JPH10270768A - Laminated type piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate such a failure as cracking by forming a plurality of hole parts near a boundary of an input electrode in a longitudinal direction of a laminated material of a central driving type laminated type piezoelectric transformer. SOLUTION: On a green sheet 51 of a piezoelectric porcelain, an inputting internal electrode 52 and a leader part 53 are formed by pattern-printing of a conductor, and a given number of green sheets are laminated, and they are contact-bonded and calcined, to obtain a laminated type piezoelectric transformer. In the inputting internal electrode 52, a plurality of holes 54 are formed near a boundary. The hole 54 is formed at pattern printing. A central driving type piezoelectric transformer in which an input electrode is disposed at the center of an element is formed, and further it is constituted in a laminated type. This drive system constitutes a 1/2 λ type piezoelectric transformer. Thereby such a failure as cracking is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated piezoelectric transformer used for voltage conversion.

[0002]

2. Description of the Related Art In recent years, power supply circuits such as a backlight inverter and a DC / DC converter for a liquid crystal display using a piezoelectric transformer have been actively studied.
The reason for this is that the adoption of the piezoelectric transformer makes it possible to realize a drastic reduction in size and thickness of the power supply circuit.

FIG. 5 shows an example of a piezoelectric transformer for this power supply circuit. This piezoelectric transformer is a conventional Rosen type piezoelectric transformer, for example, a lead zirconate titanate (PZ).
T), a pair of input electrodes 4, 6 provided by, for example, silver baking is formed on the upper and lower surfaces of the left half of the plate-shaped piezoelectric ceramic element 2 made of T), and the output electrodes 8 are formed on the right end surface in the same manner. Is formed. And the piezoelectric ceramic element 2
The left half of the drive unit is polarized in the thickness direction, and the right half of the power generation unit is polarized in the length direction as indicated by arrows.

In the piezoelectric transformer thus formed, when an AC voltage having substantially the same frequency as the longitudinal resonance frequency of the piezoelectric ceramic element 2 is applied between the input electrodes 4 and 6 from the AC voltage source 10, the piezoelectric ceramic The element 2 generates a strong mechanical vibration in the longitudinal direction, whereby electric charges are generated by the piezoelectric effect in the right half of the power generation unit, and an output voltage Vo is generated between the output electrode 8 and one of the input electrodes, for example, the input electrode 6. Occurs. The vibration mode of the piezoelectric ceramic element 2 is shown in FIG.
As shown in FIG. 6A, a half-wavelength mode (λ / 2 mode) that resonates at a half wavelength in the length direction and a one-wavelength mode (λ mode) that resonates at one wavelength as shown in FIG. is there.

When driven at the same frequency, the element of the piezoelectric transformer driven in the one-wavelength mode is twice as long as the element driven in the half-wave mode. For this reason, the piezoelectric transformer driven in the half-wave mode can be made smaller than the piezoelectric transformer driven in the one-wave mode. On the other hand, in terms of the boost ratio, the one-wavelength mode can obtain a higher boost ratio than the half-wave mode.

In addition to the single-plate type piezoelectric transformer shown in FIG. 5, a laminated type piezoelectric transformer has been proposed. FIG. 7 shows an example of this laminated type. This multilayer piezoelectric transformer element 1
In the figure, input electrodes 3 and 5 are formed in the front half of the figure, and an output electrode 7 is formed on the other end surface. This input electrode is also formed in the element 1 alternately with the piezoelectric ceramic material.
The input electrodes 3, 3a, 3b, 5, 5a, 5b are connected alternately. That is, the input electrodes 3, 3a, 3
b are connected by the connection electrodes 9 on the side surfaces, and the input electrodes 5, 5a,
5b is connected by the connection electrode 11 on the other side. And, by adopting this laminated type, a piezoelectric transformer having a higher step-up ratio can be configured as compared with the single-plate type structure.

As described above, in consideration of miniaturization, a stacked type piezoelectric transformer is more advantageous than a single plate type in order to drive in a half wavelength mode rather than a single wavelength mode and to obtain a high boosting ratio. It can be seen that it is.

[0008]

From the above, the present inventors have previously proposed a structure in which an input electrode is arranged at the center of a laminated piezoelectric transformer. In the present invention, various studies have been made on the structure of the input internal electrode of the central driving type laminated piezoelectric transformer.

First, FIG. 3 is a plan view showing the internal electrode structure of a comparative example. In this comparative example, the input internal electrodes 22 are alternately shifted to the center of the piezoelectric layer 21 so that one internal electrode faces one side surface. FIG. 4 shows the connection state of the internal electrodes after lamination of this comparative example.
The input internal electrodes 22 are alternately connected by connection electrodes 23 on the side surfaces.

When the input side electrodes of the laminated piezoelectric transformer are polarized, the piezoelectric layer extends in the polarization direction and contracts in a direction perpendicular to the polarization direction. For this reason, a tensile stress is generated near the boundary between the input internal electrode 22 and the power generation unit adjacent thereto.
In particular, in the central drive type, the portions that generate this stress are on both sides of the input internal electrode, and this is one of the causes of cracking of the piezoelectric transformer element during polarization or during driving after polarization.

SUMMARY OF THE INVENTION In view of the above, the present invention provides a laminated piezoelectric transformer that reduces tensile stress generated during polarization and does not crack during polarization and when driving the element.

[0012]

According to the present invention, a rectangular piezoelectric layer having an input electrode formed at a central portion is laminated, and a central portion having output electrodes formed at both longitudinal ends of the laminated body. A drive-type multilayer piezoelectric transformer, wherein a plurality of holes are formed near a boundary between the input electrodes in a longitudinal direction of the multilayer body.

[0013]

In the present invention, a plurality of holes are formed in the vicinity of the boundary between the input internal electrode 22 and the power generation section adjacent thereto, and the tensile stress generated at the boundary is reduced.

FIG. 1 is a perspective view of an embodiment according to the present invention. FIG. 2 is a plan view showing the state of the internal electrodes of this embodiment. In this embodiment, as shown in FIG. 2, an input internal electrode 52 is printed on a green sheet 51 of a piezoelectric ceramic by printing a pattern of a conductor (Ag / Pd paste or the like).
A predetermined number of the green sheets are laminated, pressed and fired to obtain a laminated piezoelectric transformer. The input internal electrode 52 of this embodiment has a plurality of holes 54 near the boundary. This hole 5
4 is formed at the time of pattern printing.

In this embodiment, as shown in FIG. 1, a pair of input electrodes 55 is formed on the upper and lower surfaces, and a connecting electrode 56 for connecting a lead portion 53 drawn to the side surface is formed on the side surface. Each is electrically connected to the upper and lower input electrodes 55. Output electrodes 57 are formed on both end surfaces of the laminated piezoelectric transformer 59. Lead wires 58 are soldered to the upper and lower input electrodes 55. At this time, the lead wire 58 is soldered at the center of the input electrode 55.

In this embodiment, a PZT-based piezoelectric ceramic material is used, and its outer diameter is 21.4 mm × 4.8 mm.
A laminated piezoelectric transformer having a size of × 1.6 mm (height) and 23 laminated layers was configured. Holes at the boundary of the input internal electrodes were arranged in two rows with holes having a diameter of 0.3 mm. 0.5 between holes in each row
mm, the distance between rows is 0.43 mm, and the total number of holes is 23 on one side.
And 46 on both sides. The polarization treatment was performed in silicone oil at 120 ° C., and between input and output was 2.5 kV / mm.
The electric field was applied for 5 minutes. Although fifty of these examples were prepared, no cracks occurred during polarization and during driving after polarization. In the structure of the comparative example, 3 out of 50 pieces
Individual cracks occurred.

This embodiment is a piezoelectric transformer of a center drive type in which an input electrode is arranged at the center of the element, and is constituted by a laminated type. This driving method constituted a 1 / 2λ type piezoelectric transformer. As a result, a piezoelectric transformer having a small size and a high step-up ratio without failures such as cracks could be formed.

In this embodiment, an input internal electrode is formed in the center of a rectangular piezoelectric layer, without being exposed to the side surface, inside, and is configured to face each other in the same region.
A lead portion sufficiently narrower than the internal electrode is formed.
Thereby, since the opposing internal electrodes have the same shape and are superimposed, it is possible to prevent the polarization in the horizontal direction except for a narrow region of the extraction portion. In addition, since the internal electrode is formed inside except for the lead-out portion, it is possible to prevent an electrical short circuit on the side surface due to atmospheric humidity (particularly migration of the Ag electrode) and contamination. Also, on the side,
Since only the electrode to be connected is exposed on the side surface, it can be easily connected and there is no danger of short circuit.

[0019]

According to the present invention, it is possible to configure a laminated piezoelectric transformer having a structure in which internal stress generated during polarization or driving is reduced, and problems such as cracks are prevented. A piezoelectric transformer having a ratio can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a plan view showing a state of an input internal electrode of the embodiment of FIG.

FIG. 3 is a plan view showing a state of an input internal electrode of a comparative example according to the present invention.

4 is a perspective view of the comparative example of FIG.

FIG. 5 is a perspective view of a conventional example.

FIG. 6 is a diagram showing a state of vibration in a half-wavelength mode and a one-wavelength mode.

FIG. 7 is a perspective view of a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 51 Green sheet of piezoelectric ceramic (piezoelectric layer) 52 Input internal electrode 53 Leader 54 Hole 55 Input electrode 56 Connecting electrode 57 Output electrode 58 Lead wire 59 Multilayer piezoelectric transformer

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Juichi Morikawa 70-2 Minamisakaemachi, Tottori City, Tottori Prefecture Inside the Tottori Plant of Hitachi Metals, Ltd.

Claims (1)

[Claims] 1. A central drive type laminated piezoelectric transformer in which rectangular piezoelectric layers each having an input electrode formed in the center are laminated, and output electrodes are formed at both ends in the longitudinal direction of the laminated body. A multilayer piezoelectric transformer, wherein a plurality of holes are formed near a boundary between the input electrodes in a longitudinal direction of the multilayer body.