JP3230316B2 - Manufacturing method of piezoelectric transformer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a piezoelectric transformer suitable for obtaining a high-voltage power supply used for a continuous ignition device or a high-voltage generator for a black-and-white television.

[0002]

2. Description of the Related Art A typical piezoelectric transformer conventionally used is a so-called Rosen type piezoelectric transformer as shown in FIG. The piezoelectric transformer comprises a rectangular plate-shaped piezoelectric ceramic, and the driving portion 11 of the polarized in the thickness direction (Yazuki p ₁₎ primary, which is polarized in the longitudinal direction (Yazuki p ₂₎ of the secondary side And a power generation unit 12. By applying an AC voltage E ₁ of the AC frequency of the resonance frequency of the piezoelectric transformer to one wavelength (or half wavelength) resonance of this structure, the primary side is a low impedance electrical energy is converted into ultrasonic energy, then high voltage E ₂ is generated in the secondary side is high impedance. As the piezoelectric ceramics used in the piezoelectric transformer, those having an average crystal grain size exceeding about 1 μm are generally used.

[0003] In this piezoelectric transformer, a pair of electrodes are provided on a primary side in a thickness direction on a piezoelectric ceramic substrate using the above-described piezoelectric ceramics, and an electrode is provided on an end surface in a length direction on a secondary side. In the direction, the secondary side is longer than the coercive electric field at a predetermined temperature in the length direction.
It is manufactured by applying a voltage (approximately 30 minutes at about kV / mm) and performing polarization until it is almost saturated.

[0004]

In the prior art, however, since a piezoelectric ceramic having a crystal grain size exceeding about 1 μm is used, a high boosting ratio cannot be obtained, and a desired output voltage can be obtained. Therefore, the input voltage must be increased. As a result, large-amplitude vibration is applied to the piezoelectric ceramic, and the piezoelectric ceramic itself generates heat. Further, even if the input voltage is increased, the output voltage is not increased, and there is a problem that the piezoelectric ceramic is destroyed. As described above, in the case of piezoelectric ceramics having a crystal grain size exceeding about 1 μm, although there is an improvement effect due to the composition and the like, the use thereof is basically limited in applications involving a large amplitude such as a piezoelectric transformer.

Accordingly, the present applicant has previously filed Japanese Patent Application No. 4-33.
No. 5679 discloses a piezoelectric transformer in which the average particle diameter of crystal grains of a piezoelectric ceramic material powder is 1 μm or less. A material suitable for large-amplitude operation, such as the ability to obtain a high-voltage power supply, such as a high-voltage power supply, which could not be obtained with the piezoelectric ceramics used in the above-mentioned conventional example, by using the piezoelectric ceramics having a crystal particle diameter of submicron. As excellent.

However, when a Rosen-type piezoelectric transformer is manufactured using this new material, the following problems occur. In order to increase the step-up ratio, it is necessary to increase the electromechanical coupling coefficients K ₃₁ and K ₃₃ between the power generation unit and the drive unit. Therefore, in the polarization process in the manufacture of the Rosen-type piezoelectric transformer, a voltage was applied so as to be 100% saturated. However, the efficiency of the piezoelectric transformer obtained in this way is very good, but due to its efficiency, it cannot be adapted to an increase in input voltage, and as a result, excessive stress is applied to the output section. Also, the input voltage lower than that of the conventional piezoelectric transformer leads to destruction.

The present invention has been made in order to solve these problems, and can provide a high step-up ratio having a large mechanical strength such as a bending strength and a tensile strength and a large allowable input and output voltage. Another object of the present invention is to provide a method of manufacturing a highly reliable piezoelectric transformer that generates less heat.

[0008]

In order to achieve the object of the present invention, a method of manufacturing a piezoelectric transformer according to the present invention is directed to a method of manufacturing a rectangular plate formed by sintering piezoelectric ceramic material powder. The method for manufacturing a piezoelectric transformer in which a driving unit and a power generation unit are formed by polarizing the body in one half area in the thickness direction and the other half area in the length direction, As the powder, the average particle diameter of the crystal particles is 1 μm or less, and the amount of polarization for forming the driving section and the power generation section is 30 to 90% of the saturated state. It is attached.

[0009]

In a piezoelectric ceramic having an average crystal grain diameter of 1 μm or less, since the space between crystal grains is narrow, voids are less likely to be generated therebetween. Such piezoelectric ceramics do not crack or the like even when stress is applied, and have high bending strength and tensile strength.

[0010] A piezoelectric transformer using this piezoelectric ceramic has an increased allowable input and increased mechanical strength. In a piezoelectric transformer using this piezoelectric ceramic, the polarization amount is 30.
When the polarization process is performed in the range of% to 90%, a large output voltage is obtained with an increase in the input voltage, and the amount of heat generated on the primary side is small. Further, as the polarization amount approaches 90%, the characteristics become remarkable.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a piezoelectric transformer according to an embodiment of the present invention will be described below. Piezoelectric ceramic material powder having an average diameter of crystal grains of 1 μm or less is sintered to form a rectangular plate-shaped sintered body, that is, a transformer element. This transformer element has the structure described above and shown in FIG.

The dimensions of the transformer element used in this embodiment correspond to l = 50 mm, w = 10 mm, t = 2 mm, and the resonance frequency f = 73 kHz. The polarization condition of this transformer element is about 30% to 90% with respect to the saturation voltage. Under these conditions, FIG.
As shown in FIG. 4A, the polarization process is performed in the thickness direction when forming the primary side, and in the length direction when forming the secondary side as shown in FIG. Such a polarization treatment is performed by reducing the amount of polarization by 30%, 50%, 80%, 90%.
FIG. 1 shows an input voltage-output voltage characteristic in the case where the measurement is performed in%. As a comparative example, when performed at 10%, and at 100%
FIG. 1 also shows the input voltage-output voltage characteristics in the case where the measurement is performed in%.

As is apparent from this figure, 30% to 90%
%, A large output voltage can be obtained with an increase in the input voltage. 50% in this range
The output voltages below tend to be lower than those at 80% and 90%, and the amount of heat generated on the primary side also tends to increase somewhat as shown in FIG. The polarization condition in the present invention is desirably 80 to 90%, in which case the amount of heat generated on the primary side can be kept very low.

The amount of polarization was confirmed by heating the transformer element to 400 ° C. or higher, that is, the Curie point or higher, to remove the polarization, and to obtain a sample having a shape and dimensions as shown in FIGS. Is cut out, an electrode is formed, and repolarization is further performed until a saturated state is reached. Next, the ratio to the electromechanical coupling coefficient of the sample before cutting out and removing polarization was defined as the amount of polarization.

Compared with the above-described embodiment of the present invention, as a comparative example, the output voltage does not increase at a saturation voltage of, for example, 10%, and remains at a level, so that a high boosting ratio cannot be obtained. Further, as shown in FIG. 2, when the amount of polarization is 30% or less, the amount of heat generated on the primary side increases, which causes a reduction in the reliability of the element.

Further, when a 100% polarization in a saturated state is performed, the transformer element is destroyed at an input voltage as low as about 10V.

[0017]

As described above, according to the method for manufacturing a piezoelectric transformer of the present invention, as the powder forming the sintered body, the powder having an average crystal grain diameter of 1 μm or less is used. Since the amount of polarization for forming the drive unit and the power generation unit is set to 30 to 90% of the saturation state, a piezoelectric element having high mechanical strength such as bending strength and tensile strength can be obtained. It is possible to manufacture a piezoelectric transformer having a large allowable input and a high step-up ratio having a large output voltage. In addition, because of low heat generation, a highly reliable piezoelectric transformer can be obtained, and miniaturization, improvement of noise immunity, and safety of quality due to non-combustibility are superior to those that cannot be obtained with a wound-type transformer. The effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an input voltage-output voltage characteristic of an embodiment of the present invention.

FIG. 2 is a diagram for explaining a polarization amount-heat generation characteristic of an example of the present invention.

FIG. 3 is a diagram illustrating the structure of a piezoelectric transformer.

FIG. 4 is a view for explaining a polarization step according to an embodiment of the present invention.

FIG. 5 is a view for explaining the structure of an electrode used for confirming the amount of polarization in an example of the present invention.

[Explanation of symbols]

 11 ··· Drive unit 12 ··· Power generation unit

Claims (1)

(57) [Claims] 1. A rectangular plate-shaped sintered body formed by sintering a material powder of a piezoelectric ceramic, wherein one half of one side of the sintered body is in a thickness direction and the other half of one side is in a length direction. In the method of manufacturing a piezoelectric transformer in which a driving unit and a power generation unit are formed by being polarized, a powder having an average diameter of crystal particles of 1 μm or less is used as the powder. And the amount of polarization for forming the power generation section is 3
A method for manufacturing a piezoelectric transformer, which is set to 0 to 90%.