JPH0951133A - Piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a piezoelectric transformer having a small change in a resonance frequency, a small resonance impedance and a high step-up ratio. SOLUTION: Input electrodes 11, 12 are formed on the front and rear of the central part in the longitudinal direction of a piezoceramic plate 10 having a widened width of the central part in the longitudinal direction, while two output electrodes 13, 14 are formed on both ends in the longitudinal direction. The parts of the input electrodes are polarized in the width direction of the piezoceramic plate and the other parts are varied in the polarization direction.

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 and the like, and more particularly to an electrode structure arranged on a piezoelectric ceramic plate.

[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. 2 is a perspective view showing an example of the piezoelectric transformer, which is a so-called Rosen type. An input electrode 21 is provided on the front and back surfaces on one end side of the piezoelectric ceramic plate 20, and an output electrode 23 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. Further, the present invention provides a piezoelectric transformer capable of injecting a relatively high power to the input and obtaining a large output. Further, the present invention provides a piezoelectric transformer whose change in resonance frequency is small with respect to change in impedance.

[0007]

SUMMARY OF THE INVENTION The present invention improves the shape of the piezoelectric ceramic plate and the arrangement of the input and output electrodes formed, and also obtains outputs from both ends of the piezoelectric ceramic plate to solve the above problems. Is the solution.

That is, in a piezoelectric transformer having input electrodes on part of the front and back surfaces of the piezoelectric ceramic plate and output electrodes on part of the end faces, the width of the central portion of the piezoelectric ceramic plate in the longitudinal direction is the longitudinal direction. The input electrodes are wider than the width of the end faces, and the input electrodes are formed on the front surface and the back surface of the wide central portion of the piezoelectric ceramic plate, and the output electrodes are formed on both end surfaces in the longitudinal direction.

Alternatively, in a piezoelectric transformer having an input electrode on a part of the front surface and the back surface of the piezoelectric ceramic plate and an output electrode on a part of the end surface, the width of the central portion of the piezoelectric ceramic plate in the longitudinal direction is Wider than the width of the end face and polarized in the thickness direction of the piezoelectric ceramic plate, the input electrodes are formed on the front and back surfaces of the wide central portion of the piezoelectric ceramic plate, and the output electrodes are formed on both end faces in the longitudinal direction. It is characterized by that.

[0010]

[Function] The input voltage is converted into mechanical vibration by the input electrodes arranged so as to face the front and back surfaces of the central portion of the piezoelectric ceramic plate,
A voltage generated between two output electrodes formed on both ends of the piezoelectric ceramic plate is used as an output voltage, and a load is connected between them.

[0011]

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

FIG. 1 is a perspective view showing an embodiment of the present invention. The width of the central portion of the piezoelectric ceramic plate 10 in the longitudinal direction is formed wider than the width of the end face in that direction, the electrode 11 is formed on the surface of this central portion, and the electrode 12 is formed on the back surface opposite to this. . The piezoelectric ceramic plate 10 in the portion where the electrodes 11 and 12 face each other is polarized in the thickness direction.

Electrodes 13 and 14 are formed on both end surfaces of the piezoelectric ceramic plate 10 in the longitudinal direction, respectively. The piezoelectric ceramic plate 10 in the portion where the input electrodes 11 and 12 are not formed is polarized in a direction other than the thickness direction. The two electrodes 13 and 14 become output electrodes, and an output is obtained by the voltage generated between these electrodes. That is, a load is connected between the two electrodes 13 and 14 for driving.

On the surface of a piezoelectric ceramic plate having a length of 22 mm, a width of the end face in the length direction of 4 mm, a width of the center portion of the length direction of 8 mm, and a thickness of 0.5 mm, the length of the center portion as shown in FIG. The characteristics were measured with a sample having an input electrode having a width of 11 mm and a width of 8 mm.
For comparison, the conventional Ro shown in FIG. 2 and having the same size is used.
A sen type piezoelectric transformer was also created and the same measurement was performed.

The resonance frequency of the piezoelectric transformer according to the present invention was 88.5 kHz when open and 87.3 kHz when short-circuited. On the other hand, in the conventional case, it was 82.9 kHz when open and 79.1 kHz when short circuited. This is 4-5 for the conventional one.
According to the present invention, the frequency change occurring in the range of
It is about 1.5%.

Regarding the step-up ratio, when the load is 10 kΩ,
The conventional one was 10.0 times at 79.2 kHz, while the one according to the present invention was 16.8 times at 87.3 kHz.

Regarding the resonance impedance, the conventional impedance is 800 Ω at 79.1 kHz at a load of 10 kΩ and 1500 Ω at 80.2 kHz at a load of 100 kΩ, whereas the conventional impedance is 10 kΩ. At 87.3 kHz at 150 Ω,
It was 230Ω at 87.8kHz with a load of 100kΩ.

From the above results, the piezoelectric transformer according to the present invention is suitable for use in, for example, lighting a fluorescent tube, and has a relatively high voltage boost 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 is lowered, it is possible to inject 4 to 5 times as much electric power as in the conventional piezoelectric transformer, and the output electric power can be increased accordingly.

Further, since the change of the frequency is small, the tracking to the frequency is good at about 4 to 5% to 1.5%, so that the circuit structure can be simplified and the fluctuation of the output due to the change of the impedance can be made small. You can

In the conventional Rosen type piezoelectric transformer, if the length of the piezoelectric ceramic plate is not more than four times the width, combined vibration of the entire length and width occurs and degenerate vibration occurs. In order to vibrate, it was necessary to exceed this length. With the structure according to the present invention, when the width of the central portion is increased, the length vibration is not affected even if it becomes 4 times or less, but 3 times or more is necessary due to manufacturing problems,
Below this, vibration is affected. Therefore, it is desirable that the width of the input electrode is in the range of 1 to 2 times the width of the output electrode.

[0021]

According to the present invention, since the resonance impedance of the piezoelectric transformer can be lowered, heat generation can be suppressed, and the input electric power is 2 to 2.
It is possible to increase the output voltage by 5 times and obtain a high output voltage.

Further, since the frequency change can be made small, the output fluctuation can be made small, and the circuit configuration for following the resonance frequency can be simplified.

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 perspective view showing a conventional piezoelectric transformer.

[Explanation of symbols]

 10: Piezoelectric ceramic plate 11, 12: Input electrode 13, 14: Output electrode

Claims (5)

[Claims] 1. A piezoelectric transformer having an input electrode on a part of a front surface and a back surface of a piezoelectric ceramic plate, and an output electrode on an end surface of a part of the piezoelectric ceramic plate. A piezoelectric transformer characterized in that the input electrodes are wider than the width of the end faces, and the input electrodes are formed on the front and back surfaces of the wide central portion of the piezoelectric ceramic plate, and the output electrodes are formed on both end faces in the longitudinal direction. 2. The piezoelectric transformer according to claim 1, wherein the input electrode and the output electrode are arranged symmetrically with respect to a center line in a direction orthogonal to the longitudinal direction. 3. The piezoelectric transformer according to claim 1, wherein a load is connected between the output electrodes on both end faces. 4. A piezoelectric transformer having an input electrode on a part of the front surface and the back surface of a piezoelectric ceramic plate and an output electrode on an end surface of a part of the piezoelectric ceramic plate. Wider than the width of the end face and polarized in the thickness direction of the piezoelectric ceramic plate, the input electrodes are formed on the front and back surfaces of the wide central portion of the piezoelectric ceramic plate, and the output electrodes are formed on both end faces in the longitudinal direction. Piezoelectric transformer characterized by 5. The piezoelectric transformer according to claim 4, wherein the piezoelectric ceramic plate in the portion where the input electrode is not formed is polarized in a direction different from that in the portion where the input electrode is formed.