Telephonic communications – Subscriber line or transmission line interface – Protective circuit
Reexamination Certificate
1999-09-14
2001-10-02
Isen, Forester W. (Department: 2644)
Telephonic communications
Subscriber line or transmission line interface
Protective circuit
C379S399010
Reexamination Certificate
active
06298134
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the protection of telecommunications equipment from voltage transients.
BACKGROUND OF THE INVENTION
Voltage transients may be produced in electrical circuits by a variety of things, such as lightning, AC power line induction or contact, electrostatic discharge or pulses generated by operation of electrical equipment. These phenomena can generate large currents on cables, telecommunications equipment, aircraft, and ships. Voltage transients can also penetrate and damage electrical systems, causing hardware damage or loss of stored data. Thus, voltage transients represent a threat to electrical/electronic equipment, especially in telecommunications equipment.
Various circuits and systems have been used for protecting telecommunications equipment from voltage transients. For example, circuits used with PBX out-of-building lines, special service lines such as carrier, pair-gain, and high speed data, and dedicated voice-band services such as pay phones and traffic-control communication lines have been designed to reduce damage caused by voltage transients. Conventional circuits utilize gas discharge tubes, transient voltage suppression thyristors, resistors, capacitors, inductors, avalanche diodes, and metal oxide varistors, to clamp transient voltages at prescribed potentials. These circuits may include a filter circuit comprising RC, RL or RLC circuits that are used to cutoff a prescribed range of frequencies. Sometimes the filtering is intentional, and sometimes it is not. Moreover, in order to have an effective filter circuit, the circuit designer must ensure that the resistance, capacitance and/or inductance values are maintained in a prescribed ratio. However, finding and maintaining a suitable “prescribed ratio” is no small task. In addition, the use of capacitors and inductors in a circuit or system can have a negative impact in terms of performance. For example, the saturation tendency of an inductor reduces its usefulness during impulse surges, especially at higher currents and slower risetimes. Nonetheless, conventional circuits have not considered eliminating capacitors, inductors and filtering from the overall design.
In light of the foregoing, there is a need for a system that protects telecommunications equipment from voltage transients as effectively as those heretofore developed, but which does not include capacitors, inductors and filtering.
SUMMARY OF THE INVENTION
The present invention is a system which substantially obviates one or more of the disadvantages of the conventional circuits.
An advantage of the present invention is that it provides an improved system for protecting telecommunications equipment from voltage transients with the elimination of filtering.
Another advantage of the present invention is that it provides a simple system that protects telecommunications equipment from voltage transients.
Another advantage of the present invention is that it improves voltage-limiting at slower impulse risetimes.
Another advantage of the present invention is that it manages developed, transversal voltage transients.
Another advantage of the present invention is that it increases the overall bandwidth of a system that protects telecommunications equipment from voltage transients.
Yet another advantage of the present invention is that it overcomes the system and component failure problems associated with capacitors and inductors.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the system particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described, the invention includes a high-energy foldback device between the current-carrying lines of a telephone system and ground; a voltage clamping device between the current-carrying lines; a foldback device between the current-carrying lines and ground; a first overcurrent protection device connected in series with the above foldback device; and a second overcurrent protection device in the lines between the high-energy foldback device and the above mentioned serially connected foldback device and first overcurrent protection device.
It is understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification. The drawings illustrate two embodiments of the invention and together with the description serve to explain the principles of the invention.
REFERENCES:
patent: 5953194 (1999-09-01), Atkins
patent: 6188557 (2001-02-01), Chaudhry
patent: 0 393 333 A (1990-10-01), None
patent: 2 267 789 A (1993-12-01), None
patent: WO 97 07580 (1997-02-01), None
Bell Michael J.
Harold Jefferey F.
Howrey Simons Arnold & White
Isen Forester W.
Tyco Electronics Corporation
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