U.S. patent application number 09/842925 was filed with the patent office on 2001-08-23 for low profile mount for plural lower electrode metal oxide varistor package and method.
This patent application is currently assigned to Harris Ireland Development Company Ltd.. Invention is credited to McLoughlin, Neil.
Application Number | 20010015685 09/842925 |
Document ID | / |
Family ID | 23588000 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010015685 |
Kind Code |
A1 |
McLoughlin, Neil |
August 23, 2001 |
Low profile mount for plural lower electrode metal oxide varistor
package and method
Abstract
A low profile mount for a disc varistor. A thermally sensitive
switch is provided both for single and multiple electrode
embodiments. The switch may be placed in a shorting circuit and
include a spring biased conductor prevented from closure by a heat
sensitive element which softens in responsive to excessive heat.
The varistor may be fused to prevent excessive current from a short
circuited but not open circuited varistor. Methods are also
provided.
Inventors: |
McLoughlin, Neil;
(Blackrock, IE) |
Correspondence
Address: |
L. Lawton Rogers, III
Suite 300
1401 Eye Street, N.W.
Washington
DC
20005
US
|
Assignee: |
Harris Ireland Development Company
Ltd.
|
Family ID: |
23588000 |
Appl. No.: |
09/842925 |
Filed: |
April 27, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09842925 |
Apr 27, 2001 |
|
|
|
09401497 |
Sep 22, 1999 |
|
|
|
Current U.S.
Class: |
338/20 ;
338/21 |
Current CPC
Class: |
H01C 7/126 20130101;
H05K 3/301 20130101 |
Class at
Publication: |
338/20 ;
338/21 |
International
Class: |
H01C 007/10 |
Claims
What is claimed is:
1. A low profile mount for a disc varistor comprising: an
insulative base having a circular receptacle for a varistor disc;
an exposed bottom electrical contact in said receptacle in position
to contact an electrode on the bottom flat side of a varistor disc
when placed in said receptacle; and an upper electrode extending
upwardly from an said base outside of said receptacle and being
downwardly biased toward said base over said receptacle in position
to contact the electrode on the bottom flat side of a varistor disc
when placed in said receptacle.
2. The mount of claim 1 wherein said upper electrode is a
conductive metal spring.
3. The mount of claim 1 wherein the low profile device is surface
mounted on a printed circuit board.
4. The mount of claim 1 wherein the low profile device is through
hole mounted on a printed circuit board.
5. The mount of claim 1 wherein the disc varistor is 14-20 mm in
diameter.
6. The mount of claim 1 wherein the disc varistor is 7-45 mm in
diameter.
7. The mount of claim 1 wherein the low profile device is coated
with a moisture barrier.
8. The mount of claim 1 including a shorting electrode upwardly
extending from said base outside of said receptacle and being
downwardly biased towards said base over said receptacle in
position to contact the electrode on the upper flat side of a
varistor disc when placed in said receptacle, said shorting
electrode being electrically connected to said bottom electrode;
and an insulator intermediate said shorting electrode and the upper
electrode of a varistor disc when placed in said receptacle in
position to prevent contact between the shorting electrode and the
upper electrode, said insulator being thermally reactive to permit
contact between said shorting electrode and the upper electrode of
a varistor disc under the bias of said shorting electrode whereby
the elevation in the temperature of a varistor disc in said
receptacle causes said insulator to react to short the electrodes
of the varistor disc.
9. The mount of claim 8 wherein said shorting disc is a metal
spring.
10. The mount of claim 8 wherein said shorting disc is magnetically
biased.
11. The mount of claim 8 wherein said insulator melts at
temperatures above a predetermined value.
12. The mount of claim 8 wherein the insulator deteriorates between
150-200.degree. C.
13. The mount of claim 8 wherein the insulator deteriorates at
163.degree. C.
14. The mount of claim 8 wherein the insulator consists essentially
of benzanilide.
15. The mount of claim 1 including at least one additional upper
electrode extending upwardly from an said base outside of said
receptacle and being downwardly biased toward said base over said
receptacle in position to contact an electrode on the top flat side
of a varistor disc when placed in said receptacle, said upper
electrodes being spaced apart to thereby be positioned to contact
different upper electrodes on a segmented varistor disc.
16. The mount of claim 1 including at least one additional exposed
bottom electrical contact in said receptacle in position to contact
an electrode on the bottom flat side of a segmented varistor disc
when placed in said receptacle.
17. A mount for an electrical component having exposed upper and
lower electrodes comprising: a insulative body with an upwardly
open receptacle adapted to receive an electrical component; a lower
contact carried by said body within said receptacle in position to
contact the lower electrode of a component when received therein:
an upper contact carried by said body above said receptacle in
position to contact the upper electrode of the component when
received therein, said upper contact being downwardly biased toward
said receptacle.
18. The mount of claim 17 including a second upper contact carried
by said body above said receptacle in position to contact a second
upper electrode of the component when received therein, said second
upper contact being downwardly biased toward said receptacle.
19. The mount of claim 18 wherein said second upper contact is
electrically connected to said lower electrical contact; and
including a thermally responsive insulator between said second
upper contact and the upper electrode of the electrical component
for preventing contact therebetween under predetermined thermal
conditions within the component, said insulator being responsive to
a predetermined thermal condition within the component to permit
contact between said second contact and the upper electrode of the
component.
20. The mount of claim 19 wherein the insulator consists
essentially of benzanilide and wherein the insulator deteriorates
between 150-200.degree. C.
21. The mount of claim 19 wherein the insulator deteriorates at
163.degree. C.
22. The mount of claim 18 wherein said second upper contact is
electrically isolated from both said lower contact and said first
mentioned upper contact to thereby adapt said mount for use with
components with segmented upper electrodes.
23. A mount for an electrical component having an exposed lower
electrode and a plurality of exposed upper electrodes comprising: a
insulative body with an upwardly open receptacle adapted to receive
an electrical component; a lower contact carried by said body
within said receptacle in position to contact the lower electrode
of a component when received therein: a plurality of spaced upper
contacts carried by said body above said receptacle in position to
contact spaced upper electrodes of the component when received
therein, each of said plurality of upper contacts being downwardly
biased toward said receptacle.
24. The mount of claim 23 wherein said plurality is four.
25. The mount of claim 24 wherein said component is a varistor.
26. A mount for an electrical component having an exposed upper
electrode and a plurality of exposed lower electrodes comprising: a
insulative body with an upwardly open receptacle adapted to receive
an electrical component; a plurality of spaced lower contacts
carried by said body within said receptacle, each of said lower
contacts being in position to contact one of the segmented lower
electrodes of a component when received therein: an upper contacts
carried by said body above said receptacle in position to contact
the upper electrodes of the component when received therein, said
upper contacts being downwardly biased toward said receptacle.
27. The mount of claim 26 wherein said component is a varistor.
28. The mount of claim 27 wherein said plurality is four.
29. A method of mounting an electrical component having exposed
upper and lower electrodes on a printed circuit board comprising
the steps of: (a) providing an insulative body having an upwardly
open receptacle adapted to receive an electrical component; (b)
positioning a lower contact within the receptacle in the body in
position to contact the lower electrode of a component when
received therein: (c) providing an upper contact carried by the
body above the receptacle in the body in position to contact the
upper electrode of the component when received therein; (d)
downwardly biased the upper contact toward the receptacle in the
body, so that an electrical component when received within the
receptacle in the body will electrically contact the lower contact
within the receptacle and be contacted by the upper contact under
the downward bias thereof.
30. The method of claim 29 wherein the component is a varistor.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a surface mount for an electrical
component and more particularly to a surface mount for a metal
oxide varistor.
[0002] Surface mounting of components on printed circuit boards is
common and it is desirable that the mounts be low in profile so
that the distance between boards can be minimized and the size of
the electronic chassis thus reduced. Where the electrical component
is a thin element such as a disc with electrodes on both flat
sides, low profile mounts are particularly desirable.
[0003] It is also desirable that the number of components required
for mounting be minimized because of the area on the circuit board
each component occupies. Thus it is highly desirable that the mount
be compatible with components having multiple electrodes.
[0004] The thermal characteristics of the electrical components is
generally a concern and it is desirable that the surface mount be
compatible with, or integrated with one or more thermally sensitive
switches. The thermal characteristics for many electrical circuit
components such as varistors are particularly important where the
component is coated with epoxy. In the event of a sustained
overvoltage condition across the component, the current through the
component can cause the temperature to increase sufficiently to
cause the epoxy coating to smoke or ignite. Similarly, the epoxy
coating can smoke or ignite in the event the component is subjected
to a significant current pulse such that the component internally
shorts but does not destruct, i.e., does not open-circuit.
[0005] The current solution to this overheating problem is to wire
in series with the component a thermal cutout device in
sufficiently close physical proximity to respond to the heat in the
component to short circuit and thereby disconnect the component.
This solution requires the addition of extra components and
increases the cost and complexity of the circuit. Since great care
must be taken to keep the thermal cutout device in close physical
proximity to the component to preserve the responsiveness without
overreacting, interference may occur with any surface mount.
[0006] Additionally, the "thermal connection" between the component
and the thermal cutout device may be difficult to optimize in a
surface mount.
[0007] Finally, low temperature thermal cutout devices may not be
able to survive the soldering operation required to attach the
component to a printed circuit board or the like, and a surface
mount to which the component may be mounted without soldering is
highly desirable.
[0008] Many of the above problems are exacerbated where the
electrical component is a disc varistor. Disc varistors are well
known and generally comprise a thin disc of a metal oxide or other
voltage variable resistive material with an electrode on opposite
flat sides of the varistor material. Known surface mounts for the
smaller sizes, e.g., 7-10 mm, generally include a molded plastic
body into which spring electrodes exiting the sides of the body are
internally exposed in position to be contacted by the electrodes of
the disc varistor when inserted therebetween from the front of the
body.
[0009] One example of such prior art mount is illustrated in FIGS.
1 and 2 where the disc varistor 18 comprises a disc of varistor
material 20 with surface electrodes 22 and 24 on the flat sides
thereof. The varistor 18 may be inserted into the front opening of
a plastic body 26 which carries a top contact 28 and a bottom
contact 30 conveniently spring biased toward each other and
separated by the insertion of the disc varistor. The ends of the
contacts 32, 34 may be used to electrically connect the circuit to
other components on the printed circuit board on which the body 26
may be mounted. Such mounts are expensive to manufacture and are
generally higher in profile than desired. Moreover, they do not
provide for multiple electrodes, for temperature protection or for
a fuse.
[0010] Accordingly, it is an object of the present invention to
obviate many of the above problems and to provide a novel surface
mount and method for an electrical component on a printed circuit
board.
[0011] It is another object of the present invention to provide a
novel surface mount and method in which the mount is low
profile.
[0012] It is still another object of the present invention to
provide a novel surface mount and method in which the component may
be connected without soldering.
[0013] It is yet another object of the present invention to provide
a novel surface mount and method which is readily adapted for
multiple electrical connections.
[0014] It is yet still another object of the present invention to
provide a novel surface mount and method which is compatible with a
thermal switch.
[0015] It is a further object of the present invention to provide a
novel surface mount which is inexpensive and simple in
construction.
[0016] It is yet a further object of the present invention to
provide a novel surface mount and method which short circuit
protection is available.
[0017] It is still a further object of the present invention to
provide a novel surface mount and method in which the mount may be
coated with a moisture barrier and/or have edge passivation.
[0018] These and many other objects and advantages of the present
invention will be readily apparent to one skilled in the art to
which the invention pertains from a perusal of the claims, the
appended drawings, and the following detailed description of the
preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a pictorial view of a prior art surface mount
package for a varistor disc.
[0020] FIG. 2 is a section in elevation taken through lines 2-2 of
FIG. 1.
[0021] FIG. 3 is a side view in elevation of one embodiment of the
surface mount of the present invention.
[0022] FIG. 3A is an exploded pictorial view of the mount of FIG.
3.
[0023] FIG. 4 is a side view in elevation of a second embodiment of
the surface mount of the present invention.
[0024] FIG. 5 is a side view in elevation of the embodiment of FIG.
4 with a thermal switch in the open position.
[0025] FIG. 6 is a schematic circuit diagram of the varistor and
switch of FIGS. 3 and 4 with a fuse in series with the
varistor.
[0026] FIG. 7 a side view in elevation of a third embodiment of the
surface mount of the present invention adapted for two electrodes
on the upper surface of the varistor.
[0027] FIG. 8 is a top plan view of a two component electrode
compatible with the mount of FIG. 7.
[0028] FIG. 9 is a schematic circuit diagram of the varistor of
FIG. 8.
[0029] FIG. 10 is a side view in elevation of a fourth embodiment
of the surface mount of the present invention adapted for two
electrodes on the lower surface of the varistor.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0030] With reference to FIGS. 3 and 3A, a preferred embodiment of
the mount of the present invention includes a molded plastic body
36 with a central circular depression dimensioned to receive a disc
varistor 18 (varistor material 20 and electrodes 22 and 24) to a
depth of about one-half the thickness thereof. Centrally located
within the depression is a second depression adapted to receive a
circular contact 38 which exits the body 36 to provide a first lead
40. The contact 38 desirably extends upwardly above the bottom of
the first depression in order to insure contact with the bottom
electrode 24 of the varistor 18.
[0031] The body 38 is desirably molded with a support 42 for the
second contact 44 which may be made from an electrically conductive
spring wire so that it is spring biased downwardly into contact
with the upper electrode 22 of the disc varistor 18. The contact
extends through the support 42 to provide a second electrical lead
46 of the mount.
[0032] As shown in FIG. 4, the leads 40 and 46 may extend
downwardly so as to penetrate through a printed circuit board for
electrical connection to an electrical circuit on the lower side
thereof.
[0033] As described more fully in applicant's copending application
Ser. No. filed concurrently herewith for "Thermally Protected Metal
Oxide Varistor And Method", the disclosure of which is hereby
incorporated herein by reference, thermal protection may be
provided by a third contact 50 which may be constructed in the same
manner as the contact 44 to provide a third lead 52, but which
includes a thermal element 54 covering at least a portion of the
contact 50 to prevent contact with the upper electrode 22 of the
varistor 18. The thermal element 54 may be any suitable
conventional insulator responsive to excessive heat in the varistor
to either physically dissipate or to lose its insulative
characteristics. An example of such a thermally reactive insulator
is benzanilide. Benzanilide is generally rigid up to its melting
temperature, which is generally in the range of 150-200.degree. C.
and is preferentially 163.degree. C. Benzanilide adheres well and
breaks down at its melting temperature to a viscosity that is
water-like. It has been found desirable for the body 36 to include
a second support 56 at the end of the mount opposite to the support
42 to lend rigidity to the contact 50.
[0034] The circuit including the third contact 50 is shown in FIG.
6 where a shorting circuit is shown with the leads 52 and 40
electrically connected. Under normal operating conditions, current
flows through the varistor 18 via the leads 40 and 46. An
undesirable thermal condition in the varistor 18 caused by a
excessive current through the varistor from a sustained overvoltage
condition across the varistor, or by a high current pulse through
the varistor which causes an internal short in the varistor but
does not cause the varistor to destruct, i.e., to open circuit. In
the event of such an undesirable thermal, the effective
disappearance of the insulating means 54 in response thereto
permits contact between the electrode 50 and the upper electrode 22
of the varistor and effects a short circuit across the varistor
18.
[0035] While the spring wire contact has been found desirable, it
is to be noted that other biasing means may be adequate, e.g., a
discrete spring for the electrical contact or a magnet. The shape
of the varistor is not a part of this invention, and it may be
square or other forms as desired so long as the depression in the
body of the mount is compatible.
[0036] However, the mount of the present invention finds particular
utility where the disc varistor electrodes are segmented as shown,
e.g., in FIG. 8. With reference to FIG. 8, one of the electrodes,
e.g.,the upper electrode 22, may be segmented into two, three or
four parts, each forming a varistor element with the single lower
electrode 24.
[0037] As shown in FIG. 7, an embodiment with two segments on the
upper electrode may use two spring wire contacts 60, 62 connected
respectively to leads 64, 66 to form the circuit shown in FIG. 9.
As shown in FIG. 10, the identical circuit may be formed using the
two segment varistor of FIG. 8 with the segmented electrode facing
downwardly and a single contact 44 in contact with the single, now
upper, electrode 24. This embodiment requires that the body 36
include not one central contact 38 as illustrated in FIG. 3A, but
two spaced contacts 38A and 38B as shown in FIG. 10.
[0038] While preferred embodiments of the present invention have
been described, it is to be understood that the embodiments
described are illustrative only and that the scope of the invention
is to be defined solely by the appended claims when accorded a full
range of equivalence, many variations and modifications naturally
occurring to those of skill in the art from a perusal hereof.
* * * * *