Circuit design for data/telephone tip/ring pair surge...

Details Circuit design for data/telephone tip/ring pair surge... Circuit design for data/telephone tip/ring pair surge...

1999-10-28

2002-04-23

Huynh, Kim (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

High voltage dissipation

C361S124000

Reexamination Certificate

active

06377435

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to surge protection. More specifically, this invention relates to improved surge protection for tip and ring pair lines in telephone and data devices.
BACKGROUND OF THE INVENTION
Communications equipment, e.g., telephones, fax machines and computers, is commonly connected to telephone lines or similar data transmitting lines, such that a pair of lines, known as the “tip and ring pair,” exists between the equipment terminals and other terminals on a transmission line. Certain surge protection devices are commonly placed on the tip and ring lines in order to protect the connected equipment from unwanted surges in electrical energy. These devices usually provide overvoltage and/or overcurrent protection. For these surge protection devices, Underwriters Laboratory sets certain requirements, such as UL497/497A.
Despite the advantages of overcurrent and overvoltage devices, it has long been known that sneak currents (relatively low current and voltage) can penetrate existing protector designs and cause considerable damage to equipment circuit cards. In satisfaction of the UL497 and 497A standards, current designs of communications surge protectors utilize overcurrent devices incapable of mitigating the affects of sneak currents. These devices include fuses and relatively high voltage PTCs (Positive Temperature Coefficient Thermistors). Overvoltage clamping devices may also be included in such devices. The operation of such overvoltage clamping devices will be understood by those skilled in the art.
Since the fuses and high voltage PTC protection circuits commonly used to meet UL overcurrent requirements are too slow too mitigate sneak currents, an object of the invention is an improved circuit design that both meets UL requirements and provides effective sneak current protection.
SUMMARY OF THE INVENTION
The present invention in one embodiment is a circuit for protection of data and telephone tip/ring pair lines. The circuit includes tip and ring lines, each having a protected side and an unprotected side; first and second overcurrent devices connected in series with the unprotected side of the tip and ring lines line; a grounded over-voltage clamping device connected to both the tip line and the ring line at a point intermediate the protected side and the unprotected side, the clamping device being connected to ground; and first and polymer PTC elements connected, respectively, in series with the protected side of the tip and ring lines.


REFERENCES:
patent: 4903295 (1990-02-01), Shannon et al.
patent: 5555153 (1996-09-01), Frederiksen et al.
patent: 5909349 (1999-06-01), Brower et al.
patent: 6031706 (2000-02-01), Nabell
patent: 6040972 (2000-03-01), Takeuchi

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