JPH09307152A - Piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inject large power, restrain heat generation, and prevent influence of frequency change, by driving a device at a frequency in the region where a vibration mode in the length direction and a vibration mode in the width direction are coupled. SOLUTION: Input electrodes 11 are formed on both surfaces of one side of a rectangular piezoelectric ceramic plate 10, and an output electrode 12 is arranged on an end surface of the opposite side. The ratio of the length L and the width W of the piezoelectric ceramic plate 10 is set nearly equal to 2. When driving is performed at the region where a vibration mode in the length direction and a vibration mode in the width direction are coupled, a high voltage at the time of lighting start of a fluorescent lamp is obtained. A high voltage is also obtained when lighting is continued. Therefore, the input of a high voltage is enabled, and heat generation can be restrained. Hence effective driving is enabled without being affected by the change of resonance frequency.

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. In particular, the present invention relates to both a high step-up ratio at the start of lighting and a relatively low step-up ratio at the time of lighting continuous. It relates to the obtained piezoelectric transformer.

[0002]

2. Description of the Related Art In circuits requiring a high drive voltage, such as cold cathode fluorescent tubes, copying machines, and static eliminators, conventionally,
The input voltage is boosted by the primary and secondary windings using a winding transformer to obtain an output and is driven. Recently, the use of a piezoelectric transformer in this booster circuit has been studied and is being put to practical use.

FIG. 6 is a perspective view showing an example of the piezoelectric transformer, which is a so-called Rosen type. An input electrode 61 is provided on the front and back surfaces on one end side of the piezoelectric ceramic plate 60, and an output electrode 62 is provided on the opposite end surface.

In this piezoelectric transformer, when the secondary side (output side) is used as a high impedance load close to open, 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 lighting a fluorescent tube or the like used as a backlight of a liquid crystal panel, 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 load state after the start of discharge.

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

Since this piezoelectric transformer utilizes longitudinal vibration, the length is set to 5 times or more the width in order to make it possible to regard components other than those in the length direction as zero. With a size of 50 x 8 x 2 mm, which has been put into practical use as a general shape, only a step-up ratio of about 8 times has been obtained with a low impedance load. Means are taken. However, using a winding transformer together has been an obstacle to miniaturization of the inverter circuit.

[0007]

SUMMARY OF THE INVENTION The present invention provides a piezoelectric transformer capable of obtaining a high step-up ratio under a high impedance load and a step-up ratio at which a fluorescent tube can be continuously lit even under a low impedance load. is there. Also, the resonance impedance can be made as small as possible, relatively large power can be injected, and heat generation can be suppressed,
A piezoelectric transformer that is not affected by frequency changes.

[0008]

According to the present invention, the ratio of the width to the length is increased as compared with the prior art, and the driving is performed at the frequency in the region where the vibration mode in the length direction and the vibration mode in the width direction are combined. By doing so, the above problems are solved.

That is, in a piezoelectric transformer having an input electrode on the front and back surfaces of approximately one half of the rectangular piezoelectric ceramic plate in the longitudinal direction, and an output electrode on the opposite end surface,
It is characterized in that it is driven at a frequency in a region where a vibration mode in the length direction and a vibration mode in the width direction are combined.

More specifically, the input electrodes are provided on the front and back surfaces of approximately one half of the rectangular piezoelectric ceramic plate in the longitudinal direction.
In a piezoelectric transformer having an output electrode on the opposite end surface, the portion of the piezoelectric ceramic plate where the input electrode is formed is polarized in the thickness direction and the other portion is polarized in the length direction, and the vibration mode in the length direction is set. It is characterized in that it is driven at the resonance frequency of spread vibration in which the vibration modes in the width direction are combined.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG. 1, a piezoelectric transformer according to the present invention has an input electrode 11 formed on the front and back surfaces on one side of a rectangular piezoelectric ceramic plate 10 and an output electrode 12 on the opposite end surface. The provision is the same as the conventional one. However, the ratio of the length L to the width W of the piezoelectric ceramic plate 10 is different from the conventional one.
It is smaller than the above, and is around 2. This value is preferably 1.75 to 2.05.

[0012] With this, by driving in the region where the vibration mode in the length direction and the vibration mode in the width direction are combined, a high voltage at the start of lighting of the fluorescent tube can be obtained, and a high voltage can be obtained even during continuous lighting. It is the one that makes it possible to obtain.

[0013]

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

The present invention has been made in the process of trial manufacture and measurement for examining the length-width ratio of the piezoelectric ceramic plate of the piezoelectric transformer. Piezoelectric ceramic plate with dimensions of 50 x 13 x 2 mm 10
As a result of measuring the output voltage in the vibration mode under the load of MΩ and 100 kΩ, different output voltage was obtained at each frequency as shown in FIG. 2 under the load of 10 MΩ. The results shown in Fig. 3 were obtained when a 100 kΩ load was applied.

As shown in FIG. 3, it was found that there is a frequency region where an output voltage higher than the fundamental wavelength mode main resonance output can be obtained when a 100 kΩ load is applied. This frequency region is the resonance region that depends on the vibration of the width, and is the output voltage of the main resonance.
Output voltages of 269V to 323V higher than 77V were obtained.

From the above results, in the region where the wavelength (λ) mode of vibration in the length direction and the frequency of ½ wavelength (λ / 2) mode of vibration in the width direction are coupled, at the time of high impedance close to open It is assumed that the required high voltage (step-up ratio) can be obtained.

From the above results, electrodes were formed on a piezoelectric ceramic plate having a length of 22 mm and a thickness of 0.5 mm, and L / L shown in FIG.
A sample having a W of 1.68 to 2.37 was prepared and the output at an input voltage of 10 V was measured. The results for a load of 10 MΩ and a load of 100 kΩ are shown in Fig. 4.

As is clear from this result, L / W is
There is a region where the frequencies match and are coupled in the vicinity of 2.0. In this region, a high voltage (step-up ratio) is obtained at high impedance load close to open, and in other regions, a high voltage is not obtained. Impedance load is 100 kΩ
In this state, an output of 200 to 350 V was obtained at any size, and 300 to 350 V was obtained in the coupling region. A step-up ratio far higher than that of the conventional 7 × 11 times when using the longitudinal vibration mode of the rod was obtained.

It has been found that there are three types of resonance due to the coupling of the vibration mode in the length direction and the vibration mode in the width direction.
Among them, it was confirmed that the spreading vibration due to the coupling of the λ mode of the vibration in the length direction and the λ / 2 mode of the vibration in the width direction has the strongest coupling and a large output can be obtained.

From the above results, the impedance is high at the start of lighting (discharging) like a cold cathode fluorescent tube, and a high voltage for discharging is required, but 1/3 to 1/1 at low impedance after discharging. For applications in which the constant lighting voltage of 4 is sufficient, it is suitable to use this piezoelectric transformer that can obtain the required boosting ratio in any case.

The above-described piezoelectric transformer according to the present invention utilizes the strongest vibration on the high-order side of the fundamental vibration in the longitudinal direction among the various resonances that occur. Examining the dimensional ratio, as shown in Fig. 4, a high output voltage is obtained when L / W is 1.79 to 2.00, and when L / W is around 1.9, the influence of other vibrations on the resonance region is obtained. I knew that I wouldn't get any. Therefore, the highest output is obtained in this vicinity.

The fundamental frequency of the resonance length is 80.4 k.
Hz, the combined vibration frequency was 179.9 kHz. The output of each vibration mode is shown in FIG.

When the above L / W is 1.9 and the coupling vibration frequency is 179.9 kHz, the output voltage is 1,256 V (step-up ratio 125.6 times), 100 kΩ in an open state of 10 MΩ or more.
The output voltage was 317V (boost ratio 31.7 times). Therefore, it was confirmed that both the high boost ratio at the start of lighting and the relatively low boost ratio at the continuous lighting can be obtained by the piezoelectric transformer according to the present invention.

A conventional piezoelectric transformer requires an input voltage of 50 to 70 V to light and maintain the state of a cold cathode fluorescent lamp of 110 to 220 mm with a diameter of 3 mm, whereas the piezoelectric transformer according to the present invention requires 15 V. The degree was enough.

[0025]

According to the present invention, it is possible to obtain a high voltage output required for starting the lighting of the cold cathode fluorescent tube and a voltage output required for continuing the lighting with one piezoelectric transformer. Therefore, it is not necessary to use the winding transformer together, and the inverter circuit and the like can be downsized.

Further, since it can be driven in a state where the resonance impedance is small, it becomes possible to inject high power and suppress heat generation.

Further, there is an advantage that the driving can be efficiently performed without being affected by the fluctuation of the resonance frequency.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram of characteristics of a piezoelectric transformer.

FIG. 3 is an explanatory diagram of characteristics of a piezoelectric transformer.

FIG. 4 is an explanatory diagram of characteristics of the piezoelectric transformer according to the present invention.

FIG. 5 is an explanatory diagram of characteristics of the piezoelectric transformer according to the present invention.

FIG. 6 is a perspective view of a conventional piezoelectric transformer.

[Explanation of symbols] 10, 60: Piezoelectric ceramic plate 11, 61: Input electrode 12, 62: Output electrode

Claims (6)

[Claims] 1. A piezoelectric transformer comprising a rectangular piezoelectric ceramic plate having an input electrode on the front and back surfaces of substantially half of one side in the longitudinal direction, and an output electrode on the end surface on the opposite side, in a longitudinal vibration mode and a width direction. A piezoelectric transformer characterized in that it is driven at a frequency in a region where the vibration modes of are coupled. 2. A piezoelectric transformer having a rectangular piezoelectric ceramic plate having an input electrode on the front and back surfaces of substantially half of one side in the longitudinal direction and an output electrode on the opposite end surface thereof, wherein the input electrode of the piezoelectric ceramic plate is formed. A piezoelectric transformer characterized in that one part is polarized in the thickness direction and the other part is polarized in the length direction, and is driven at a frequency of a region where a vibration mode in the length direction and a vibration mode in the width direction are combined. 3. A piezoelectric transformer having a rectangular piezoelectric ceramic plate having an input electrode on the front and back surfaces of substantially half of one side in the longitudinal direction and an output electrode on the end surface on the opposite side, in a longitudinal vibration mode and a width direction. A piezoelectric transformer characterized in that it is driven at the resonance frequency of the spreading vibration in which the vibration modes of the above are combined. 4. A piezoelectric transformer having a rectangular piezoelectric ceramic plate having an input electrode on the front and back surfaces of substantially half of one side in the longitudinal direction, and an output electrode on the opposite end surface, wherein the input electrode of the piezoelectric ceramic plate is formed. A piezoelectric transformer characterized in that one part is polarized in the thickness direction and the other part is polarized in the length direction, and is driven at the frequency of spreading vibration in which the vibration mode in the length direction and the vibration mode in the width direction are combined. . 5. The driving method according to claim 1, claim 2, claim 3 or claim 4, which is driven at a frequency in a region where a mode of a fundamental wavelength in a length direction and a mode of a half wavelength in a width direction are combined. Piezoelectric transformer. 6. The length-width ratio of the piezoelectric ceramic plate is 1.75.
The piezoelectric transformer according to claim 1, claim 2, claim 3, or claim 4, which has a value of ˜2.05.