Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-04-12
2002-01-29
Sircus, Brian (Department: 2839)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S359000
Reexamination Certificate
active
06342752
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a piezoelectric transformer element suitably used to, e.g., turn on a cold cathode tube, and a method of housing the same.
BACKGROUND ART
A cold cathode tube is generally used for the backlight of the liquid crystal display of a notebook personal computer or the like. This cold cathode tube requires high voltage of about 1 kV to turn it on, and voltage of several hundred V to keep it on. The cold cathode tube can be kept on at voltage much lower than the voltage required to turn it on. The operation characteristics of the cold cathode device are similar to the operation characteristics of a piezoelectric transformer element, so that an inverter having such a piezoelectric transformer element is recently being used as a power supply for the cold cathode tube.
As the piezoelectric transformer element, a Rosen piezoelectric transformer element like the one shown in
FIG. 21
is widely used.
FIG. 21
is a perspective view showing a general Rosen piezoelectric transformer element. In
FIG. 21
, a piezoelectric transformer element
106
has a rectangular shape, its left half in
FIG. 21
serves as an input region, and its right half in
FIG. 21
serves as an output region. External electrodes
101
and
102
, as input electrodes for applying input voltage, are formed on the upper and lower surfaces of the input region. An external electrode
103
, as an output electrode for extracting boosted AC voltage, is formed on the end face of the output region. When an AC voltage (input voltage) having a resonance frequency determined by the material and length of the piezoelectric transformer element
106
is applied between the external electrodes
101
and
102
, the piezoelectric transformer element
106
mechanically vibrates and resonates in the longitudinal direction. The mechanical vibration generates boosted AC voltage between either one of the external electrodes
101
and
102
as a ground electrode common to the input and output sides, and the external electrode
103
. The boosting ratio as the ratio of the output voltage to the input voltage is proportional to the ratio of the distance between the output electrodes and the distance between the input electrodes.
As the piezoelectric transformer element, a single-plate piezoelectric transformer element as the one shown in
FIG. 21
has conventionally been used. In an inverter having such a single-plate piezoelectric transformer element, the boosting ratio is about 10 at most. To turn on a cold cathode tube for a notebook personal computer, a boosting winding transformer must be provided on the input stage of the piezoelectric transformer element. Accordingly, to obtain a higher boosting ratio than that of the single-plate piezoelectric transformer element, and to eliminate the winding transformer from the input stage, a piezoelectric transformer element having a structure in which the distance between internal electrodes in the input region of piezoelectric layers is decreased, i.e., the thin piezoelectric layers and the internal electrodes are stacked, is formed.
In this multilayer piezoelectric transformer element, the electrodes in the input region must be electrically connected. As the connection method, for example, Japanese Patent Laid-Open No. 7-302938 discloses the method in which electrodes
305
for electrically connecting internal electrodes
301
a
and
302
a
in the input region between external electrodes
301
and
302
are formed at the corners of the side or end faces of a piezoelectric transformer element
306
, as shown in FIG.
24
. In Japanese Patent No. 8-52553, the present applicant proposed a method of alternately connecting a plurality of internal electrode layers stacked inside the input region of a piezoelectric transformer element by two columnar conductors (to be referred to as interlevel connection conductors hereinafter).
When such a piezoelectric transformer element is mounted on a circuit board, the piezoelectric transformer element is often used in a housing so as not to expose the high-voltage portion. In a conventional multilayer piezoelectric transformer element, lead wires are bonded with solder or conductive adhesive to external electrodes formed on the upper and lower surfaces of the input region, similar to the external electrodes
101
and
102
in FIG.
21
. Although the piezoelectric transformer element has the advantage of a small thickness, mounting the piezoelectric transformer element connected to the lead wires requires a margin of at least the diameter of the lead wire between the element and the board, and a space for at least the diameter of the lead wire above the piezoelectric transformer element. As a result, the thickness of the housing increases, and the advantage of the thin piezoelectric transformer element cannot be fully exploited.
The housing must be designed to have a large thickness in consideration of the diameter of the lead wire and the thickness of solder or conductive adhesive for bonding the lead wire. The thickness of the piezoelectric transformer module upon mounting, therefore increases with “thickness for the bonding space”.
To solve this problem, for example, according to Japanese Patent Laid-Open No. 9-116250, input electrodes
201
and
202
are formed on upper and lower surfaces on the primary side of a piezoelectric transformer element
206
and extended to the side surfaces of the element to form lead electrodes
201
a
and
202
a
so as to fix the piezoelectric transformer element
206
to a housing
205
by terminals
210
A and
210
B at node positions of the side surfaces in the longitudinal direction, as shown in
FIGS. 22 and 23
. Output electrodes
204
are formed on the two side surfaces of the element on the secondary side. This structure can make the housing thin and simplify the mounting process.
However, with recent developments in notebook personal computers or portable information terminals, demands have arisen for smaller-size apparatus. Along with this, the difference in size between the liquid crystal display and the main body is diminishing. Since an inverter for the backlight of the liquid crystal display is generally arranged around the liquid crystal display, the inverter must be narrowed as the outer dimension of the main body of a personal computer or the like is downsized.
By the conventional housing method, however, the housing or module can be made thin, but the housing cannot be narrowed.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a piezoelectric transformer element whose height and width necessary for mounting can be decreased, and a method of housing the same.
To achieve the above object, a piezoelectric transformer element of the present invention is characterized by the following arrangement.
A piezoelectric transformer element with a multilayer structure having an input region which is polarized in a direction of thickness and has input electrodes, and an output region which is polarized in a longitudinal direction and has an output electrode is characterized by comprising a plurality of internal electrodes as the input electrode which are formed between a plurality of piezoelectric layers, first and second external electrodes formed on an end face of the piezoelectric transformer element in the longitudinal direction on the input region side, and an external electrode formed on an end face of the piezoelectric transformer element in the longitudinal direction on the output region side, wherein the plurality of internal electrodes are alternately connected to the first and second external electrodes every other layer, and the external electrodes are electrodes for applying input voltage. With this structure, when the piezoelectric transformer element is mounted on another member, the element can be connected at only its end face in the longitudinal direction, and the height and width (width of widthwise direction of the element) necessary for mounting can be reduced.
The element preferably further comprises third and fourth external electrod
Fujimura Takeshi
Ishikawa Katsuyuki
Kataoka Masako
Tsukamoto Keizo
Yamakawa Takahiro
Burns Doane , Swecker, Mathis LLP
Sircus Brian
Taiheiyo Cement Corporation
Zarroli Michael C.
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