WO2002033797A1

WO2002033797A1 - Failsafe mechanism for telecommunications protector module

Info

Publication number: WO2002033797A1
Application number: PCT/US2001/032477
Authority: WO
Inventors: David L. Rawlings
Original assignee: Porta Systems Corporation
Priority date: 2000-10-19
Filing date: 2001-10-17
Publication date: 2002-04-25
Also published as: AU2002213354A1

Abstract

A failsafe mechanism for protecting telecommunication equipment, having a tip (26) and ring (28), by shunting a sustained overvoltage or excessive current surge to ground, includes a failsafe clip (36), a diode bridge (11), and a trigger unit (12). The trigger unit is configured to bias the second end of the failsafe clip in the normally open position, but releases the failsafe clip when either the sustained overvoltage causes the module components to become excessively hot, or the current surge is high enough to cause a fusible link (34) to part, whereby the failsafe clip shunts all current to the ground.

Description

FAILSAFE MECHANISM FOR TELECOMMUNICATIONS

PROTECTOR MODULE

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates in general to telecommunication line protection equipment, and more particularly to overvoltage/overcurrent circuits and apparatus for protecting telephone lines.

Description of the Prior Art

The transmission of information over the national telecommunications network involves the use of standard telephone subscriber lines and the like. One or more telephone lines extend from centralized switching systems directly to the respective telephone set, computer, answering machine, etc. in the subscriber's home, office or building. As such, that portion of the telephone line that extends outside of a building structure is exposed to the environment. Because of this environmental exposure, there exists the possibility that aerial telephone lines can be either struck by lightning or crossed with power transmission lines. Buried telephone lines can also be subjected to hazardous voltages due to excavation, trenching or digging, where equipment can cut through and cause short circuits between buried power lines and the telephone lines. It can be appreciated that overvoltage/overcurrents caused by lightning and power line crosses can cause catastrophic damage, not only to the telephone lines themselves, but also to the equipment connected to the telephone lines.

As a result of the foregoing hazardous conditions, specifications and standards have been established for telephone line protection devices and circuits so that if such lines come in contact with hazardous voltages, the likelihood of damage to electrical equipment connected thereto is substantially reduced. Indeed, the standard telephone line protection module includes five terminals or pins that are arranged in a particular configuration. One pair of pins is associated with the telephone tip conductor and another pair is associated with a telephone line ring conductor. The fifth terminal is connected to a ground bus. One or more overvoltage/overcurrent protection circuits or devices are responsive to hazardous voltages to connect either the tip or ring conductors, or both, to the ground terminal so that the apparatus connected to the telephone line is protected from exposure to the hazardous voltages or currents.

Telcordia Technologies, Inc. of Piscataway, New Jersey ("Telcordia") has established industry standards that are widely adopted in the telecommunications industry. In particular, standards for protector modules or units are set forth in

"Generic Requirements for Telecommunications Line Protector Units" publication number GR-974-CORE, Issue 2, December 1999, which is incorporated herein by reference. Chapters 4 and 7 set forth the electrical requirements that are required for most central office and outside plant applications today.

U.S. Pat. Nos. 5, 101 ,317; 5,341 ,270; and 5,359,657 are illustrative of conventional telephone line protection devices. In many of the telephone line protection devices, including those identified in the aforementioned patents, primary overvoltage protection is provided by fast-acting solid state devices, many of which are available from Teccor Electronics, Inc. of Irving, Tex. These solid state devices arc often referred to as SIDACtor.RTM. devices and are described more fully in U.S. Pat. No. 5,479,031. Fail-safe protection is often provided by other mechanical apparatus that is part of the telephone line protection module. The fail-safe apparatus is responsive to the thermal energy generated as a result of a sustained overvoltage condition imposed on the telephone line conductors as might occur in a power cross. This apparatus generally involves a material having a low-temperature melting point, such as a tin-lead solder which, when subjected to a temperature that causes melting thereof, enables a spring to force a conductor bar to move and short circuit the tip and ring line conductors to the ground terminal of the module. The melting point of the solder compounds generally used may be as low as 150 degree F. Low-temperature melting solders are desirable because they trigger the fail-safe mechanism before excess temperature within the protector module causes it to ignite. i United States Patent No. 6, 104,591 discloses a telephone line protection element constructed of three lead frames having contact fingers for holding therebetween a semiconductor cell providing overvoltage/overcurrent protection between the telephone line and the customer circuits. The lead frames are soldered to a resistive semiconductor material to provide a fail-safe mechanism that mechanically connects either the tip or ring telephone line conductors to ground if a sufficient overcurrent exists. In response to an overcurrent, the resistive semiconductor material generates heat and melts the solder in contact therewith, which allows a pre-bent member of the lead frame to move in contact with a ground terminal, thereby shunting the overcurrent to ground.

Figures 8A and 8B illustrate prior art overvoltage circuits that use more than one thyristor. The overvoltage circuit shown in Figure 8 A is illustrative of one used by Teccor Electronics, Inc. and uses three (3) thyristors 401. A problem associated with this design is that it is expensive to make because of the high cost of thyristors. In addition, the overvoltage function of the design is not balanced in accordance with Telcordia's Balanced Voltage Limiting requirements in chapter 7.1.1 because of a mismatch in the thyristors connected to the tip and ring. The overvoltage circuit shown in Figure 8B uses two (2) thyristors 402 and is illustrative of one offered by Texas Instruments. This design has similar problems with not being balanced and having a high cost.

Basic primary overvoltage protection and its associated fail-safe mechanism can be fabricated in a host of different variations, many of which are extremely complicated and thus expensive. Aside from the cost considerations of a mechanically complex device, the reliability is often compromised as a result of numerous mechanical and electrical components and interconnections. It can be appreciated that as the number of components increases and the component complexity increases, the assembly time and cost also increase.

Failsafe mechanisms, as stated previously, are needed to prevent overheating and possible ignition of protector modules. Without such mechanisms, this overheating might otherwise occur in the presence of sustained overvoltage of moderate magnitude as can result from a power line being crossed with a telecommunication circuit. The sustained overvoltage will gradually heat the protection components within the protector module and it is the purpose of the failsafe mechanism to relieve the subject components of this heating by conducting the offending voltages to ground before ignition occurs.

In addition to this category of failsafe action, there is another, entirely separate failsafe function associated with voltage/current surges that are in excess of the ability of solid state arrestor components to fail short. A typical thyristor overvoltage protector as is utilized in protector modules will respond to a 700A, 10/1000 μs waveshape surge by becoming an open circuit. Without the benefit of some auxiliary mechanism, downstream circuitry now lays unprotected against further surges. A suitable failsafe mechanism is therefor needed to conduct subsequent overvoltage surges to ground.

There are, thus, two separate and distinct requirements for a successful failsafe mechanism:

1. Short Tip and Ring to ground under conditions of sustained, moderate overvoltage which is causing the protector to constantly redirect such overvoltages to ground and thus become excessively hot.

2. Short Tip and Ring to ground under conditions wherein a surge enters the protector module with enough power to cause the solid state overvoltage device to fail open circuit.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and apparatus, which significantly reduces the cost of overvoltage/ failsafe circuits for telephone equipment.

It is a further object of the present invention to provide a method and apparatus, which protects telephone equipment from excessive voltages and/or currents normally occurring on telephone lines, which are caused by lightning strikes, power line crosses, and surges induced by adjacent power lines.

In accordance with the present invention, a failsafe mechanism for protecting telecommunication equipment, having a tip and ring, by shunting to ground either a sustained overvoltage or excessive current surge includes a failsafe clip, a diode bridge, and a trigger unit. The failsafe clip has a first end which is electrically coupled to ground and a second end that is normally biased in an open position with respect to the tip and ring of the telecommunication equipment in the absence of a sustained overvoltage or excessive current pulse. The diode bridge is electrically coupled to the tip and ring of the telecommunication equipment and the ground. The trigger unit is electrically coupled to the diode bridge and configured to bias the second end of the failsafe clip in the normally open position. The trigger unit is biased open under normal operating voltages and currents. The trigger unit releases the failsafe clip when either the sustained overvoltage causes the module components to become excessively hot, or the current surge is high enough to cause a fusible link to part whereby the failsafe clip shunts all induced current to ground.

In a preferred embodiment, the diode bridge preferably includes a first diode, a second diode, a third diode, and a fourth diode. Each of the diodes includes an anode and a cathode. Preferably the cathode of the first diode is coupled to the cathode of the second diode and defines a first node. Preferably the anode of the second diode is coupled to the cathode of the third diode and defines a second node. Preferably the anode of the third diode is coupled to the anode of the fourth diode and defines a third node. Preferably the cathode of the fourth diode is coupled to the anode of the first diode and defines a fourth node. Preferably the trigger unit is coupled between the second node and the first node. Preferably the failsafe mechanism also includes a fifth diode and a sixth diode each having an anode and a cathode. Preferably the cathode of the fifth diode is coupled to the trigger unit, and the anode of the fifth diode is coupled to the ground. Preferably the anode of the sixth diode is coupled to the trigger unit, and the cathode of the sixth diode is coupled to the ground. Preferably, the trigger unit includes a heat sensing diode, a thyristor and a fusible link electrically connected between the heat sensing diode and the thyristor. The fusible link biases the second end of the failsafe clip in the open position in the absence of sustained overvoltage and associated excessive heat or a current surge that might be high enough to cause a fail-open condition ofthe overvoltage component. This fusible link releases the second end of the failsafe clip upon the occurrence of either condition, whereby the failsafe clip shunts all induced current to ground. The fusible link is preferably a conductor wire electrically connecting the heat sensing diode and the thyristor. The conductor wire has a failure point at a known high current condition, whereby the conductor wire parts and releases said failsafe clip from its biased open position.

In a preferred embodiment, the trigger unit is disposed on a printed circuit board and the heat sensing diode is connected to the printed circuit board via a solder having a predetermined melting point. The solder releases the fusible link from the printed circuit board when a sustained overvoltage causes the heat sensing diode or the thyristor, which are soldered to the two ends ofthe fusible link to exceed the solder melt temperature, whereby the failsafe clip is released from its biased open position. Under a condition of very high current surge, typically more than 700A, 10/1000 μs waveshape, no solder melting occurs but the narrow fusible link section fuses open such that said failsafe clip is released from its biased open position.

Preferably, the failsafe clip further includes a central portion having a non- conductive finger making contact with the fusible link for biasing the failsafe clip in the open position. The second end of the failsafe clip preferably includes first and second legs being configured to respectively electrically communicate with the tip and ring of the telecommunication equipment when the failsafe clip is released from its biased open position. At least one of the tip and ring preferably includes a contact member for connecting with the respective first or second leg of the failsafe clip when the failsafe clip is released from its biased open position.

In a preferred embodiment, the first end of the failsafe clip is mounted on a first surface of the printed circuit board and the trigger unit is mounted on a second surface of the printed circuit board opposite the first surface. The printed circuit board has an opening extending between the first and second surfaces through which the finger of the failsafe clip engages the fusible link of the trigger unit to bias the failsafe clip in the open position.

In an alternative embodiment, the first end of the failsafe clip is not electrically coupled to ground. Nevertheless, the failsafe mechanism shunts a sustained overvoltage or very high current surge, typically more than 700A, 10/1000 μs waveshape to the ground. In this embodiment, the second end of the failsafe clip is normally biased in an open position with respect to the tip, the ring and ground of the telecommunication equipment in the absence of a sustained overvoltage or very high current surge, typically more than 700A, 10/1000 μs waveshape. The trigger unit releases the failsafe clip when either of these conditions occurs, whereby the failsafe clip shunts all current to ground.

In the alternative embodiment, the second end of the failsafe clip includes first, second and third legs being configured to respectively electrically communicate with the tip, the ring and ground of the telecommunication equipment when the failsafe clip is released from its biased open position. At least one of the tip, the ring and ground preferably includes a contact element for connection with the respective first, second or third leg of the failsafe clip when the failsafe clip is released from its biased open position.

These and other objects, features, and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention have been chosen for purposes of illustration and description and are shown in the accompanying drawings, wherein:

Figure 1 is a schematic diagram showing a failsafe circuit in accordance with a first embodiment of the present invention; Figure 2 is a schematic diagram showing a failsafe circuit in accordance with a second embodiment of the present invention;

Figure 3 is a top view plan of the first embodiment of a failsafe mechanism in accordance with the failsafe circuit shown in Figure 1 showing the failsafe clip in phantom;

Figure 4 is a side elevation view of the first embodiment of a failsafe mechanism showing a non-conductive finger of the failsafe clip biasing a fusible wire of a trigger unit;

Figure 5 is a cross sectional view showing a soldered connection of the fusible wire at the heat sensing diode;

Figure 6 is a side elevation view of the second embodiment of a failsafe mechanism in accordance with the failsafe circuit shown in Figure 2 showing a fusible wire restraining the failsafe clip;

Figure 7 is a top view plan of the second embodiment of a failsafe mechanism in accordance with the failsafe circuit shown in Figure 2;

Figure 8A is a prior art overvoltage protection circuit that uses three thyristors;

Figure 8B is a prior art overvoltage protection circuit that uses two thyristors;

Figure 9A is a bottom plan view of a third embodiment of a failsafe mechanism;

Figure 9B is a side elevation view of the third embodiment of the failsafe mechanism showing a finger of the failsafe clip biasing a fusible wire of a trigger unit; and

Figure 10 is a bottom plan view of an alternative embodiment of a failsafe mechanism. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Initially the similar features of two separate embodiments of the present invention shown in Figures 1 and 2 are briefly described to explain the electrical connectivity of the failsafe circuits 10 shown therein. Each failsafe circuit 10 has a diode bridge 1 1 , a trigger unit 12, and a failsafe clip 36. The trigger unit 12 generally includes a heat sensing diode 30, a thyristor 32, and a fusible link 34, but the details for each embodiment ofthe invention are different and are explained along with the failsafe clip 36 separately below. The diode bridge 1 1 preferably includes at least four diodes 14, 16, 18, 20. The cathode of diode 14 is preferably coupled to the cathode of diode 16 at node A, and the anode of diode 16 is preferably coupled to the cathode of diode 18 at node B of the diode bridge 1 1. The anode of diode 18 is preferably coupled to the anode of diode 20 at node C, and the cathode of diode 20 is preferably coupled to the anode of diode 14 at node D of the diode bridge 1 1.

The trigger unit 12 is preferably coupled between node A and node C. In addition, the failsafe circuit preferably includes diodes 22 and 24. The cathode of diode 22 is preferably coupled at node A, and the anode of diode 24 is preferably coupled at node C. Both the anode of diode 22 and the cathode of diode 24 are preferably coupled to ground.

The general operation of the failsafe circuit will now be described under various conditions. Generally, under normal conditions, the fusible link 34 will simply be a conductor connecting diode 30 and thyristor 32 unless the fusible link 34 has already failed resulting in the failsafe clip 36 shunting all current to ground as described in detail below. If a positive voltage that is higher than the trip voltage of the thyristor 32 appears from the tip terminal 26 (positive) to the ring terminal 28 (negative), then diodes 14, and 18 are biased on, and the voltage between the tip and ring terminals is reduced to near zero as the thyristor crowbars. If a positive voltage that is higher than the trip voltage of the thyristor 32 appears from the tip terminal 26 (positive) to ground, then diodes 14, and 24 are biased on, and the voltage between the tip terminal and ground is reduced to near zero as the thyristor crowbars. If a positive voltage that is higher than the trip voltage of the thyristor 32 appears from the ring terminal 26 (positive) to ground, then diodes 16, and 24 are biased on, and the voltage between the ring terminal and ground is reduced to near zero as the thyristor crowbars.

Similarly, if a negative voltage higher than the trip voltage of the thyristor 32 appears from the tip terminal 26 (negative) to the ring terminal 28 (positive), then diodes 16 and 20 are biased on, and the voltage between the tip and ring terminals is reduced to near zero as the thyristor crowbars. If a negative voltage higher than the trip voltage of the thyristor 32 appears from the tip terminal 26 (negative) to ground, then diodes 22 and 20 are biased on, and voltage between the tip terminal and ground is reduced to near zero as the thyristor crowbars. If a negative voltage higher than the trip voltage of the thyristor 32 appears from the ring terminal 28 (negative) to ground, then diodes 22 and 18 are biased on, and the voltage between the ring terminal and ground is reduced to near zero as the thyristor crowbars.

Further details concerning the operation of the diode bridge 1 1 can be found in V. Veley, "Benchtop Electronics Handbook", McGraw-Hill Book Company, pp. 288- 294, (1998), and G. Deboo and C. Burrous, "Integrated Circuits and Semiconductor Devices: Theory and Operation", McGraw-Hill Book Company, pp. 365-458, (1977), which are incorporated herein by reference.

Referring initially to Figures 1 and 2, the trigger unit 12 generally includes a heat sensing diode 30, a thyristor 32, and a fusible link 34. In both embodiments, the fusible link 34 is made from fusible wire configured to restrain the failsafe clip 36 from making an electrical connection between ground and the tip 26 and the ring 28 as shown in Figures 4 and 6 under normal operating conditions. Preferably the fusible wire is about 36 gauge which has been found to fail at certain high current pulses to comply with the requirements set forth in Telecordia's specifications. Preferably the fusible link is not insulated for fabrication purposes. The heat sensing diode 30 is preferably connected to a printed circuit board 38 with a solder having a melting point selected to release the heat sensing diode 30 from the printed circuit board 38 when it gets too hot due to an overvoltage condition. Although the fusible link 34 may not fail per se under this condition, the failsafe clip 36 will shunt the current to ground. Referring now to Figures 3 to 6, the failsafe mechanism 100, 200 in accordance with the present invention generally includes the diode bridge 1 1 (as shown in Figures 1 and 2), the trigger unit 12, and the failsafe clip 36. The details of the diode bridge 1 1 are discussed above with respect to failsafe circuit 10 shown in Figures 1 and 2. The failsafe clip 36 preferably includes a first end 40, a central portion 42, and a second end 44 as shown in phantom in Figure 3. The first end 40 is preferably electrically connected to ground. The central portion 42 is formed with a finger 43 that is bent generally perpendicularly to the failsafe clip 36. The finger 43 of the central portion 42 biases the fusible link 34 under normal operating conditions. Preferably the finger 43 is made non-conductive. The second end 44 preferably includes first and second legs 46, 48 which are configured to communicate with the tip and ring 26, 28 when the fusible link 34 fails under excessive current conditions. Preferably contact elements 50, 52 are electrically coupled to the tip and ring 26, 28 to facilitate this communication. Preferably the contact elements 50, 52 are copper. Most preferably the contact elements 50, 52 are coated with solder so that the first and second legs 46, 48 fuse together with the contact elements 50, 52 to provide a low impedance path to ground under conditions of sustained high overcurrent when the failsafe clip is triggered by release of the fusible link.

In the first embodiment of the failsafe mechanism 100, the trigger unit 12 preferably is configured so that the fusible link 34 extends between the heat sensing diode 30 and the thyristor 32 as shown in Figure 3. Preferably the heat sensing diode 30 is a type that can be surface mounted to a printed circuit board 38 as shown in Figure 5 with the fusible link 34 embedded in the solder adjacent to the heat sensing diode 30. Preferably the thyristor 32 is also of a type that can be surface mounted with the fusible link 34 embedded in a similar manner as shown in Figure 5. As shown in Figure 4, the printed circuit board 38 is preferably formed with an opening 54 between heat sensing diode 30 and the thyristor 32. Preferably the failsafe clip 36 is mounted to the printed circuit board 38 on the side opposite the trigger unit 12 so that the finger 43 engages the fusible link 34 to put the fusible link 34 in tension. The tension in the fusible link 34 prevents the first and second legs 46, 48 from communicating with the contact elements 50, 52 under normal operating conditions. In this embodiment, the heat sensing diode 30 and thyristor 32 are preferably connected to the printed circuit board 38 with a solder having a melting point selected to release either the heat sensing diode 30 and thyristor 32 from the printed circuit board 38 when either or both get too hot due to an overvoltage condition. If either the heat sensing diode 30 or the thyristor 32 is released, the failsafe clip 36 will shunt the current to ground. The failsafe clip 36 can also shunt the current without the complete release of either the heat sensing diode 30 or the thyristor 32 from the printed circuit board 38 if the solder at one of the components is heated to release the tension in the fusible link 34.

In the second embodiment of the failsafe mechanism 200, as shown in Figures 6 and 7, the trigger unit 12 preferably is configured so that the fusible link 34 is connected at one end 56 to the ground of the diode bridge 11 , runs under the heat sensing diode 30, and has a tethered end 58 attached to the finger 43 of the failsafe clip 36. The printed circuit board 38 is preferably formed with a slot 60 running through substantially the center o the heat sensing diode 30 to accommodate the fusible link 34 and the finger of the failsafe clip 36. Preferably the slot 60 is "T" shaped as shown in Figure 7. Preferably the failsafe clip 36 is mounted to the printed circuit board 38 on the side opposite the trigger unit 12 so that the finger 43 engages the fusible link 34 to put the fusible link 34 in tension. The tension in the fusible link 34 prevents the first and second legs 46, 48 from communicating with the contact elements 50, 52 under normal operating conditions.

In the previous embodiments, the fastened end 40 (i.e., the end opposite the free ends) of the resilient failsafe clip 36 had been attached to the ground circuit of the printed circuit board so as to short the circuit to ground through the fastened end in a sustained overvoltage condition or an excessive current situation. In such embodiments, it is also desirable to ensure that the finger 43 of the failsafe clip 36 which engages the fusible link (i.e., wire 34) was insulated from the wire by providing the finger 43 with an electrically non-conductive coating, for example.

In another embodiment 300, as shown in Figures 9A, 9B and 10, the resilient failsafe clip 36' is not grounded under normal operating conditions. More specifically, the fastened end 40' of the failsafe clip 36' is not attached to ground but rather is insulated from ground by, for example, mounting the clip directly to the nonconducting phenolic board of the printed circuit board 38. Additionally, the failsafe clip 36" includes three extended legs 46', 48'and 70, rather than two as shown in the previous embodiments. As with the previous embodiments, two of the legs 46' and 48' have their free ends situated over conductive pads 50, 52, which are connected to the tip and ring lines 26, 28. The third additional leg 70 has a free end which is situated over a conductive pad 72 which is connected to the ground of the printed circuit board. Under normal conditions, all three legs 46', 48', 70 are biased away from the underside of the circuit board by the fusible link 34 so as not to be in contact with their respective conductive pads 50, 52, 72.

In a sustained overvoltage situation, the fusible link (i.e., wire 34) will loosen from its solder mounts due to the excessive heat caused by the overvoltage. In an excessive current pulse condition, the fusible link 34 will fail or break, thereby releasing the failsafe clip so that the free ends of the legs 46', 48', 70 engage the conductive pads situated directly under them. In this way, the tip and ring lines 26, 28 will be connected to ground through the three fingers of the failsafe clip.

The portion 43 of the failsafe clip which extends through the slot 54 formed through the thickness of the printed circuit board 38 and which engages the fusible link 34 may be formed as a stamped-out portion 73 of the failsafe clip, as shown in Figures 9A and 9B, or may be a shortened, bent-over, finger 74 of the failsafe clip, as shown in Figure 10.

Under conditions of extreme overcurrent, such as a 5,000A short duration pulse, the diodes and thyristor components will suffer extremely fast open circuit failure. This is caused by mechanical separation of the elements comprising these solid state devices. Such open circuit failure response to high current pulses is an unacceptable response for a protector module. The additional purpose for the fusible link is that it will break open under such conditions and the failsafe clip 36 will operate to create a low resistance shunt from Tip and Ring to ground. Thus, the failsafe clip operates via two (2) different modes: 1. Under conditions of sustained moderate overvoltage through melting of the solder holding the thyristor and/or heat sensing diode to the printed circuit board; and

2. Under conditions of short duration high current surges through fuse opening of the link and not necessarily melting of the solder holding the thyristor and/or heat sensing diode to the printed circuit board.

Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention.

Claims

WHAT IS CLAIMED IS:

1 . A failsafe mechanism for protecting telecommunication equipment having a tip and ring from both a sustained overvoltage condition and an excessive current condition, said failsafe mechanism comprising:

a failsafe clip having a first end which is electrically coupled to ground and a second end that is normally biased in an open position with respect to the tip and ring of the telecommunication equipment in the absence of both a sustained overvoltage condition and an excessive current condition;

a diode bridge electrically coupled to the tip and ring of the telecommunication equipment and the ground; and

a trigger unit electrically coupled to the diode bridge and configured to bias said second end of said failsafe clip in said normally open position, said trigger unit releasing said failsafe clip upon either a sustained overvoltage condition or an excessive current condition, whereby said failsafe clip shunts all current to the ground.

2. A failsafe mechanism as defined by Claim 1 , wherein said diode bridge includes a first diode, a second diode, a third diode, and a fourth diode, each of said diodes including an anode and a cathode, said cathode of said first diode being coupled to said cathode of said second diode and defining a first node, said anode of said second diode being coupled to said cathode of said third diode and defining a second node, said anode of said third diode being coupled to said anode of said fourth diode and defining a third node, said cathode of said fourth diode being coupled to said anode of said first diode and defining a fourth node.

3. A failsafe mechanism as defined by Claim 2, wherein said trigger unit is coupled between said second node and said first node.

4. A failsafe mechanism as defined by Claim 2, further including a fifth diode and a sixth diode, each of said fifth and sixth diodes including an anode and a cathode, said cathode of said fifth diode being coupled to said trigger unit, said anode of said fifth diode being coupled to the ground, said anode of said sixth diode being coupled to said trigger unit, said cathode of said sixth diode being coupled to the ground.

5. A failsafe mechanism as defined by Claim f, wherein said trigger unit comprises a heat sensing diode and a fusible link electrically connected with said heat sensing diode, said fusible link biasing said second end of said failsafe clip in said open position in the absence of both a sustained overvoltage condition and an excessive current condition and releasing said second end of said failsafe clip under either a sustained overvoltage condition or an excessive current condition, whereby said failsafe clip shunts all current to the ground.

6. A failsafe mechanism as defined by Claim 5, wherein said fusible link is a conductor wire having a failure point at a known high current condition, whereby, upon failure, said conductor wire releases said failsafe clip from its biased open position.

7. A failsafe mechanism as defined by Claim 5, wherein said trigger unit is disposed on a printed circuit board.

8. A failsafe mechanism as defined by Claim 7, wherein said heat sensing diode is connected to said printed circuit board via a solder having a predetermined melting point, said solder releasing said heat sensing diode from said printed circuit board upon an overvoltage condition, whereby said failsafe clip is released from its biased open position.

9. A failsafe mechanism as defined by Claim 7, wherein said failsafe clip further comprises a central portion having a finger making contact with said fusible link for biasing said failsafe clip in said open position.

10. A failsafe mechanism as defined by Claim 9, wherein said finger is made non-conductive.

1 1. A failsafe mechanism as defined by Claim 1 , wherein said second end of said failsafe clip includes first and second legs being configured to respectively electrically communicate with the tip and ring of the telecommunication equipment when said failsafe clip is released from its biased open position.

12. A failsafe mechanism as defined by Claim 1 1 , wherein at least one of the tip and ring includes a fusible contact element for permanently fusing with the respective first or second leg of said failsafe clip when said failsafe clip is released from its biased open position.

13. A failsafe mechanism as defined by Claim 9, wherein said first end of said failsafe clip is mounted on a first surface of said printed circuit board and said trigger unit is mounted on a second surface of said printed circuit board opposite said first surface, said printed circuit board having an opening extending between said first and second surfaces, said finger of said failsafe clip engaging said fusible link of said trigger unit through said opening to bias said failsafe clip in said open position.

14. A failsafe mechanism for protecting telecommunication equipment, having a tip, a ring and ground, from both a sustained overvoltage condition and an excessive current condition, said failsafe mechanism comprising:

a resilient failsafe clip fixed at a first end and having a second end that is normally biased in an open position with respect to the tip, the ring and ground of the telecommunication equipment in the absence of both a sustained overvoltage condition and an excessive current condition;

a diode bridge electrically coupled to the tip, the ring and ground of the telecommunication equipment; and

15. A failsafe mechanism as defined in Claim 14, wherein said trigger unit comprises a heat sensing diode and a fusible link electrically connected with said heat sensing diode, said fusible link biasing said second end of said failsafe clip in said open position in the absence of both a sustained overvoltage condition and an excessive current condition and releasing said second end of said failsafe clip upon either a sustained overvoltage condition or an excessive current condition, whereby said failsafe clip shunts all current to the ground.

16. A failsafe mechanism as defined in Claim 15, wherein said fusible link is a conductor wire having a failure point at a known high current condition, whereby, upon failure, said conductor wire releases said failsafe clip from its biased open position.

17. A failsafe mechanism as defined in Claim 15, wherein said trigger unit is disposed on a printed circuit board.

18. A failsafe mechanism as defined in Claim 1 , wherein said heat sensing diode is connected to said printed circuit board via a solder having a predetermined melting point, said solder releasing said heat sensing diode from said printed circuit board upon an overvoltage condition, whereby said failsafe clip is released from its biased open position.

19. A failsafe mechanism as defined in Claim 17, wherein said failsafe clip further comprises a central portion having a finger making contact with said fusible link for biasing said failsafe clip in said open position.

20. A failsafe mechanism as defined in Claim 14, wherein said second end of said failsafe clip includes first, second and third legs being configured to respectively electrically communicate with the tip, the ring and ground of the telecommunication equipment when said failsafe clip is released from its biased open position,

21. A failsafe mechanism as defined in Claim 20, wherein at least one of the tip, the ring and ground includes a fusible contact element for permanently fusing with the respective first, second or third leg of said failsafe clip when said failsafe clip is released from its biased open position.

22. A failsafe mechanism as defined in Claim 19, wherein said first end of said failsafe clip is fixed on a first surface of said printed circuit board and said trigger unit is mounted on a second surface of said printed circuit board opposite said first surface, said printed circuit board having an opening extending between said first and second surfaces, said finger of said failsafe clip engaging said fusible link of sad trigger unit through said opening to bias said failsafe clip in said open position.