U.S. patent application number 09/823551 was filed with the patent office on 2001-10-04 for piezoelectric transformer.
This patent application is currently assigned to Taiyo Yuden Co., Ltd.. Invention is credited to Inomata, Yasuyuki, Ishii, Shigeo, Kishi, Hiroshi, Watanabe, Yoshiyuki.
Application Number | 20010026113 09/823551 |
Document ID | / |
Family ID | 18610652 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010026113 |
Kind Code |
A1 |
Watanabe, Yoshiyuki ; et
al. |
October 4, 2001 |
Piezoelectric transformer
Abstract
The piezoelectric transformer obtains large output powers by way
of reducing the heat generation. The piezoelectric transformer
includes one or more input parts and an output part. Each of the
input parts is formed of alternately stacked piezoelectric sheets
and internal electrodes. Each piezoelectric sheet has a first
region on which the internal electrode is formed and a second
region on which no internal electrode is formed. Each of the input
parts includes means for reducing stress concentration around
boundary regions between the first and the second regions.
Inventors: |
Watanabe, Yoshiyuki; (Tokyo,
JP) ; Kishi, Hiroshi; (Tokyo, JP) ; Inomata,
Yasuyuki; (Tokyo, JP) ; Ishii, Shigeo; (Tokyo,
JP) |
Correspondence
Address: |
SAHAN ISLAM, ESQ.
ROSENMAN & COLIN LLP
575 Madison Avenue
New York
NY
10022-2585
US
|
Assignee: |
Taiyo Yuden Co., Ltd.
16-20 Ueno 6-chone, Taito-ku,
Tokyo
JP
J
|
Family ID: |
18610652 |
Appl. No.: |
09/823551 |
Filed: |
March 30, 2001 |
Current U.S.
Class: |
310/359 |
Current CPC
Class: |
H01L 41/107
20130101 |
Class at
Publication: |
310/359 |
International
Class: |
H01L 041/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 30, 2000 |
JP |
2000-095797 |
Claims
What is claimed is:
1. A piezoelectric transformer comprising: one or more input parts;
and an output part, wherein each of the input parts is formed of
alternately stacked piezoelectric sheets and internal electrodes
and each of the piezoelectric sheets has a first region on which
each of the internal electrodes is formed and a second region on
which no internal electrode is formed, and wherein each of the
input parts includes means for reducing stress concentration around
boundary regions between the first and the second regions.
2. The piezoelectric transformer of claim 1, wherein the
stress-reducing means is non-overlapping portions of two
neighboring internal electrodes.
3. The piezoelectric transformer of claim 2, wherein the
stress-reducing means is disposed along a periphery of each of the
internal electrodes.
4. The piezoelectric transformer of claim 3, wherein the periphery
of each of the neighboring internal electrodes is different from
that of the neighboring internal electrodes.
5. The piezoelectric transformer of claim 3, wherein the
peripheries of the neighboring internal electrodes have an
identical shape and the neighboring internal electrodes are shifted
from each other.
6. The piezoelectric transformer of claim 3, wherein the
neighboring internal electrodes have an identical shape but with
different size.
7. The piezoelectric transformer of claim 2, wherein each of the
internal electrodes in the input part include a plurality of
openings, the neighboring internal electrodes being disposed for
the openings thereof not to completely overlap with each other.
8. The piezoelectric transformer of claims 1, wherein the
piezoelectric transformer is a Rosen-type piezoelectric
transformer.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a piezoelectric
transformer; and, more particularly, to a laminated piezoelectric
transformer for use in such power sources as converters and
inverters.
BACKGROUND OF THE INVENTION
[0002] Piezoelectric transformers feature smaller sizes and easily
obtainable higher efficiencies than conventional electromagnetic
transformers. For such reasons, piezoelectric transformers are
gaining popularity as step-up transformers, e.g., backlight power
sources of liquid crystal display (LCD) monitors. However,
step-down transformers are more frequently used in power supplies
than step-up transformers.
[0003] It is preferable that a piezoelectric transformer have such
characteristics as high output power, less heat generation, small
size and higher efficiency. However, increasing the output power of
a conventional piezoelectric transformer gives rise to the
increased heat generation, which in turn reduces the output
thereof.
[0004] Output power of a piezoelectric transformer is basically
determined by a mechanical vibration velocity thereof. In order to
obtain a high mechanical vibration velocity, it is preferable to
construct an input (driving) part of a piezoelectric transformer to
have a configuration capable of generating a large vibration.
[0005] Generation of large vibration can be achieved by
constructing the electrodes in a laminated structure or by
increasing the area of the electrodes. However, large vibrations in
a piezoelectric transformer cause an increase in crystallographic
and electric losses, resulting in an increased heat generation
which in turn reduces the output power of the piezoelectric
transformer.
SUMMARY OF THE INVENTION
[0006] It is, therefore, an object of the present invention to
provide a piezoelectric transformer capable of obtaining large
output powers by way of reducing the heat generation.
[0007] In accordance with the present invention, there is provided
a piezoelectric transformer including: one or more input parts; and
an output part, wherein each of the input parts is formed of
alternately stacked piezoelectric sheets and internal electrodes
and each piezoelectric sheet has a first region on which the
internal electrode is formed and a second region on which no
internal electrode is formed, and wherein each of the input parts
includes means for reducing stress concentration around boundary
regions between the first and the second regions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The above and other objects and features of the present
invention will become apparent from the following description of
preferred embodiments with conjunction to the accompanying drawings
in which:
[0009] FIG. 1 is a fragmentary perspective view setting forth a
laminated body incorporated in a piezoelectric transformer in
accordance with a first embodiment of the present invention;
[0010] FIG. 2 shows a perspective view illustrating the
piezoelectric transformer in accordance with a first embodiment of
the present invention;
[0011] FIG. 3A offers a schematic sectional view depicting a input
part in the piezoelectric transformer shown in FIG. 1, with other
portions omitted;
[0012] FIGS. 3B and 3C provide graphs as in FIG. 3A portraying a
displacement of the piezoelectric transformer;
[0013] FIG. 3D represents a schematic sectional view similar to
that of FIG. 3A and depicting a input part of a comparative
piezoelectric transformer;
[0014] FIG. 3E presents a graph as in FIG. 3D delineating a
displacement of the comparative piezoelectric transformer;
[0015] FIG. 4 shows graphs representing temperature increment as a
function of an input power in the piezoelectric transformers of
FIG. 3A and in the comparative piezoelectric transformer of FIG.
3D;
[0016] FIG. 5 offers a fragmentary perspective view setting forth a
laminated body incorporated in a piezoelectric transformer in
accordance with a second embodiment of the present invention;
[0017] FIG. 6 provides a schematic plan view illustrating an
internal electrode in a input part of a piezoelectric transformer
in accordance with a third embodiment of the present invention;
and
[0018] FIG. 7 represents a schematic cross sectional view depicting
a Rosen-type piezoelectric transformer in accordance with a fourth
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0019] It has been known that heat generation in a piezoelectric
transformer mainly occurs at the input (driving) part thereof. The
inventors of the present invention have therefore conducted
experiments to investigate the heat generation mechanism and found
that most of the heat is generated at the boundary regions of the
electrodes of the input part, where the deformed regions under the
electrodes are in contact with the undeformed regions therearound.
Stresses are concentrated at the boundary between the deformed and
the undeformed regions and, therefore, a large amount of heat is
generated due to mechanical friction taking place thereat. It has
been also found that heat generation at the boundary regions is
mainly determined by the mechanical factor, i.e., stress, rather
than other factors, e.g., crystalline structure. Accordingly, high
efficient piezoelectric transformers can be obtained by restraining
the heat generation by way of reducing the stress concentration at
the boundary regions.
[0020] A first preferred embodiment of the present invention will
now be described with reference to FIGS. 1 to 4. In a fabrication
of a piezoelectric transformer in accordance with the first
preferred embodiment of the present invention, a laminated body 34
is formed as shown in FIG. 1, the laminated body 34 being provided
with an output (power generating) part 20 disposed between two
input (driving) parts 10.
[0021] Each of the input parts 10 includes two laminated
piezoelectric sheets 14, 16 each having an internal electrode 12 at
the center of a top surface thereof. The overall shape of each
internal electrode 12 is circular, but there is provided at the
periphery of each internal electrode 12 a stress-relieving pattern
12A having a saw-toothed shape. The laminated body 34 is preferably
formed such that the peripheries of the internal electrodes 12 on
the sheets 14, 16 do not completely overlap with each other when
viewed from the top. Specifically, two stress-relieving patterns
12A on the sheets 14 and 16 are formed to have different shapes or
if the stress-relieving patterns 12A have the identical shape, two
internal electrodes are disposed on the sheets 14 and 16 such that
they are rotated and/or shifted from one another in order for the
stress-relieving patterns 12A not to completely overlap with each
other.
[0022] The internal electrodes 12 formed on the laminated
piezoelectric sheets 14, 16 include terminals 14A and 16A extending
toward the backside and the front side of the laminated body 34,
respectively. In other words, the terminals 14A and 16A of the
neighboring internal electrodes 12 extend along the backward and
forward direction from the internal electrodes 12.
[0023] The output (power generating) part 20 includes, e.g., six
pairs of laminated piezoelectric sheets 24 and 26, each of
laminated piezoelectric sheets 24 and 26 having an internal
electrode 22 at the substantial center of a top surface thereof.
The internal electrodes 22 formed on the pair of laminated
piezoelectric sheets 24 and 26 include terminals 24A and 26A
extending toward the light side and the left side of the laminated
body 34, respectively. In other words, the terminals 24A and 26A of
the neighboring internal electrodes 22, respectively, extend along
the right and the left directions from the internal electrodes
22.
[0024] The laminated body 34 further includes two insulation bare
sheets 30 for separating the upper and the lower input parts 10
from the output part 20, the insulation bare sheets 30 having no
electrodes thereon being disposed between the input parts 10 and
the output part 20. The laminated body 34 is further provided with
two protective insulation sheets 32 disposed on top and under
bottom thereof. Piezoelectric, e.g., PZT, green sheets are used for
the sheets 14, 16, 24, 26. Additionally, the internal electrodes
12, 22 and the terminals 14A, 16A, 24A and 26A are formed of, e.g.,
an Ag or Pd alloy.
[0025] All the sheets constituting the piezoelectric transformer
are compressed after being stacked as shown in FIG. 1. Thereafter,
a binder removing and sintering process are performed and then
external electrodes 40A, 40B, 42A and 42B are formed on the
sintered body as shown in FIG. 2. In this example, the terminals
14A of the input parts 10 are connected to an external electrode
40A and the terminals 16A thereof are connected to an external
electrode 40B as illustrated in FIG. 2. The terminals 24A of the
output part 20 are connected to an external electrode 42A and the
terminals 26A thereof are connected to an external electrode 42B.
The external electrodes 40A, 40B, 42A and 42B are formed of a
conductive material, e.g., Ag. Next, a poling of the sintered body
is performed through the use of external electrodes formed thereon.
For instance, the poling of the sintered body is achieved by
applying an electric field of 2 KV/mm between the external
electrodes 40A and 40B and between 42A and 42B at 100.degree. C.
for 10 min, thereby obtaining a piezoelectric transformer 44.
[0026] Thereafter, the piezoelectric transformer thus obtained has
been compared with comparative samples of conventional
piezoelectric transformers having no stress-relieving patterns at
the internal electrodes of the input parts. FIGS. 3A and 3D
respectively depict schematic cross sectional views of the input
part 10 of the piezoelectric transformer 44 in accordance with the
first embodiment of the present invention and a input part 10' of a
comparative piezoelectric transformer. As described above, the
stress-relieving patterns 12A of the internal electrodes 12 of the
input part 10 are provided with irregular edges not completely
overlapping with each other. If there exists non-overlapping
regions at the edges of the internal electrodes 12 as shown in FIG.
3A, deformation in the piezoelectric sheets due to the upper and
the lower electrodes 12 will occur along the lines HA and HB as
shown in FIG. 3B. The overall deformation of the piezoelectric
sheet due to the internal electrodes 12 of FIG. 3A then will be the
average of the deformation along the curves HA and HB, having less
steep transition of deformation as shown in FIG. 3C. Therefore,
stress will be distributed in wider regions around the periphery of
the internal electrodes 12. On the other hand, since the internal
electrodes 12' of the input part of the conventional piezoelectric
transformers are completely overlapped as shown in FIG. 3D, the
transition from the deformed region to the non-deformed region
sharply occurs as shown in FIG. 3E. In other words, the stress is
concentrated around the periphery of the internal electrodes
12'.
[0027] FIG. 4 shows graphs representing temperature increment as a
function of an input power in the piezoelectric transformer of the
present invention and the prior art, wherein the horizontal and the
vertical axes indicate the input power (W) and the temperature
variation [.DELTA.t (.degree. C.)], respectively. Curves GA and GB
correspond to the piezoelectric transformer 44 of the present
invention and the comparative sample, respectively. As can be noted
from the curves that the temperature increase of the inventive
piezoelectric transformer is lower than that of the comparative
piezoelectric transformer.
[0028] FIG. 5 describes a laminated body 34 incorporated in a
piezoelectric transformer in accordance with a second embodiment of
the present invention, wherein like reference numerals designate
like parts shown in FIG. 1. In the laminated body 34 of this
embodiment, each input part 10 includes two piezoelectric sheets
14, 16 having internal electrodes 12B and 12C disposed on top
thereof. The internal electrodes 12B and 12C have different size.
For example, the internal electrode 12C is formed to have a
diameter larger than that of the internal electrode 12B. As a
result, the transition between the deformed and the undeformed
regions occurs less steeply and therefore the stress concentration
can be ameliorated, resulting in the reduced heat generation.
[0029] FIG. 6 illustrates an internal electrode 50 incorporated in
an input part of a piezoelectric transformer in accordance with the
third embodiment of the present invention. The internal electrode
50 includes a plurality of openings 52 each of which is arranged to
have an enlarged diameter as moving from the center to the
periphery of the internal electrodes 50. By arranging the neighbor
internal electrodes 50, the openings 52 of the electrodes 50 do not
completely overlap with each other, in such a way that the heat
generation can be effectively reduced as in the first and the
second embodiments of the present invention.
[0030] Referring to FIG. 7, there is illustrated a Rosen-type
piezoelectric transformer 60 in accordance with a fourth embodiment
of the present invention, wherein the piezoelectric transformer 60
includes an input part and an output part at the left and the right
hand sides thereof. The input part having two external electrodes
62, 64 are placed at the top and the bottom surfaces thereof,
respectively, and a number of internal electrodes 70. The output
part having an external electrode 66 formed on a side surface
thereof. In the input part, the neighbor internal electrodes are
shifted from each other in such a way that they do not completely
overlap with each other. As a result reduction of heat generation
can be effected as in the previous embodiments.
[0031] While the invention has been shown and described with
respect to the preferred embodiments, it will be understood by
those skilled in the art that various changes and modifications may
be made without departing from the spirit and scope of the
invention as defined in the following claims.
* * * * *