Positive temperature coefficient thermistor

Details Positive temperature coefficient thermistor Positive temperature coefficient thermistor

2002-01-22

2003-09-09

Easthom, Karl D. (Department: 2832)

Electrical resistors

Resistance value responsive to a condition

Current and/or voltage

C338S234000, C338S235000, C338S236000

Reexamination Certificate

active

06617955

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to positive temperature coefficient thermistors preferably for use in demagnetizing circuits included in electric appliances such as color television sets. More particularly, the present invention relates to positive temperature coefficient thermistors, in each of which a positive temperature coefficient thermistor element supported by metal terminals is included in a case and portions of the metal terminals extend outside of the case.
2. Description of the Related Art
FIG. 6
shows a positive temperature coefficient thermistor of the two-terminal type as an example of the related art. In this positive temperature coefficient thermistor, a positive temperature coefficient thermistor element
22
is supported by a pair of metal terminals
23
a
and
23
b
and is contained in a plastic case
21
.
The case
21
includes a main body
24
having an open top portion and a cover member
25
attached to an opening
24
a
of the main body
24
.
The metal terminals
23
a
and
23
b
are formed from a metal plate having a spring-like property. As shown in
FIGS. 6 and 7
, the metal terminals
23
a
and
23
b
include two springs
26
a
and
26
b
supporting the positive temperature coefficient thermistor element
22
interposed therebetween, supporting members
27
a
and
27
b
supporting the springs
26
a
and
26
b
, and connecting terminals
28
extending from the supporting members
27
a
and
27
b
. One end of each connecting terminal
28
passes through each slit
24
b
formed in the bottom of the main body
24
so as to extend outside the case
21
.
In the metal terminals
23
a
and
23
b
, the springs
26
a
and
26
b
are supported by the two supporting members
27
a
and
27
b
disposed at each side, as shown in FIG.
7
.
Additionally, the metal terminals
23
a
and
23
b
have the following arrangements:
(1) The supporting members
27
a
and
27
b
securely support the springs
26
a
and
26
b
so that the springs
26
a
and
26
b
can securely support the positive temperature coefficient thermistor element
22
interposed therebetween.
(2) Widths W
1
and W
2
of the springs
26
a
and
26
b
are set appropriately and a total value of widths W
3
and W
4
of the supporting members
27
a
and
27
b
is larger than a total value of the widths W
1
and W
2
of the springs
26
a
and
26
b
. With this arrangement, the springs
26
a
and
26
b
can have necessary spring thrusting forces and portions of the springs
26
a
and
26
b
in contact with the positive temperature coefficient thermistor element
22
have sufficient current capacity.
In this case, the widths W
1
and W
2
of the springs
26
a
and
26
b
are 1.5 mm and the widths W
3
and W
4
of the supporting members
27
a
and
27
b
are 1.9 mm.
When the total value of the widths W
3
and W
4
of the supporting members
27
a
and
27
b
is smaller than the total value of the widths W
1
and W
2
of the springs
26
a
and
26
b
, the supporting members
27
a
and
27
b
are deformed near the base ends of the springs due to the thrusting forces of the springs
26
a
and
26
b
. Consequently, satisfactory spring characteristics cannot be obtained. In addition, when the widths W
1
and W
2
of the springs
26
a
and
26
b
are too narrow, it is impossible to obtain both the necessary spring thrusting force and the current capacity of the portions of the springs
26
a
and
26
in contact with the positive temperature coefficient thermistor element
22
.
Recently, there has been a growing demand for cost reduction in electric apparatuses. With this tendency, there has also been a strong demand for cost reduction in demagnetizing positive temperature coefficient thermistors used in electric apparatuses such as color television sets. In order to meet these demands, the sizes of metal terminals defining positive temperature coefficient thermistors and the cost thereof need to be reduced. However, for the reasons described above, it is difficult to miniaturize the metal terminals, with the result that cost reduction in such a positive temperature coefficient thermistor cannot be sufficiently achieved.
As another example of the related art,
FIG. 8
shows a positive temperature coefficient thermistor of the three-terminal type, which includes two positive temperature coefficient thermistor elements
22
a
and
22
b
and a planar terminal
29
disposed therebetween. The positive temperature coefficient thermistor has the same problems as those shown in the positive temperature coefficient thermistor of the two-terminal type described above. In
FIG. 8
, elements having the same reference numerals as those used in
FIGS. 6 and 7
represent the same or equivalent parts shown in
FIGS. 6 and 7
.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a highly compact and very inexpensive positive temperature coefficient thermistor including miniaturized metal terminals while maintaining the characteristics and reliability of the device.
According to one preferred embodiment of the present invention, a positive temperature coefficient thermistor includes a positive temperature coefficient thermistor element, a case including a main body having an open top portion and construct to house the positive temperature coefficient thermistor element and a cover member arranged to cover the open top portion of the main body, and at least one pair of metal terminals including springs downwardly extending from connecting portions at the upper ends of the springs to be kept in contact with the positive temperature coefficient thermistor element by spring thrusting forces so as to obtain electrical continuity to the element and supporting the positive temperature coefficient thermistor element interposed between the springs to retain the positive temperature coefficient thermistor element inside the case, supporting members having upper ends that are integrated with the connecting portions to support the springs, and connecting terminals arranged to extend through slits provided in the bottom of the case and so as to extend outside the case. In this positive temperature coefficient thermistor according to this preferred embodiment, a total width value of the supporting members is preferably smaller than a total width value of the springs and the connecting portions at the upper ends of the springs engage with one of the main body and the cover member so that the connecting portions are retained at predetermined positions.
As described above, the metal terminals have the springs supporting the positive temperature coefficient thermistor element interposed therebetween, at least one supporting member supporting each of the springs, and the connecting terminals passing through the slits formed in the bottom of the main body of the case so as to extend outside the case. Additionally, the total width value of the supporting members is preferably smaller than the total width value of the springs. Additionally, the connecting portions at the upper ends of the metal terminals engage with the main body or the cover member to be retained at the predetermined positions. With this arrangement, deformation of the supporting members is reliably prevented. Thus, the metal terminals can be miniaturized without sacrificing the reliability required when retaining the positive temperature coefficient thermistor element and the reliability of electrical continuity to the positive temperature coefficient thermistor element. As a result, the entire positive temperature coefficient thermistor can be produced at much lower cost.
In other words, in the positive temperature coefficient thermistor according to preferred embodiments of the present invention, the connecting portions at the upper ends of the metal terminals engage with the main body or the cover member to be retained at predetermined positions. Accordingly, even when the metal terminals are miniaturized by setting the widths of the supporting members to b

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