Housing for piezoelectric transformer device

Details Housing for piezoelectric transformer device Housing for piezoelectric transformer device

2000-03-17

2001-07-17

Budd, Mark O. (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

C310S348000

Reexamination Certificate

active

06262518

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a housing for a piezoelectric transformer device, e.g., a housing for mounting a Rosen piezoelectric transformer on a circuit board.
BACKGROUND ART
Recently, liquid crystal display panels have been widely used as display units in notebook personal computers which are easy to carry. Such a liquid crystal display panel incorporates a cold-cathode fluorescent lamp serving as a backlight for backlighting the panel. In order to light this cold-cathode fluorescent lamp, a high voltage of about 1 kV or more is required. To maintain emission of light, a voltage of about several hundred volts must be applied.
In such notebook personal computers and similar products, owing to their characteristics, the demand for compact inverters for backlights is high. In order to meet this demand, piezoelectric transformers are used as inverter components.
As such a piezoelectric transformer, the piezoelectric transformer device (to be referred to as the piezoelectric device hereinafter) having the multilayer structure proposed in Japanese Patent Application No. 8-52553 filed by the present applicant will be briefly described below with reference to
FIGS. 1
to
5
.
FIG. 1
is a perspective view showing the piezoelectric device having the multilayer structure previously proposed by the present applicant.
FIG. 2
is a front view of the piezoelectric device in FIG.
1
.
FIG. 3
is a plan view of the piezoelectric device in FIG.
1
.
A piezoelectric device
106
has an outer shape like the one shown in
FIGS. 1
,
2
, and
3
. The right and left half regions of the device will be respectively referred to as the second and first regions hereinafter.
Outer electrodes
101
and
102
as primary (input) electrodes are formed on the upper surface of the first region. An outer electrode
103
as a secondary (output) electrode is formed on the right end portion of the second region. Lead wires
105
are connected to the outer electrodes
101
,
102
, and
103
with solder portions
104
.
The internal structure of the first region will be described next.
FIG. 4
is a sectional view taken along a line I—I of the piezoelectric device in FIG.
3
.
FIG. 5
is a sectional view taken along a line II—II of the piezoelectric device in FIG.
3
.
As shown in
FIGS. 4 and 5
, in the first region, a plurality of inner electrodes
101
a
and
102
a
are alternately stacked, and the spaces between these inner electrodes are filled with the piezoelectric element
106
. As shown in
FIGS. 4 and 5
, in the first region, the plurality of inner electrodes
101
a
are connected to each other through a columnar conductor (to be referred to as an interlevel connection conductor hereinafter)
108
a
, and the plurality of inner electrodes
102
a
are connected to each other through an interlevel connection conductor
108
b
. Circular holes (to be referred to as holes hereinafter) are formed in the inner electrodes
101
a
and
102
a
so that the inner electrodes
101
a
and
102
a
are not connected to each other through the interlevel connection conductors
108
a
and
108
b.
The interlevel connection conductor
108
a
extends toward the upper surface of the first region and is connected to the outer electrode
101
.
Similarly, the interlevel connection conductor
108
b
extends toward the upper surface of the first region and is connected to the outer electrode
102
.
The piezoelectric device having the above multilayer structure is driven as follows. First, a high voltage is applied between the outer electrodes
101
and
102
to polarize the first region in the vertical direction (direction of thickness). A predetermined voltage is then applied between the outer electrode
101
or
102
and the outer electrode
103
to polarize the second region in the longitudinal direction. When an AC voltage is applied between the outer electrodes
101
and
102
of the device in the polarized state, the piezoelectric element
106
in the first region mechanically vibrates in accordance with the piezoelectric material constant unique to the piezoelectric element, the resonance characteristics, and the dimensions of the overall device. The vibrations are converted into a voltage by the piezoelectric element
106
in the second region. As a result, a boosted high AC voltage can be extracted from the outer electrode
103
.
When such a piezoelectric transformer is to be mounted on a circuit board, the transformer is generally housed in an insulating container (to be referred to as a housing hereinafter), and the housing is mounted on the circuit board for the following reason. As described above, when the piezoelectric transformer operates, the piezoelectric device itself mechanically vibrates. If this vibration is inhibited when the device is mounted on the circuit board, the output characteristics of the piezoelectric transformer deteriorate. Therefore, when the piezoelectric transformer is to be mounted, the device must be supported at portions corresponding to nodes of the vibrations of the piezoelectric device to prevent the vibrations of the device from being suppressed. In addition, since the secondary output of the piezoelectric transformer is set at a high voltage, the entire piezoelectric transformer must be covered with an insulating cover for safety reasons, i.e., preventing contact between the secondary output and other components and preventing the operator from receiving an electric shock.
An example of how the above piezoelectric device is housed in a housing having a general structure will be described with reference to
FIGS. 6
to
10
.
FIG. 6
is a perspective view showing a state in which the piezoelectric device having the multilayer structure previously proposed by the present applicant is housed in a general housing.
FIG. 7
is a plan view of the housing in FIG.
6
.
As shown in
FIGS. 6 and 7
, a housing
107
is a box-like resin container having an upper opening. The housing
107
has a volume enough to prevent the piezoelectric device
106
and the solder portions
104
of the lead wires
105
from protruding from the upper opening of the housing
107
when the piezoelectric device
106
is housed in the housing
107
. Projections
110
for fixing the piezoelectric device
106
in the housing
107
are formed on the inside of the housing
107
at positions corresponding to the nodes of the vibrations of the piezoelectric device
106
. In the case shown in
FIGS. 6 and 7
, the respective lead wires
105
extend outside through the holes (the holes may be slits) formed in the end faces in advance.
A method of housing the piezoelectric transformer in the housing
107
in this housed state will be described below, together with the mounted state of the housing on a circuit board.
FIG. 8
is a sectional view taken along a line III—III of the housing in FIG.
6
.
FIG. 9
is a sectional view taken along a line IV—IV of the housing in FIG.
6
.
FIG. 10
is a perspective view showing an example of how the piezoelectric transformer is mounted on the circuit board.
When the piezoelectric device
106
is to be housed in the housing
107
, the projections
110
are first coated with an adhesive
109
. As shown in
FIGS. 8 and 9
, the piezoelectric device
106
is then housed in the housing
107
such that the nodes of the vibrations of the piezoelectric device
106
coincide with the projections
110
. With this process, the piezoelectric can be supported in the housing
107
at the portions corresponding to the nodes of vibrations.
The housing is mounted on the circuit board as follows. After the adhesive
109
applied to the projections
110
is hardened, the housing
107
is turned upside down and mounted on a circuit board
112
, as shown in FIG.
10
. The housing
107
is fixed to the circuit board
112
with an adhesive
111
. The respective lead wires
105
extending through the above holes are connected to the circuit board
112
by soldering.
Other methods of supporting the piezoelectric device and mounting it on the circuit board, other than those described above, ha

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