Electronic component

Details Electronic component Electronic component

1999-07-16

2001-01-09

Easthom, Karl D. (Department: 2832)

Electrical resistors

Resistance value responsive to a condition

Current and/or voltage

C338S316000, C338S232000, C338S234000, C338S0220SD

Reexamination Certificate

active

06172593

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to electronic devices employing therein an electronic element with opposite electrodes on its principal planes, and more particularly, to electronic modules with an elastic support mechanism for an electronic element mounted therein having spring contact pieces in contact with respective electrodes of the electronic element for elastic support of the element as interposed therebetween.
2. Description of the Prior Art
Conventionally, many electronic devices include positive thermistor devices for use in current limiter circuitry. Thus, thermistor devices have been widely used in the manufacture of several types of electric circuitry or modules, including motor activation controller circuitry for electric refrigerators, electronic demagnetization circuitry for television receivers, monitor display tube units, and other applications.
One typical configuration of a prior art positive thermistor device is shown in
FIGS. 13 and 14
, wherein this device is generally designated by the numeral 1. This conventional positive thermistor device I essentially consists of a casing body or base
3
, a positive thermistor element
4
held therein, a pair of first and second terminal members
5
,
6
, and a lid or cover
2
attached to the base
3
to close the upper opening thereof.
As shown, the positive thermistor element
4
exhibits a disk-like shape having opposite surfaces on which first and second electrodes
7
,
8
are disposed respectively. This positive thermistor element
4
is centrally inserted into the inside space of the base
3
, with the electrodes
7
,
8
facing the right and left sides thereof, as shown in FIG.
14
.
The first and second terminal members
5
,
6
are assembled within the inside space of casing base
3
in such a way that these members
5
,
6
support both sides of the opposed electrodes
7
,
8
of the positive thermistor element
4
. Each terminal member
5
,
6
may be an elastic conductive plate of a chosen metallic material. The first terminal member
5
includes a pair of spring contact pieces
9
,
10
having a W-shaped profile as a whole, and also a hollow tube socket
11
with a longitudinal gap for receiving therein a known connector pin (not shown) associated therewith to provide electrical connection therebetween. A wave shaped plate constituting the W-shaped spring contact pieces
9
,
10
and the socket
11
may be integrally formed in the terminal member
5
by known welding or caulking techniques. The second terminal member
6
is similar in structure to the first terminal
5
; it has W-shaped spring contact pieces
12
,
13
and connector-pin socket
14
.
After assembly within the casing base
3
, the spring contact pieces
9
,
10
of the first terminal member
5
serve to apply compressive force onto the first electrode
7
due to its inherent elastic nature. Similarly, the spring contact pieces
12
,
13
of the second terminal member
6
apply compressive force to the second electrode
8
. This may enable the positive thermistor element
4
to be elastically supported or suspended between the terminal members
5
,
6
while the element
4
is interposed between one pair of spring contact pieces
9
,
10
and the other pair of contact pieces
12
,
13
.
Additionally, a mica plate
15
may be disposed around the outer periphery of the positive thermistor element
4
. This mica plate
15
exhibits a circular shape. When engaged with the outer periphery of thermistor element
4
, this plate
15
acts to facilitate appropriate positioning (hereinafter referred to as “position-determination”) of thermistor
4
inside base
3
.
After the positive thermistor element
4
and terminal members
5
,
6
are assembled within the casing base
3
, the cover
2
is attached thereto so that it closes the upper opening of the casing body
3
. This cover
2
is a rectangular plate member having at its two corresponding corners two holes
16
,
17
to permit insertion of external connector pins into the sockets
11
,
14
through these holes respectively.
Another prior known positive thermistor device
1
a
is shown in
FIGS. 16
to
18
. As is readily seen by comparison of the illustration of
FIG. 16
to that of
FIG. 14
, this prior art device is similar in structure to the previous device; accordingly, like reference characters are used to designate like parts or components with a redundant explanation thereof being omitted herein.
As can be seen from
FIG. 16
, the positive thermistor device
1
a
is structurally different from that of
FIG. 14
to the extent that a first terminal member
5
a
has a W-shaped pair of spring contact pieces
9
a,
10
a
extending vertically, rather than horizontally as in the previous prior art device
1
, best shown in
FIG. 14
, thereby preventing these contact pieces
9
a,
10
a
from directly opposing their associated spring contact pieces
12
,
13
of the other, second terminal member
6
. Such vertical facing relation of spring contact pieces
9
a
,
10
a
versus the opposite spring contact pieces
12
, may also be seen in
FIGS. 17 and 18
.
FIGS. 17 and 18
show a plan view and side view, respectively, of the device shown in FIG.
16
.
With the prior art positive thermistor devices
1
,
1
a,
after a long time has elapsed after installation thereof, the structure of the positive thermistor element
4
may become physically degraded. If this is the case, abnormal heat generation may take place therein causing sparks to occur during operation, which results in the positive thermistor element
4
being destroyed due to occurrence of such sparks. When the thermistor element
4
is destroyed, it breaks into several fragments that can disperse within the closed inside space as defined by the casing base
3
and cover
2
attached thereto.
Such a “malfunction mode” phenomenon can lead to a more serious malfunction mode, which will be discussed in more detail below with reference to
FIGS. 15A and 15B
for the positive thermistor device of
FIGS. 13 and 14
, and with reference to
FIGS. 19
to
21
for the device la shown in
FIGS. 16
to
18
, respectively.
In the positive thermistor device
1
of
FIGS. 13 and 14
, when sparks occur, the resulting positive thermistor element
4
experiences occurrence of several cracks
18
therein, as shown in FIG.
15
A. Even under such a condition, specific cracked portions
19
, each of which is elastically supported by the opposed spring contact pieces
9
,
10
(or
12
,
13
) at its opposite sides, continue to stably be held there at as shown in
FIG. 15B
, while the remaining fragments disperse. Accordingly, a power supply may continuously be fed by way of such residual components
19
of the thermistor element
4
, causing these residual components
19
and their associative spring contact pieces
9
,
10
,
12
,
13
to melt, in turn producing an alloy that exhibits some conductivity. As a result, an electrical short can be formed between the terminal members
5
,
6
. This adversely serves to accelerate further generation of abnormal heat. This will possibly force the device to go into a further malfunction mode which can, in turn, lead to unwanted softening of the casing base
3
.
Furthermore, in the positive thermistor device
1
, since the mica plate
15
is arranged therein, certain peripheral portions
20
of the positive thermistor element
4
which are directly in contact with the mica plate
15
tend to also be prevented from flying away as fragments, in most cases. Such peripheral portions
20
also contribute to the formation of alloy together with the aforementioned portions
19
being elastically supported by spring contact pieces
9
,
10
,
12
,
13
, with the result of increasing the amount of materials for producing the alloy. This may exacerbate the malfunction of the device, which may cause the softening of base
3
to become more serious.
On the other hand, in the positive thermistor device la shown in
FIGS. 16
to
18
, the positive thermistor element
4
e

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