JPH0983036A - Piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a piezoelectric transformer having low oscillation impedance and high transformation ratio. SOLUTION: Piezoelectric ceramic plates 15, 16, each provided with an input electrode, are bonded to the central part in the long side direction of a rectangular piezoelectric ceramic plate 10. Oscillation of the piezoelectric ceramic plate 15, 16 is converted by an output electrode 11 at the end face of piezoelectric ceramic plate 10 to produce an output voltage. The capacity and oscillation mode can be regulated by varying the length of piezoelectric ceramic plate 15, 16 and the capacity can be increased by decreasing the thickness.

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 lighting a cold cathode fluorescent tube or the like, and more particularly to a piezoelectric transformer using separate piezoelectric ceramic plates for a primary side and a secondary side. .

[0002]

2. Description of the Related Art In a circuit requiring a high driving voltage, such as a cold cathode fluorescent tube, a copying machine, an electrostatic eliminator, etc., a conventional winding transformer is used to boost the input voltage in the primary and secondary windings. You are getting the output. Recently, the use of a piezoelectric transformer in this booster circuit has been studied and is being put to practical use.

FIG. 3 is a perspective view showing an example of the piezoelectric transformer, which is a so-called Rosen type. An input electrode 31 is provided on the front and back surfaces on one end side of the piezoelectric ceramic plate 30, and an output electrode 33 is provided on the opposite end surface.

In this piezoelectric transformer, when the secondary side is used as a high impedance load close to an open circuit, the input / output voltage ratio (step-up ratio) can be made large. However, when the load impedance is about 100 kΩ, the boosting ratio can be obtained only from several times to ten times. When a fluorescent tube used as a backlight of a liquid crystal panel is turned on, a sufficient step-up ratio can be obtained at the start of lighting, but a sufficient step-up ratio cannot be obtained in a low impedance state after the start of discharge.

Further, there is a limit in reducing the resonance impedance of longitudinal vibration due to the structure of the drive electrode, and there are many problems in injecting electric power, such as inability to inject large electric power. Further, the load impedance causes a shift in the resonance frequency, which causes a change in the resonance frequency of 4 to 5% with respect to the change in impedance from the open circuit to the short circuit.

[0006]

SUMMARY OF THE INVENTION The present invention provides a piezoelectric transformer capable of obtaining a relatively high step-up ratio even in a state of relatively low impedance. Another object of the present invention is to provide a piezoelectric transformer in which the resonance impedance value can be made as small as possible and a relatively high power can be injected into the input to obtain a large output.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems by driving a secondary side piezoelectric ceramic plate for obtaining an output by using a separate primary side piezoelectric ceramic plate on which an input electrode is formed. It is a solution.

That is, in a piezoelectric transformer having an output electrode on the end face in the long side direction of a rectangular piezoelectric ceramic plate polarized in the long side direction, the width is the same at opposite positions on both sides of the center of the piezoelectric ceramic plate. It is characterized in that the piezoelectric ceramic plates having the input electrodes formed on both sides are bonded to each other.

Further, the length of the piezoelectric ceramic plate on the primary side is changed, and the thickness is reduced to change the vibration mode and increase the input capacitance.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A metal film output electrode is formed on both lengthwise end faces of a piezoelectric ceramic plate polarized in the lengthwise direction,
The piezoelectric ceramic plates on the input side are bonded to both sides of the central portion of the piezoelectric ceramic plate. Input electrodes are formed on the front and back surfaces of the piezoelectric ceramic plate on the input side. The input electrode is connected to a power source and is connected so that the two piezoelectric ceramic plates vibrate in phase. The vibration generated in the piezoelectric ceramic plate on the output side by this vibration is output by the output electrodes at both ends.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an exploded perspective view showing an embodiment of the present invention. The output electrodes 11 are formed on both end faces of the rectangular piezoelectric ceramic plate 10 in the long side direction. The piezoelectric ceramic plate 10 is polarized in the length direction, that is, the direction between the output electrodes 11.

A piezoelectric ceramic plate 1 having a shorter length than the piezoelectric ceramic plate 10 is provided on both sides of the central portion of the piezoelectric ceramic plate 10.
Glue 5 and 16. Input electrodes 16a, 16b and 17a, 17b are formed on both surfaces of the piezoelectric ceramic plates 15, 16.
The piezoelectric ceramic plates 15 and 16 are polarized in the thickness direction. The two piezoelectric ceramic plates 15 and 16 are piezoelectric ceramic plates.
It is adhered to the center of 10 at a position where the distances to both lengthwise end faces of the piezoelectric ceramic plate 10 are equal.

FIG. 2 is a front view showing the connection for driving the piezoelectric transformer according to the present invention, in which the input electrodes 17a and 18b are connected in phase and the input electrodes 17b and 18a are connected in phase. For this reason, the polarization directions of the piezoelectric ceramic plates 15 and 16 are in the thickness direction, but opposite to the piezoelectric ceramic plates on the secondary side. Due to such polarization and connection, the piezoelectric ceramic plates 15 and 16 vibrate in the same direction depending on the input voltage.

A piezoelectric ceramic plate having a length of 22 mm, a width of 4 mm, and a thickness of 0.5 mm is used as an output side to form an output electrode on the end face of the long side, and a length of 5.5 to 11 mm, a width of 4 mm, and a thickness on the surface of the central portion.
The characteristics were measured with a 0.2-0.5 mm piezoelectric ceramic plate on which electrodes were formed and adhered. For comparison, a conventional Rosen type piezoelectric transformer shown in FIG. 3 having the same size was also prepared and the same measurement was performed.

The length of the input side piezoelectric ceramic plate is 7.3 mm
When set to (1/3 of the length on the output side), strong excitation can be achieved near 240 kHz of the fundamental and third harmonics. When the thickness of the piezoelectric ceramic plate on the input side was 0.5 mm and the fundamental wave was excited, a boost ratio of 11 times was obtained when the secondary side was loaded with 100 kΩ, and the input impedance at that time was 240 kΩ. If the thickness of the piezoelectric ceramic plate on the input side is 0.2 mm, the boost ratio is 20 times and the input impedance is 130 kΩ.

The length of the piezoelectric ceramic plate on the input side is 11 mm (
When the length on the output side is set to 1/2), the end of the junction becomes a fulcrum and can be excited by the second harmonic. When the thickness of the piezoelectric ceramic plate on the input side was 0.5 mm, a 10 times boost ratio was obtained, and the input impedance at that time was 170 kΩ. When the thickness of the piezoelectric ceramic plate on the input side was 0.2 mm, the boost ratio was 16 times and the input impedance was 100 kΩ.

The length of the piezoelectric ceramic plate on the input side is 5.5 mm
When set to (1/4 of the length on the output side), the input capacitance decreases and the characteristics deteriorate, but the load effect of the driving piezoelectric substrate decreases, and the basic vibration of the length vibration on the secondary side approaches. Resonance characteristics with less spurious can be obtained.

In the Rosen type, when the width is widened to reduce the impedance, combined vibration with the entire length occurs and degenerate vibration occurs, so that the total length needs to be four times or more the width. Similarly to the type of the present invention, the input impedance can be lowered and the capacitance can be increased by the length and thickness of the piezoelectric ceramic plate on the input side.

From the above results, the piezoelectric transformer according to the present invention is suitable for use in lighting a fluorescent tube, etc., and has a relatively high boost voltage not only when the load impedance is high but also when the load impedance is low. The ratio is obtained. Further, since the resonance impedance becomes low, a larger amount of electric power can be injected, and the output voltage can be increased accordingly.

Since the input side and the output side of the piezoelectric transformer according to the present invention are formed independently of each other, the coupling becomes smaller than that of the integrated type and a frequency change of about 4 to 5% occurs, but it can be covered by other characteristic aspects. There is almost no problem in practical use.

[0022]

According to the present invention, since the resonance impedance of the piezoelectric transformer can be lowered, heat generation can be suppressed and the input power can be reduced to 2 to 5 of the conventional one.
The output voltage can be doubled and a high output voltage can be obtained.

Further, since it is possible to excite the second and third harmonics, it is possible to support at a plurality of points, so that reliable support can be achieved and the influence on vibration can be easily reduced.

Since a relatively large boosting ratio can be obtained not only in the region where the load impedance is high but also in the region where the load impedance is low, it is not necessary to use a winding transformer or the like as an auxiliary boosting circuit.

[Brief description of drawings]

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

FIG. 2 is a front view showing an embodiment of the present invention.

FIG. 3 is a perspective view showing a conventional piezoelectric transformer.

[Explanation of symbols]

 10, 15, 16: Piezoelectric ceramic plate 11: Output electrode 17, 18: Input electrode

Claims (5)

[Claims] 1. A piezoelectric transformer having an output electrode on an end face in the long side direction of a rectangular piezoelectric ceramic plate polarized in the long side direction, the width being the same at opposite positions on both sides of the center of the piezoelectric ceramic plate. 2. A piezoelectric transformer characterized in that a piezoelectric ceramic plate having input electrodes formed on both sides is bonded to each other. 2. The piezoelectric transformer according to claim 1, wherein the polarization direction of the piezoelectric ceramic plate on which the input electrode is formed is the thickness direction. 3. A transformer according to claim 1, wherein the polarization direction of the piezoelectric ceramic plate having the input electrodes is the thickness direction, and the piezoelectric ceramic plate is symmetrical with respect to the piezoelectric ceramic plate having the output electrodes. 4. The piezoelectric transformer according to claim 1, wherein the length of the piezoelectric ceramic plate on which the input electrode is formed is 1/4 to 1/2 of the length of the piezoelectric ceramic plate on which the output electrode is formed. 5. The piezoelectric transformer according to claim 1, wherein the thickness of the piezoelectric ceramic plate on which the input electrodes are formed is smaller than the thickness of the piezoelectric ceramic plate on which the input electrodes are formed.