the power generation unit. The above-mentioned problems can be solved for the first time by skillfully combining the various means described above.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of a piezoelectric transformer of a triple mode of λ / 2. In FIG. 1, 1 is a piezoelectric body, 2 and 3 are electrodes of a driving section, and an input voltage is applied between electrodes 4. Reference numerals 5 and 6 denote a drive unit and a power generation unit, respectively. Reference numeral 7 denotes a terminal / support provided in the power generation unit. An output 8 is obtained from the electrodes 3 and 7. Reference numerals 9 and 10 denote lower and upper electrode terminals respectively provided in the drive unit. In this figure,
Right and left arrows are shown on the front side. As shown by these arrows, the power generation unit is polarized in the same direction in the thickness direction, and the power generation unit is bisected at the center plane in the length direction and is polarized in the opposite directions.

Further, power supply noise generated when the piezoelectric transformer is driven by switching of the DC power supply was actually measured. That is, the piezoelectric transformer of this example was actually measured with the configuration of FIG.
In FIG. 3, 21 is a DC power supply, 22 is an electrolytic capacitor for smoothing, 23 is a choke coil, 24 is a varistor for power supply protection, 25 is an electronic switch, 26 is a piezoelectric transformer, and 27 is a load resistor.

The electronic switches were switched so that the repetition pulse frequency was at these resonance frequencies and the duty was 50%.

In FIG. 3, an electric field is applied to both ends of the drive units simultaneously in the same phase.

[0013]

EXAMPLE A piezoelectric transformer of a λ / 2 five times mode as shown in FIG. 2 was manufactured. The numbers shown in this figure are the same as those in FIG. In this figure, as indicated by an arrow on the front side surface, the drive section performed polarization processing in the same direction in the thickness direction. The power generation unit was divided into six regions at a distance of λ / 4 from the center plane, and was subjected to polarization processing so that the directions of polarization in regions adjacent to each other were opposite to each other in the length direction.

The length of the drive units 5 at both ends shown in FIG. 1 is λ / 2, the length of all the power generation units 6 is 1.5 λ, and the total length is 1.
The thickness was 21.2 mm, the width was 22.6 mm, and the thickness was 1.4 mm.

As a base plate for a piezoelectric transformer, NE is used as a piezoelectric material having a small electromechanical coupling coefficient k31 and a large k33.
A sintered body of PEC8 (trade name, manufactured by Tokin) was used. This sintered body was cut into a required shape to form a long plate.

As electrodes, 75% silver, 25 palladium
% Silver-palladium paste was patterned by conventional thick film screen printing and baked at 600 ° C.

As the polarization treatment, a DC electric field of about 1.5 KV / mm was applied in insulating oil heated to 150 ° C., and the resultant was held for 15 minutes.

The support of the driving unit was manufactured by punching a copper plate having a thickness of 0.1 mm. The length was the width of the electrode formed on the piezoelectric transformer plate. Its width was 0.3 mm.
This stamped copper plate was electrically welded to a lower surface corresponding to a node of vibration.

A support for the power generation section was formed by punching a hole slightly larger than a cross section of the piezoelectric transformer plate in the longitudinal direction on a copper plate having a thickness of 0.1 mm, and the punched copper plate was used as a support. A piezoelectric transformer element plate was inserted into the hole, and a support plate was fixed by electric welding to a silver-palladium electrode formed at a position corresponding to a longitudinal vibration node in the longitudinal direction.

Regarding the terminal attachment, a copper plate having a thickness of 0.1 mm was fixed to the center of a position corresponding to a vibration node on the upper surface of the drive section by punching spot welding into a 0.3 mm square.

An AC was input to the input section in the same phase, and the output terminal output both terminals 9 and 7 in parallel. At this time, the resonance frequency of the fifth mode is 64.4 kHz, and when the output impedance is 211 kΩ, the output 1300 is
V. That is, an output of 8 W was obtained.

As a reliability test of the piezoelectric transformer according to this embodiment, a continuous operation test was performed for 20,000 hours in an atmosphere having a relative humidity of 85% and a temperature of 80 ° C. As a result, none of the 150 test specimens had abnormal characteristics.

[0023]

According to the present invention, by using a higher-order vibration mode as required, the range of selection of the transformation ratio can be widened without changing the resonance frequency. That is, as described above, there is a great limitation on the voltage supplied from the main device. It is extremely effective when trying to overcome this limitation. Furthermore, when the input voltage is fixed, the output voltage can be increased according to the order of the vibration mode, which is also a very great advantage.

In addition, it is clear from the examples that the present invention provides an extremely reliable step-up transformer. It has been known that the conventional wound-type electromagnetic transformer always causes a short-circuit failure at high humidity and high temperature. However, according to the present invention, as is clear from the above-described embodiment, no fault such as a short-circuit fault has occurred. This is because the structure of the piezoelectric transformer of the present invention is simple and the structure is such that electrical connection can be performed only at required portions at nodes having the order of vibration.

The reason that conventionally known piezoelectric transformers are not widely used industrially is that the electrical connection is performed at an antinode of unstable mechanical vibration. Further, in the present invention, the fact that the support can be reliably provided at many nodes of mechanical vibration contributes to the improvement of stability. The present invention completely overcomes these difficulties.

[Brief description of the drawings]

FIG. 1 is a perspective view of a piezoelectric transformer according to the present invention in a λ / 2 triple mode.

FIG. 2 is a perspective view of a piezoelectric transformer according to the present invention in a λ / 2 five times mode.

FIG. 3 is a circuit configuration diagram showing one example of a method for evaluating and driving a piezoelectric transformer according to the present invention.

FIG. 4 is a perspective view showing a conventionally known piezoelectric transformer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric body 2 Electrode of drive part 3 Lower electrode of drive part 4 Input applied between 2 electrodes and 3 electrodes 5 Drive part 6 Power generation part 7 Terminal and support on power generation part electrode 8 Output between power generation electrodes 9 Drive electrode lower terminal 10 Drive electrode upper terminal 21 DC power supply 22 Electrolytic capacitor for smoothing 23 Choke coil 24 Varistor for power supply protection 25 Electronic switch 26 Piezoelectric transformer 27 Load resistance

Claims (5)

[Claims] 1. A piezoelectric transformer comprising a long-plate-shaped piezoelectric body and electrodes formed on the surface thereof, in a vibration mode three times as long as 1/2 of a wavelength λ of mechanical resonance of longitudinal vibration in a longitudinal direction of the piezoelectric body. The drive unit of the piezoelectric body is provided in both end regions including the node of mechanical resonance, the power generation unit is provided in the center region including the node of mechanical resonance, and the two regions at a distance of λ / 2 from both end surfaces of the piezoelectric body are the same in the thickness direction. A piezoelectric transformer, comprising: a driving unit polarized in a direction, wherein a polarization direction of a piezoelectric body in the power generation unit is a direction toward the two regions. 2. In a piezoelectric transformer comprising a long plate-shaped piezoelectric body and electrodes formed on the surface, an odd multiple of 5 or more of 1/2 of the wavelength λ of mechanical resonance of longitudinal vibration in the longitudinal direction of the piezoelectric body. In the mode, the drive unit of the piezoelectric body is provided in both end regions including the node of the mechanical resonance, the power generation unit is provided in the center region including the node of the mechanical resonance, and the two regions at a distance λ / 2 from both end surfaces of the piezoelectric body are thickened. A piezoelectric transformer having a drive section polarized in the same direction in the vertical direction. 3. The piezoelectric transformer according to claim 2, wherein a region excluding the driving portions at both ends of a distance λ / 2 from the end face is divided into λ / 4, and polarization in a region adjacent in the length direction of the piezoelectric body. A piezoelectric transformer having a power generation unit in which the directions of directions are different. 4. The piezoelectric transformer according to claim 1, wherein both the drive unit and the power generation unit are provided with a support member serving both as a support and an electric terminal at a node of mechanical resonance of longitudinal vibration in the longitudinal direction of the piezoelectric body. Characteristic piezoelectric transformer. 5. The piezoelectric transformer according to claim 1, wherein the back side of the long plate-shaped piezoelectric transformer is the same potential electrode of the drive section and the power generation section, the electrodes at both ends on the top side are the drive electrode, and the electrode of the center section. A driving method for a piezoelectric transformer, characterized in that the driving electrodes are used as electrodes of a power generation unit, and an in-phase driving voltage is applied to both driving electrodes.