Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-04-12
2001-12-25
Budd, Mark (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S351000, C310S359000, C310S366000
Reexamination Certificate
active
06333589
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric transformer and a method for manufacturing the same, and more specifically to a laminated piezoelectric transformer advantageously incorporated in a small-sized rectifying power supply which is required to have a small size, a light weight and high reliability, and a method for manufacturing the same.
2. Description of Related Art
In the prior art, a solenoid type electromagnetic transformer was used as a step-down transformer in a so-called AC adapter for supplying an electric power to various battery-cell-driven electronic instruments from a power-frequency voltage distribution system. The electromagnetic transformer is composed of a magnetic core and a conducting wire wound around the magnetic core by a large number of turns. Because of this construction, it is actually difficult to realize a small-size, light-weight electromagnetic transformer.
On the other hand, a piezoelectric transformer utilizing a piezoelectric effect, which is completely different from the electromagnetic transformer in operation principle, has been provided.
The piezoelectric transformer is discussed in for example C. A. Rosen, “Ceramic Transformer”, Proc. of Electronic Component Symposium, 1957. In this connection, various mounting or packaging methods for the piezoelectric transformer have been proposed in the prior art (See for example, Japanese Patent Application Pre-examination Publication Nos. JP-A-08-274382 (an English abstract is available from the Japanese Patent Office and the content of the English abstract is incorporated by reference in its entirety into this application) and JP-A-08-298213 (which corresponds to U.S. Pat. No. 5,747,916, the content of which is incorporated by reference in its entirety into this application).
Now, an example of the Rosen type piezoelectric transformer which is a typical prior art piezoelectric transformer, will be described with reference to
FIG. 1A
which is a diagrammatic perspective view illustrating the prior art Rosen type piezoelectric transformer mounted on a support member, and which corresponds to
FIG. 13
of JP-A-08-274382, and also with reference to
FIG. 1B
which is a diagrammatic sectional view taken along the line A—A in
FIG. 1A
but showing a condition that the piezoelectric transformer is supported within a housing.
Referring to
FIGS. 1A and 1B
, the shown prior art Rosen type piezoelectric transformer includes a piezoelectric ceramic plate
510
in the form of an elongated plate, which is divided into a driver section
51
and a generator section
52
. The driver section
51
is polarized in a thickness direction of the piezoelectric ceramic plate
510
, and therefore includes a pair of planar electrodes
511
and
512
formed on upper and lower surfaces of the piezoelectric ceramic plate
510
, respectively, so as to substantially cover the whole of the upper and lower surfaces in the driver section
51
. On the other hand, the generator section
52
is polarized in a lengthwise direction of the piezoelectric ceramic plate
510
, and an end electrode
515
is formed on the generator section side end surface of a pair of end surfaces in the lengthwise direction. Furthermore, support members
520
are provided each to surround the piezoelectric ceramic plate
510
along a direction orthogonal to the lengthwise direction of the piezoelectric ceramic plate
510
.
The piezoelectric transformer having the above mentioned construction is used for a voltage step-up. Now, an operation principle of the piezoelectric transformer will be described.
If an AC voltage is applied from an external between the upper and lower planar electrodes
511
and
512
of the driver section
51
, namely, between a pair of input terminals
517
and
518
connected to the planar electrodes
511
and
512
, respectively, the driver section
51
is caused to vibrate in the lengthwise direction because of a piezoelectric lateral effect, in accordance with the magnitude of the applied AC voltage.
As a result, lengthwise direction vibration occurs in the piezoelectric ceramic plate
510
, so that because of a piezoelectric longitudinal effect of the vibration, a stepped-up voltage having the same frequency as that of the input voltage is generated between the planar electrode
511
or
512
of the driver section
51
and the end electrode
515
of the generator section
52
(in the example shown in
FIG. 1A
, between the planar electrode
512
and the end electrode
515
).
Next, a packaging of the above mentioned Rosen type piezoelectric transformer will be described. Referring to
FIG. 1B
, in order to support the piezoelectric transformer vibrating in the lengthwise direction because of the piezoelectric lateral effect, it is important to support the piezoelectric transformer without attenuating the vibration. In ordinary cases, the support member
520
is positioned in a region which becomes a node of the vibration called a “&lgr; mode”.
In this prior art example, the support member
520
is formed of an elastic material such as rubber. Namely, two elastic members
520
formed of rubber are mounted to surround the piezoelectric ceramic plate
510
at vibration node positions, and an outer surface of the elastic members
520
is fixed to an inner surface of a housing
521
which accommodates therein the piezoelectric ceramic plate
510
. Thus, the piezoelectric ceramic plate
510
is packaged.
Now, another structure of the package of the Rosen type piezoelectric transformer will be described with reference to
FIG. 2A
which is a diagrammatic perspective view illustrating another example of the Rosen type piezoelectric transformer mounted on a support member, and which substantially corresponds to those disclosed in JP-A-09-298213 and U.S. Pat. No. 5,747,916, and also with reference to
FIG. 2B
which is a diagrammatic sectional view taken along the line B—B in
FIG. 2A
but showing a condition that the piezoelectric transformer is supported within a housing. In
FIGS. 2A and 2B
, elements corresponding in function to those shown in
FIGS. 1A and 1B
are given the same reference numerals, and explanation will be omitted for simplification of description.
As will be seen from comparison between
FIGS. 1A and 1B
and
FIGS. 2A and 2B
, the piezoelectric transformer shown in
FIGS. 2A and 2B
is substantially the same as that shown in
FIGS. 1A and 1B
in construction and in operation principle, excluding that the support member
520
is constituted of a spring in place of the rubber.
Next, a heat-dissipating technology, which is important in a high-power piezoelectric transformer, will be described with reference to Japanese Utility Model Application Pre-examination Publication No. JP-U-06-82870.
FIG. 3
is a diagrammatic perspective view illustrating the Rosen type piezoelectric transformer, disclosed in JP-U-06-82870, having a heat-dissipating plate mounted thereon for dissipating heat generated in the piezoelectric transformer.
The piezoelectric transformer shown in
FIG. 3
is substantially the same as the piezoelectric transformers mentioned above in fundamental construction and in operation principle. Therefore, in
FIGS. 3
, elements corresponding in function to those shown in
FIGS. 1A and 1B
are given the same reference numerals, and explanation will be omitted for simplification of description.
The piezoelectric transformer shown in
FIG. 3
is different from the piezoelectric transformers mentioned above in that, in order to dissipate heat generated in the piezoelectric transformer, the piezoelectric transformer shown in
FIG. 3
has a heat-dissipating thin plate
806
which is formed of an aluminum thin plate and which is bonded by an epoxy resin bonding agent to a node where a heat generation becomes maximum.
In the above, the package structures of the Rosen type piezoelectric transformer have been described. In addition, a piezoelectric transformer having an operation principle different from that of the Rosen type piezoelectric transformer, has be
Inoi Takayuki
Saito Susumu
Budd Mark
NEC Corporation
Sughrue & Mion, PLLC
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