JP3353132B2 - 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 piezoelectric transformer using a piezoelectric vibrator, and more particularly to a piezoelectric transformer having interdigital electrodes inside a piezoelectric ceramic rectangular plate and utilizing resonance in a longitudinal direction of the rectangular plate. is there.

[0002]

2. Description of the Related Art With the spread of various portable electronic devices such as portable televisions and notebook personal computers, AC adapters that use a commercial AC voltage as a power source and output a DC voltage have been used to supply a DC voltage to these devices. I have. FIG. 3 shows a circuit diagram of a general AC adapter. On the input side, there is first a common mode choke coil for countermeasures against electromagnetic noise, then there is a full-wave rectifier circuit, and then there is a smoothing capacitor in parallel with the DC circuit for countermeasures against a large momentary disconnection. Next, there are switches S1 and S2 for converting DC to AC, and the converted AC voltage enters an electromagnetic transformer and is converted to a predetermined AC voltage. Finally, a switching type AC adapter rectifies the AC voltage and outputs a predetermined DC voltage. Among the electronic components used for the AC adapter, an electromagnetic transformer has a large volume and affects the conversion efficiency of the AC adapter. Recently, higher efficiency, smaller size and lower profile for AC adapter,
There is an increasing demand for reduction of electromagnetic noise and low power consumption, and instead of an electromagnetic transformer, a piezoelectric transformer using energy of mechanical vibration as a conversion medium is being studied. As a piezoelectric transformer, a Rosen type is generally used, but high efficiency cannot be obtained because the output side braking capacity is small. For the efficiency of the piezoelectric transformer, the impedance matching between the output impedance of the piezoelectric transformer and the load is important, but the input impedance of various portable electronic devices connected to the output part of the AC adapter is about several Ω to several Ω.

The output impedance of a piezoelectric transformer is determined from the angular frequency ω (= 2πf) and the output-side braking capacitance Cd2 as shown in equation (1).

R = 1 / ωCd2 (1) Here, as an example, when R = 10Ω and f = 120 kHz, Cd2 = 160 nF.

[0005] In a piezoelectric transformer for an AC adapter having practical dimensions, in order to secure such a large braking capacity, a laminated structure including opposed internal electrodes is required.

[0006]

However, in order to adopt an opposing internal electrode on the output side for impedance matching, the lamination direction of the internal electrode and the ceramic coincides with the length direction of the piezoelectric ceramic rectangular plate ( k33) and the method (k31) that matches the thickness direction.

The former can expect a higher electromechanical coupling coefficient than the latter, so that the energy conversion efficiency of the piezoelectric transformer is increased. However, since the lamination direction coincides with the length direction of the piezoelectric ceramic rectangular plate, a problem remains in terms of mechanical strength.

That is, the noble metal, which is the internal electrode layer, and the piezoelectric ceramic do not chemically react with each other, and are merely mechanically fixed. When driven at the resonance frequency in the length direction, there is a possibility of breaking from the boundary surface between the internal electrode and the ceramic. Furthermore, the lamination in the length direction has a large number of laminations and is problematic in terms of cost. On the other hand, in the latter case in which the layers are stacked in the thickness direction, since k31 is used, there arises a problem that the energy conversion efficiency is reduced as compared with the case where k33 is used, and the volume may be increased.

Therefore, an object of the present invention is to make the internal electrodes not the plane electrodes but the interdigital electrodes and to make the lamination direction the thickness direction of the piezoelectric transformer rectangular plate, so that the mechanical strength is high, the energy conversion efficiency is good, and An object of the present invention is to provide a low cost piezoelectric transformer.

[0010]

SUMMARY OF THE INVENTION In a piezoelectric transformer utilizing a longitudinal resonance mode of a piezoelectric ceramic rectangular plate, a set of intersections parallel to the longitudinal direction is provided at substantially half of the rectangular plate in the longitudinal direction. A finger internal electrode group and a lead electrode exposed on the side surface of the rectangular plate from the cross finger internal electrode, and a substantially half portion in the length direction of the rectangular plate has a set of crosses parallel to the length direction. A finger internal electrode group and a lead electrode exposed on the side surface of the rectangular plate from the cross finger internal electrode, a plurality of the cross finger electrodes and the lead electrode are arranged in the thickness direction, and the lead electrodes are respectively provided on the side surfaces of the rectangular plate. A piezoelectric transformer characterized by a structure connected to an external electrode is obtained.

Further, in a piezoelectric transformer using a resonance mode in the length direction of the piezoelectric ceramic rectangular plate, a set of inter-finger internal electrode groups parallel to the length direction is provided on almost half of the length of the rectangular plate in the length direction. The other half of the rectangular plate in the longitudinal direction is composed of a set of interdigitated internal electrodes parallel to the longitudinal direction. The piezoelectric transformer is characterized in that it is connected to the external electrodes at approximately one-fourth positions and the interdigital electrodes are arranged in a plurality in the thickness direction.

[0012]

In the present invention, the vibration direction of the vibrator is the length direction, and the repetition direction of the interdigital electrodes is the width direction of the rectangular plate.
As the piezoelectric transformer, both the input and the output utilize the piezoelectric lateral effect. In the case of surface interdigital electrodes, it is generally known that, depending on the dimensions of the electrode width and the distance between the electrodes, there is a dimensional relationship in which the piezoelectric lateral effect is more efficient than the piezoelectric longitudinal effect. Therefore, also in the internal interdigital electrode structure of the present invention,
We have found that the same effect can be obtained, and even if it is miniaturized, it does not reach the vibration level limit inherent to the material,
It is possible to provide a piezoelectric transformer having a low vibration speed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A piezoelectric transformer according to first and second embodiments of the present invention will be described in the following first and second embodiments with reference to the drawings.

Embodiment 1 FIG. 1 schematically shows a structure of a piezoelectric transformer according to the present invention. After forming a high-Qm piezoelectric ceramic green sheet, the pattern shown in FIG. 2, that is, a plurality of interdigital internal electrodes (a set of interdigital internal electrode groups parallel to the length direction) 12 was printed on the sheet. . Next, after laminating the required number of sheets and hot pressing, the sheets were cut into predetermined dimensions and debindered. Further, sintering is performed at 1100 ° C. for 2 hours, and after sintering, input-side external electrodes 13 a and 13 b and output-side external electrodes 14 a and 14 b are formed on the piezoelectric ceramic rectangular plate 11.

More specifically, the lead-out electrodes 12-1, 12-2, 12-3, 12 extending from the exposed interdigital electrodes 12 on the side surfaces of the piezoelectric ceramic rectangular plate 11 are exposed.
-4, input-side external electrodes 13a and 13b and output-side external electrodes 14a and 14b were formed to produce a piezoelectric transformer element.

The device fabricated as above was heated at 150 ° C.
Electric field strength 1kV / mm for both input and output in silicone oil
For 15 minutes to obtain a piezoelectric transformer vibrator.

[Embodiment 2] FIG. 2 is a schematic view of a piezoelectric transformer structure according to the present invention. After forming the high Qm piezoelectric ceramic green sheet, a plurality of inter-finger internal electrodes (a set of inter-finger internal electrode groups) 22 having the pattern shown in FIG. 4 were printed on the sheet. Next, after laminating the required number of sheets and hot pressing, the sheets were cut into predetermined dimensions and debindered. One more
Sintering is performed at 100 ° C. for 2 hours to obtain a piezoelectric ceramic rectangular plate 21. After sintering the piezoelectric ceramic rectangular plate 21, the input-side external electrodes 23a and 23b and the output-side external electrodes 24a and 2
4b are connected to the side ends of the interdigital finger electrodes 22 exposed on the side surfaces of the piezoelectric ceramic rectangular plate 21, respectively.
A piezoelectric transformer element was formed at approximately one-fourth from both ends in the length direction.

The device fabricated as above was heated at 150 ° C.
Electric field strength 1kV / mm for both input and output in silicone oil
For 15 minutes to obtain a piezoelectric transformer vibrator.

Finally, in order to evaluate the high power characteristics of the piezoelectric transformer, a 50 ohm resistor was used as a load,
The input / output power and heat generation were measured by sine wave driving, and the efficiency was obtained. For comparison, a Rosen-type piezoelectric transformer was prepared as a conventional example, and comparative evaluation was performed. Table 1 shows the evaluation results. The calorific value was measured at the vibration node, and the vibration speed was measured at the vibrator end face.

[0020]

[Table 1]

From Table 1, it is shown that the piezoelectric transformer of the present invention has a lower vibration speed and generates less heat and is more efficient than the conventional Rosen type.

[0022]

As described above, according to the present invention, it is possible to provide a high efficiency piezoelectric transformer with low vibration speed and low heat generation at the same input as compared with the conventional Rosen type. .

[Brief description of the drawings]

FIG. 1 is a perspective view of a piezoelectric transformer according to a first embodiment (Example 1) of the present invention.

FIG. 2 is a sectional view taken along the line II-II of FIG.

FIG. 3 is a perspective view of a piezoelectric transformer according to a second embodiment (Example 2) of the present invention.

FIG. 4 is a sectional view taken along the line IV-IV in FIG. 3;

FIG. 5 is a circuit block diagram of a general switching type AC adapter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Piezoelectric ceramic rectangular plate 12 Interdigital finger-shaped internal electrode 12-1, 12-2, 12-3, 12-4 Leader electrode 13a, 13b External electrode on the piezoelectric transformer input side 14a, 14b External electrode on the piezoelectric transformer output side 21 Piezoelectric Ceramic rectangular plate 22 Intersecting finger-shaped internal electrodes 23a, 23b External electrodes 24a, 24b on the input side of piezoelectric transformer 31 External electrodes 31 on the output side of piezoelectric transformer 31 Common mode choke coil for electromagnetic noise suppression on input side 32 Full-wave rectifier circuit 33 Smoothing capacitor 34 Switching circuit 35 Electromagnetic transformer 36 Rectifier circuit 37 Smoothing circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 41/107

Claims (2)

(57) [Claims] 1. A piezoelectric transformer using a resonance mode in a longitudinal direction of a piezoelectric ceramic rectangular plate, wherein each of a pair of partial regions substantially half in the longitudinal direction of the piezoelectric ceramic rectangular plate has a pair parallel to the longitudinal direction. Cross electrode internal electrode group, and a lead electrode extending from each of the cross finger internal electrode groups and being exposed on the side surface of the piezoelectric ceramic rectangular plate, wherein the cross finger internal electrode and the lead electrode are arranged in the thickness direction. A piezoelectric transformer further comprising a plurality of external electrodes arranged and connected to the extraction electrode on the side surface. 2. A piezoelectric transformer using a resonance mode in a longitudinal direction of a piezoelectric ceramic rectangular plate, wherein each of a pair of substantially partial regions in the longitudinal direction of the piezoelectric ceramic rectangular plate has a set parallel to the longitudinal direction. A pair of interdigital electrodes, the pair of interdigital electrodes having side ends exposed on the side surfaces of the piezoelectric ceramic rectangular plate, and at approximately one-quarter positions from both ends in the length direction. The piezoelectric transformer further comprises an external electrode for connecting to the side end, wherein a plurality of the interdigital electrodes are arranged in a thickness direction.