Electricity: electrical systems and devices – Safety and protection of systems and devices – Transient responsive
Reexamination Certificate
2000-08-28
2003-10-21
Berhane, Adolf D. (Department: 2838)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Transient responsive
C361S119000
Reexamination Certificate
active
06636404
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to overvoltage and overcurrent protection apparatus for telecommunication circuitry and method of manufacturing same. In particular, the invention relates to fuses and thyristors.
Circuitry, particularly sensitive circuitry such as that found in telecommunication systems, require protection against both overcurrent and overvoltage conditions that may arise. Conditions such as short circuits may arise requiring an overcurrent protection device, such as a fuse, in order to prevent damage to circuitry.
Lightning is a common source of overvoltage in communication systems. Typically, communication systems consist of conductors in shielded cables suspended on poles or buried in the earth. The cable is made up of many conductors arranged in twisted pairs, commonly known as “Tip” and “Ring” lines for telephone systems, in particular. These cables are susceptible to transient energy from lightning and may conduct energy from the lightning to either a central office or subscriber equipment. Additionally, power sources for telecommunication systems are usually obtained from commercial power lines, which are also subject to excess energy from lightning that can, in turn, induce overvoltages in the telecommunication system being supplied by the power line.
Common approaches in the art to mitigate overcurrents and overvoltages include a combination of a fuse and a semiconductor overvoltage device such as a bi-directional thyristor, as shown in the circuit of
FIG. 1. A
fuse
100
is placed in series with a copper twisted pair
102
either in the Tip line
104
or in the Ring line
106
. Hence, the fuse
100
protects the tip and ring wiring and also a bi-directional thyristor
110
from excessive energy in the event a continuous overvoltage is coupled to the wiring, as might occur if a power line falls across the wiring.
In order to limit overvoltage conditions, an overvoltage device such as the bi-directional thyristor
110
is connected across the twisted pair
102
in parallel with the telecommunication system
108
. The thyristor
110
provides bi-directional “crow-bar” clamping of transients that may occur for either polarity. In particular, the thyristor
110
has a breakdown voltage at which a transient voltage exceeding this value will cause the thyristor
110
to begin clamping action across the lines
104
and
106
. As the transient voltage attempts to rise higher, the current through the thyristor
110
will increase until a break-over voltage is reached. At this point, thyristor action is triggered and the thyristor
110
switches to its “on” or “latched” state. This is a very low impedance state that shunts or “crow-bars” the line, thereby suppressing the magnitude of the transient voltage. When the transient voltage diminishes, the thyristor
110
turns off and reverts to a high impedance “off” state.
The circuit of
FIG. 1
is commonly used to protect “Tip” and “Ring” connections such as modems, telephones, facsimile machines, and line cards. While the circuit of
FIG. 1
is appropriate for copper twisted pair environments, other voltage environments are also suitable for circuits sought to be protected such as alarm circuits, power supplies, remote sensors, CATV, data lines, etc.
The protection circuits used in telecommunication applications, such as that shown in
FIG. 1
, commonly utilize discretely packaged fuse and thyristor components connected in printed circuit wiring. The discrete component approach, however, requires that the components be properly coordinated and matched with one another in order to meet pertinent regulatory and safety agency requirements. Also, the discretely packaged components are typically sourced separately, thus adding increased cost to the final product. Furthermore, using discrete components consumes considerable physical space on a printed circuit board since two separate component packages must be placed on the printed circuit board.
SUMMARY OF THE INVENTION
There is a need for an improved circuit device that achieves both overcurrent and overvoltage protection in a discrete integral package to more easily assure coordination and matching of the overcurrent and overvoltage devices. In addition, there is a need for a discrete integral package approach that affords lower final product cost and reduces the physical space consumed in a printed circuit.
These and other advantages are provided by the present invention, where overcurrent and overvoltage protection devices are packaged in a common housing to form a single discrete circuit element that is substantially no larger than one of the overcurrent or overvoltage devices that are each discretely packaged as previously known in the art, such as a standard surface mount telecommunications fuse, for example.
In an embodiment, the present invention provides an integral circuit protection device providing overcurrent and overvoltage protection for a circuit that is configured to be connected to the circuit. The device includes an overcurrent protection portion, an overvoltage protection portion, and a plurality of terminals for connecting both the overvoltage and overcurrent protection portions of the integral circuit device to the circuit to be protected. Incorporation of both overvoltage and overcurrent devices into a single housing assures that these components are coordinated and matched for a particular application, lowers the total cost of the device since the components are not sourced separately and allows for smaller size by incorporating the devices into the same package.
In another embodiment the plurality of terminals includes first, second and third terminals with the overcurrent protection portion electrically connected between the first and second terminals and the overvoltage protection portion connected between the second and third terminals.
In another embodiment, the overcurrent protection portion includes a fuse.
In another embodiment, the overvoltage protection portion includes a bi-directional thyristor.
In another embodiment, the plurality of terminals of the integral circuit are configured to electrically connect the overcurrent protection portion in series with the circuit to be protected and to electrically connect the overvoltage protection portion in parallel with the circuit to be protected when the integral circuit device is electrically connected to the circuit to be protected.
In yet another embodiment, the integral circuit further includes a thermally conductive portion that conducts heat away from the overvoltage protection portion.
In an embodiment, thermal coefficients of the thermally conductive portion and overvoltage protection portion are substantially the same.
In an embodiment, the overvoltage protection portion is at least partially encapsulated with an atmospherically resistant material.
In another embodiment, the integral circuit device is configured for mounting on a printed circuit board.
In another embodiment, the integral circuit device is configured substantially the same as a standard telecommunications fuse configuration.
In yet another embodiment of the present invention, a circuit element is provided for overvoltage and overcurrent protection of a circuit. The circuit element includes a circuit element housing having first, second and third terminals. An overcurrent protection device is electrically connected between the first and second terminals and contained by the circuit element housing. In addition, an overvoltage protection device is electrically connected between the second and third terminals and also contained by the circuit element housing.
In an embodiment, the circuit element housing is comprised of a tube having an outer surface, an inner hollow portion, a first end and a second end. The overcurrent protection device is disposed within the inner hollow portion of the tube, the overvoltage protection device and the second terminal are disposed on the outer surface of the tube, the first terminal is disposed at the first end and the second terminal is disposed at the se
Davidson Scott
Whitney Stephen J.
Zhang David
Bell Boyd & Lloyd LLC
Berhane Adolf D.
Littelfuse Inc.
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