JP2508575C - - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer operable with various power supply circuits for generating a high voltage, and in particular, to a small and thin piezoelectric transformer required to be small and highly reliable. And a piezoelectric transformer that generates a high voltage. 2. Description of the Related Art Conventionally, a winding type electromagnetic transformer has been used as a transformer for generating a high voltage in a power supply circuit in a device requiring a high voltage such as a deflection device of a television or a charging device of a copying machine. Have been. This electromagnetic transformer has a structure in which a conducting wire is wound around a core of a magnetic material, and it is necessary to increase the number of conducting wires to be wound in order to realize a high transformation ratio. Therefore, it has been very difficult to realize a small and thin electromagnetic transformer. On the other hand, a piezoelectric transformer using a piezoelectric effect has been proposed. FIG. 7 shows a structure of a Rosen type piezoelectric transformer which is a typical conventional piezoelectric transformer. Hereinafter, description will be given with reference to the drawings. When a high voltage is to be taken out, in the piezoelectric plate provided with electrodes on the surface, a portion indicated by 71 is a low impedance driving portion of the piezoelectric transformer, and electrodes 73 and 74 are provided on upper and lower surfaces thereof, and this portion is provided. It is polarized in the thickness direction as shown by the arrow in the figure. Similarly, a portion indicated by reference numeral 72 is a high-impedance power generation portion, and an electrode 75 is provided on an end face thereof. The power generation portion 72 is polarized in the length direction of the piezoelectric plate as indicated by an arrow in the drawing. . The operation of this piezoelectric transformer is as follows. When a voltage is applied to the drive electrodes 73 and 74 from the external terminals 76 and 77, an electric field is applied in the polarization direction in the drive unit 71, and the polarization is displaced in a direction perpendicular to the polarization (hereinafter, abbreviated as a piezoelectric transverse effect 31 mode). , Longitudinal vibration in the length direction is excited, and the entire transformer vibrates. Further, in the power generation section 72, a mechanical strain is generated in the polarization direction and a potential difference is generated in the polarization direction (hereinafter, abbreviated as a piezoelectric longitudinal effect 33 mode).
A voltage having the same frequency as the input voltage is extracted from the output electrode 75 to the external terminal 78.
At this time, if the drive frequency is made equal to the resonance frequency of the piezoelectric transformer, a very high output voltage can be obtained. When a high voltage is input and a low voltage is output, the high impedance portion 72 of the vertical effect is used as the input side, and the low impedance portion 71 of the horizontal effect is used.
It is clear that should be set on the output side. [0004] This piezoelectric transformer is used in a resonance state, and is (1) compared with a general electromagnetic transformer.
(2) The size and thickness can be reduced because the winding structure is unnecessary and the energy density is high.
And (3) there is no noise due to electromagnetic induction. [0005] In the conventional Rosen-type piezoelectric transformer, since the electrode of the power generation unit is located at the antinode of the vibration, the connection of the external terminal adversely affects the vibration or greatly reduces the reliability. There were disadvantages such as. In addition, a relatively high output voltage can be obtained when the load resistance is extremely large compared to the impedance of the piezoelectric transformer, but a very high output voltage cannot be obtained when the load resistance is not so large. Was. According to the present invention, in a piezoelectric ceramic transformer having a long plate structure, a plurality of piezoelectric ceramic layers and internal electrodes, each of which is polarized in the thickness direction of the entire length, are respectively laminated. Two drive units having a structure are arranged at both ends of the piezoelectric ceramic transformer, and a power generation unit polarized in the length direction is arranged at a center portion including the center in the length direction , and a portion that hits a node of vibration
A piezoelectric transducer and a driving method thereof, wherein a structure for taking out the Luo electrical terminals. The operation will be described below with reference to the drawings. FIG. 1A is a cross-sectional view of the piezoelectric ceramic transformer cut perpendicular to the width direction. FIG. 1B is a cross-sectional view taken along the line aa ′ in FIG. 1, and FIG. 1B is a cross-sectional view taken along the line bb ′, cc ′. Shown in c). This piezoelectric ceramic transformer has a structure in which the drive units 11 are arranged at both ends in the length direction, and the power generation unit 12 is arranged at the center. In the driving unit, the piezoelectric ceramic layers 111 polarized in the thickness direction are arranged so as to sandwich the internal electrodes 112 so that the polarization directions are alternately arranged.
13, 114 (115, 116). Here, the piezoelectric ceramic layer 1
Since 11 is an odd number of five layers, the external electrodes 113 are arranged on the upper and left sides and 114 are arranged on the lower and right sides in FIG. 1B, but when the number of piezoelectric ceramic layers 111 is even, either of them is used. The external electrodes are arranged on one side and two main surfaces, and the other external electrode is arranged only on the remaining one side. On the other hand, the piezoelectric ceramic 121 of the power generation unit is polarized in the longitudinal direction, and a relatively thin internal electrode 122 and an external electrode 124 on the surface are provided on both sides thereof. An electrode 125 is provided. At this time, the polarization direction is opposite to the internal electrode 123. The internal electrodes 122 and 123 are connected by external electrodes 124 and 125, respectively. The external electrode 124 is connected to the external electrodes 114 and 116 of the driving unit and functions as the same potential electrode, while an output terminal is taken out from the external electrode 125. The external electrodes 113 to 114 (115) of the driving unit 11 of the piezoelectric ceramic transformer
-116) when a voltage is applied between the piezoelectric transverse effect 3 via the electromechanical coupling factor k ₃₁
Longitudinal vibration in the length direction is generated by one mode. The longitudinal vibration is transmitted to the output unit 12, a voltage is generated in the piezoelectric longitudinal effect 33 mode via the electromechanical coupling coefficient k _33, and the voltage is extracted from the external electrode 125. At this time, if the frequency of the applied voltage is equal to the resonance frequency of the longitudinal vibration of the piezoelectric ceramic transformer, a considerably high output voltage can be obtained. Next, a description will be given of a method of extracting an external terminal which is advantageous for the present piezoelectric ceramic transformer.
FIG. 2 shows the connection method of the external terminals and the displacement and stress distribution in the longitudinal direction of the third mode of the longitudinal longitudinal vibration mode. The input terminal 21 is connected to the external electrodes 115 and 113 of the drive unit at connection points 24 and 25, respectively. The input / output common terminal 22 is an external electrode 116,
114 and connection points 26 and 27. The output terminal 23 is connected to the external electrode 125 of the power generation unit at a connection point 28. [0011] The third mode of longitudinal vibration is a vibration mode in which 3/2 wavelength of longitudinal vibration is equal to the entire length of the piezoelectric ceramic transformer. As shown in the displacement distribution of FIG. A
, B, and C exist. Of these, the nodes A and C are located inside the quarter wavelength from both ends, and the node B is the center of the entire piezoelectric ceramic transformer. Here, when comparing the positions of the nodes and the connection points, the connection points 24 and 26 are set to the node A, the connection points 25 and 27 are set to the node C, and the connection point 2
8 can be placed in node B. As described above, in the piezoelectric ceramic transformer having the structure of the present invention, all electric terminals can be taken out from nodes of vibration, so that good vibration characteristics and high reliability can be realized. A lumped constant approximation equivalent circuit near the resonance frequency of the piezoelectric ceramic transformer is shown in FIG. 3 like other piezoelectric transformers. In FIG. 3, Cd ₁ and Cd ₂ are the input side, respectively.
Damping capacity of the output side, A _1, A ₂ is the force factor of the input and output, m, c, r _m is the equivalent mass of the length longitudinal vibration tertiary mode, equivalent compliance is equivalent mechanical resistance. The input and output force coefficients A ₁ and A ₂ of the piezoelectric ceramic transformer of the present invention are represented by the following equations. ## EQU1 ## ## EQU2 ## Here, w: width, t: total thickness, l ₂ : half length of the output portion, ε: dielectric constant,
s: elastic compliance, k: electromechanical coupling coefficient As is apparent from the equivalent circuit of FIG. 3, generally, the output voltage V _out of the piezoelectric transformer changes depending on the resistance value of the connected load. The value of V _out also increases. However, in applications of high voltage and high power, the resistance value of the load is not so high, and the output voltage _Vout tends to be considerably lower than several times lower than when the output terminal is released. On the other hand, in the piezoelectric ceramic transformer according to the present invention, since the driving unit is constituted by the n piezoelectric ceramic layers, the force coefficient A ₁ represented by the equation (1) increases in proportion to the number n of layers. Therefore, an output voltage that is about n times as large as that of a piezoelectric transformer having a structure not stacked can be obtained, and a sufficiently high voltage can be supplied even to a relatively low load resistance. Further, in the piezoelectric ceramic transformer of the present invention, the internal electrodes 122 and 123 are arranged in the power generation unit as shown in FIG. In this case, the lines of electric force in the power generation unit 12 have little distortion and are almost parallel to the length direction. Therefore, the polarization of the piezoelectric ceramic of the power generation unit is uniform in the length direction and the electromechanical coupling coefficient k
₃₃ can be raised to near the limit of the material. (Example 1) As an example of a piezoelectric ceramic transformer according to the present invention, a piezoelectric ceramic transformer having the structure shown in FIG. 1 was manufactured by a green sheet method. The piezoelectric ceramic material with a PZT (PbZrO ₃ -PbTiO ₃₎ based piezoelectric ceramic. The internal electrode is 1
12, 122 and 123 were formed by screen-printing a Pt paste on a green sheet of a piezoelectric material and firing it together with the piezoelectric material. Here, a PZT-based piezoelectric ceramic and Pt are used as the material of the piezoelectric ceramic and the internal electrode, but it goes without saying that other combinations can be used as long as the piezoelectric ceramic material having piezoelectricity and an electrode material that can be integrally fired therewith. . Each of the electrodes of the driving unit and the power generation unit has a structure of five piezoelectric ceramic layers and four internal electrodes. The thickness of each piezoelectric ceramic layer was 0.2 mm, and the total thickness was 1 mm. After firing, the external electrodes 113, 114, 115, 116, and 124 are cut into dimensions of 30 mm in length and 5 mm in width, coated with an Ag paste, and fired.
, 125 and 126 were formed. These external electrodes may be formed by forming a thin film of a conductive material other than Ag using a method other than coating and firing, for example, a sputtering method as a vapor deposition method. After that, a polarization treatment of applying a voltage of 4 kV / mm in insulating oil at 100 ° C. was performed. Further, as shown in FIG. 2, the conductor was connected using solder. At this time, the connection points 24, 25, 26, and 27 of the drive unit were located 5 mm inside from both ends of the piezoelectric ceramic transformer. The resonance frequency of the third longitudinal mode in the longitudinal vibration of the piezoelectric ceramic transformer was measured to be 153 kHz from the frequency characteristics of admittance. When a 200 kΩ load resistance, which is relatively low resistance for high voltage use, is connected to this piezoelectric ceramic transformer, an output voltage of 650 V is obtained for an input voltage of 10 V, and the output power at this time is 2.1 W. Was. Further, 100 piezoelectric ceramic transformers according to this embodiment were driven continuously for 2000 hours, but none of the samples showed the peeling of the external electrode or the abnormality of the characteristics. The piezoelectric ceramic transformer can be used as a four-terminal transformer element as shown in FIG. That is, the output terminal 41 may be provided on the external electrodes 124 and 126 outside the power generation unit via the connection points 42 and 43. Although the connection points 42 and 43 are not nodes of the third mode of the longitudinal longitudinal vibration mode, the input terminal 21 and the
22 and the output terminals 23 and 41 are completely insulated from the direct current. Therefore, when used in a power supply circuit, the degree of freedom in circuit design increases. Embodiment 2 Subsequently, a piezoelectric ceramic transformer having no external electrodes on the upper and lower main surfaces was manufactured. The structure is shown in FIG. FIG. 5A is a cross-sectional view cut perpendicularly to the width direction, and FIG.
(C) is a sectional view taken along aa ′ and bb ′. In the driving section 51 of the piezoelectric ceramic transformer, inactive layers 513 of the piezoelectric ceramic are arranged above and below the three piezoelectric ceramic layers 511 and the four internal electrodes 512. The internal electrode 512 is shown in FIG.
As shown in the figure, external voltages 52 and 53 arranged on the side surface and external terminals 56 and 57 are connected. The location of this connection point is preferably located at the node of the vibration. On the other hand, in the power generation unit, the internal electrode 523 is connected to the output terminal 58 via the external electrodes 54 and 55 on the side as shown in FIG. In this case, the external terminal 55 is not always necessary. Similarly, the internal electrode 522 is connected by the external electrode on the side surface, and this external electrode is connected to one of the external electrodes 52 and 53 of the drive unit. The operating principle of this piezoelectric ceramic transformer is the same as that of the previous embodiment. Although the power that can be handled is reduced due to the decrease in the ratio of the active layer, the electrodes are not arranged on the upper and lower main surfaces, so that it is possible to support such that it is sandwiched by a conductor such as a metal from above and below at the node of vibration. When a load resistance of 200 kΩ was connected to the actually manufactured piezoelectric ceramic transformer, an output voltage of 510 V, that is, an output power of 1.3 W was obtained at an input voltage of 10 V. (Example 3) Further, a piezoelectric ceramic transformer having no internal electrode in the power generation unit was manufactured. FIG. 6 shows a sectional view perpendicular to the width direction. The driving unit 61 has exactly the same structure as that of the first embodiment, but the power generating unit includes a piezoelectric ceramic 621 polarized in the longitudinal direction and an external electrode 62.
2 only. The three external terminals are connected to external electrodes 613, 614, 622. When four external terminals are desired, external electrodes (corresponding to 124 in FIG. 1) may be provided relatively outside the power generation unit. In this embodiment, since there is no internal electrode in the power generation unit, even when a voltage is applied to the external electrode during the polarization process, the lines of electric force are not perfectly aligned in the length direction, which is somewhat disadvantageous in terms of efficiency. If the length of the power generation unit is sufficiently long compared to the thickness of the piezoelectric ceramic transformer, the decrease in efficiency is not so large. When a load resistor of 330 kΩ was connected to the piezoelectric ceramic transformer actually manufactured, the input voltage was 10 V
At this time, an output voltage of 680 V, that is, an output power of 1.4 W was obtained. As described above in detail, a piezoelectric ceramic transformer having a configuration according to the present invention has characteristics of high voltage, high power, high reliability, and is small and thin in the conventional art. The piezoelectric transformer has advantages that are not found in the piezoelectric transformer, and has great industrial value.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a piezoelectric ceramic transformer according to the present invention. FIG. 2 is a connection diagram and a displacement distribution diagram of the piezoelectric ceramic transformer of the present invention. FIG. 3 is a lumped constant equivalent circuit diagram of a piezoelectric ceramic transformer. FIG. 4 is a connection diagram of a piezoelectric transformer having a four-terminal structure. FIG. 5 is a sectional view of an embodiment having no electrodes on upper and lower surfaces. FIG. 6 is a cross-sectional view of an embodiment in which an internal electrode is not provided in a power generation unit. FIG. 7 is a perspective view of a conventional Rosen-type piezoelectric transformer. [Description of Signs] 11, 41, 51, 61, 71 Driving unit 12, 42, 52, 62, 72 Power generating units 111, 121, 511, 513, 611, 621 Piezoelectric ceramics 112, 122, 123, 512, 522, 523, 612 Internal electrodes 113, 114, 115, 116, 124, 125, 126, 52, 53, 54, 55, 613, 614, 622, 73, 74, 75, external electrodes 21, 22, 23, 41, 56. , 57, 58, 76, 77, 78 Electrical terminals

Claims (1)

Claims: 1. A piezoelectric ceramic transformer having a long plate structure, wherein a driving unit in which a plurality of piezoelectric ceramic layers polarized in a thickness direction and internal electrodes are alternately laminated is provided at both ends of the piezoelectric ceramic transformer. It is characterized by a structure in which a power generation unit polarized in the direction from the end to the center in the length direction is arranged in the center part including the center in the length direction , and the electric terminal is taken out from the part corresponding to the node of vibration. Piezoelectric ceramic transformer. 2. The piezoelectric ceramic transformer according to claim 1, wherein a single layer or a plurality of internal electrodes are arranged at a central portion in a longitudinal direction of the piezoelectric ceramic transformer, and output electric terminals are connected to all of the internal electrodes. Characterized in that a single layer or a plurality of internal electrodes are arranged at both ends of the piezoelectric element and connected to one electrode of a driving section. 3. The piezoelectric ceramic transformer according to claim 1, wherein a connection point between the external electrode of the drive unit and the conductive wire is set to a quarter of the wavelength of the longitudinal longitudinal vibration third mode from both ends of the piezoelectric ceramic transformer. A method for driving a piezoelectric ceramic transformer, wherein the piezoelectric ceramic transformer is disposed on the inner side and the piezoelectric ceramic transformer is driven at a resonance frequency of a third mode of longitudinal longitudinal vibration.