JPH0951134A - Piezoelectric transformer - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain a piezoelectric transformer with a small change in resonance frequency, a small resonance impedance, and a high boost ratio. A piezoelectric transformer in which input electrodes 11 and 12 facing the front and back surfaces are formed on one end side in the longitudinal direction of a rectangular piezoelectric ceramic plate 10 and an output electrode 13 is formed on the other end surface in the longitudinal direction is a part of the input electrode. Then, the output is obtained from the output electrodes positioned 180 degrees different from the input electrodes. The input electrode portion is polarized in the thickness direction of the piezoelectric ceramic plate, and the other portions have different polarization directions.

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. 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 which can realize a relatively low impedance and a relatively high step-up ratio.
It also allows you to inject relatively high power into the input,
A piezoelectric transformer capable of obtaining a large output is provided. Further, the present invention provides a piezoelectric transformer whose change in resonance frequency is small with respect to change in impedance.

[0007]

According to the present invention, by stacking piezoelectric ceramic substrates on which input electrodes and output electrodes are arranged, inputting them to the input electrodes of the stacked parts, and obtaining outputs from both ends of the piezoelectric ceramic plate, To solve the problem of.

That is, in a piezoelectric transformer having a rectangular piezoelectric ceramic plate with input electrodes on the front and back surfaces on one end side in the longitudinal direction and output electrodes on the end surface on the opposite side in the longitudinal direction, two piezoelectric ceramic plates are provided respectively. It is characterized in that an input electrode and an output electrode are formed, a piezoelectric ceramic plate is laminated at a portion of the input electrode, and the output electrode is located on the opposite side to the input electrode.

Further, in a piezoelectric transformer in which an input electrode is provided on a front surface and a back surface on one end side in the longitudinal direction of a rectangular piezoelectric ceramic plate, and an output electrode is provided on an end surface on the opposite side in the longitudinal direction,
Characteristically, input electrodes and output electrodes are respectively formed on three or more piezoelectric ceramic plates, the piezoelectric ceramic plates are laminated at the input electrode portions, and the output electrodes are alternately located on the opposite side of the input electrodes. It is a thing.

[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 or more output electrodes formed on the end faces of a plurality of piezoelectric ceramic plates 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. Electrodes 11a and 11b are formed on the surfaces of the two rectangular piezoelectric ceramic plates 10a and 10b at one end side in the longitudinal direction, and electrodes 12a and 12b are formed on the back surfaces facing the electrodes. This electrode 1
The piezoelectric ceramic plate 10 in the portion where 1 and 12 face each other is polarized in the thickness direction. The piezoelectric ceramic plates on which the input electrodes 11 and 12 are formed are laminated so that the input electrodes 12a and 12b are in contact with each other, and are adhered by a conductive adhesive or the like.

Electrodes 13a and 13b are formed on the longitudinal end faces of the piezoelectric ceramic plate 10, 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 13a and 14b are arranged on opposite sides of the input electrodes 11 and 12, that is, in directions different from each other by 180 ° to serve as output electrodes, and an output is obtained by a voltage generated between these electrodes. Ie these two electrodes
A load is connected between 13a and 13b to drive.

On a surface of a piezoelectric ceramic plate having a length of 22 mm, a width of 4 mm and a thickness of 0.5 mm, a length of 11 mm is provided on one end side as shown in FIG.
The characteristics were measured on a sample having an input electrode having a width of 4 mm and a width of 4 mm. 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 change in the resonance frequency of the piezoelectric transformer according to the present invention when it was open and when it was short-circuited was about 1.5%. On the other hand, in the case of the conventional one, there is a 4 to 5% change between open and short circuit, and the frequency change is greatly reduced.

Regarding the step-up ratio, when the load is 100 kΩ, the conventional one is 10.0 times, and the one according to the present invention is
It was 17 times.

The resonance impedance of the conventional one is 800 Ω to 1500 Ω under a load of 100 kΩ to 1 MΩ, whereas the resonance impedance of the present invention is 180 Ω to 280 Ω.
And was greatly reduced. The reason why such a low impedance can be obtained is that the coupling coefficient of the symmetric vibration is large, but there are also two layers on the primary side and the capacitance can be increased by increasing the area. Increasing the width of the electrodes to increase the capacitance
Since the combined vibration of the full length and the width causes the degenerate vibration, the full length vibration is not completed unless the ratio of the total length to the width is about 4 or more. According to the present invention, the impedance can be lowered and the capacitance can be increased without widening the width.

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 becomes low, a larger amount of electric power can be injected, and the output voltage can be increased accordingly.

Further, since the change in frequency is small, the frequency can be tracked at about 4 to 5% to 1.5%, so that the circuit configuration can be simplified and the change in output due to the change in impedance can be made small. You can

FIG. 2 is a perspective view showing another embodiment of the present invention. In this example, four piezoelectric ceramic plates 20a, 20
It is laminated by using b, 20c and 20d. The number of piezoelectric ceramic plates to be laminated can be arbitrarily selected.

In the piezoelectric transformer according to the present invention, it is possible to use not only fundamental mode vibration but also secondary and tertiary vibrations depending on the overall length and the dimensional ratio of the input electrodes. Therefore, the support can be provided at two or three places, and a stable pointing structure can be obtained.

[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 4 to 5 of the conventional one.
The output voltage can be doubled and a high output voltage can be obtained.

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.

Further, since the structure in which there is a gap between the laminated piezoelectric ceramic plates is used, the cooling effect is high, and it is easy to prevent heat generation and characteristic deterioration.

[Brief description of drawings]

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

FIG. 2 is a perspective view showing another embodiment of the present invention.

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

[Explanation of symbols]

 10:20: Piezoelectric ceramic plate 11, 12: Input electrode 13: Output electrode

Claims (5)

[Claims] 1. A piezoelectric transformer having a rectangular piezoelectric ceramic plate having an input electrode on the front and rear surfaces on one end side in the longitudinal direction and an output electrode on the end surface on the opposite side in the longitudinal direction. A piezoelectric transformer, wherein an input electrode and an output electrode are formed, a piezoelectric ceramic plate is laminated at a portion of the input electrode, and the output electrode is located on the opposite side to the input electrode. 2. A piezoelectric transformer having a rectangular piezoelectric ceramic plate having an input electrode on the front and back surfaces on one end side in the longitudinal direction and an output electrode on the opposite end surface in the longitudinal direction, wherein three or more piezoelectric ceramic plates are provided. A piezoelectric transformer characterized in that an input electrode and an output electrode are respectively formed, a piezoelectric ceramic plate is laminated at a portion of the input electrode, and the output electrode is alternately located on the opposite side to the input electrode. 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 a rectangular piezoelectric ceramic plate having an input electrode on the front and back surfaces on one end side in the longitudinal direction and an output electrode on the opposite end surface in the longitudinal direction. Is polarized in the thickness direction,
A piezoelectric transformer in which an input electrode and an output electrode are formed on two piezoelectric ceramic plates respectively, and the piezoelectric ceramic plates are laminated at the input electrode portion, and the output electrodes are located on opposite sides of the input electrode. . 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.