60/154,446, which was filed on September 17,1999, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention This invention relates to an apparatus for protecting electronic equipment from overvoltage and overcurrent conditions. In particular, this invention protects electronic equipment of a telephone service provider located at a central switching station of a telephone network.

Description of the Prior Art Telephone systems are designed with central switching stations to which telephone lines are connected. The central switching stations route the telephone calls placed by telephone service subscribers. To route the telephone calls, it is necessary to attach very expensive electronic equipment (e. g., switching networks) to the telephone lines. Energy surges, due to lightening, for example, on the telephone lines can damage the electronic equipment. In order to protect the electronic equipment, energy surge protection circuits are typically placed between the electronic equipment and the telephone lines.

Central switching stations for telephone and communication systems have a large number of incoming transmission lines connected to a switching network. These transmission lines are connected to a series of connection blocks. Each connection block can receive a plurality of transmission lines. In addition, the connection block can receive a plug-type device which, when inserted, results in a connection between

the transmission lines and the switching network. Typically, energy surge protection circuits are plug-type devices, which can be inserted or removed from a switching network socket or receptacle easily.

Prior art surge protection circuits have included fuses, semiconductor devices, heat coils, gas tubes, and combinations thereof. Typically, these circuits can not be manufactured on a printed circuit board because the high level of current experienced during a surge condition destroys the conductive traces on the printed circuit board, which connect the various circuit components.

Further, the plug-type devices that are inserted into the connection blocks have standardized dimensions, which are limited in size. Prior art circuits are unable to use printed circuit boards in combination with large shunting devices, such as gas tubes, because the circuit does not fit within a standard plug assembly. The present invention solves the problems associated with the prior art discussed above.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the present invention to provide a protector circuit and module for protecting telephony equipment from energy surge conditions, which can be manufactured on a printed circuit board.

It is a further object of the present invention to provide a protector circuit and module for protecting telephony equipment from energy surge conditions, which includes a gas dissipation tube mounted on a printed circuit board.

It is an even further object of the present invention to provide a protector circuit and module for protecting telephony equipment from energy surge condition, which includes a fusible connection to protect electronic components on a printed circuit board.

In accordance with one form of the present invention, a protection circuit includes a three-element gas dissipation tube having a first element connected to a telephone tip input signal, a second element connected to a telephone ring input signal, and a third element connected to ground. A first series resistor connects the first element to a telephone tip output signal, and a second series resistor connects the second element to a telephone ring output signal. A diode bridge, which preferably includes seven diodes, is connected between the tip and ring signals.

The components in the protection circuit are mounted on a printed circuit board having connectors that connect to the telephone lines, electronic equipment, and ground. The printed circuit board defines a hole, which is preferably adjacent to the connectors. In the preferred embodiment, the gas dissipation tube is partially recessed into the hole to reduce the circuit profile. The connection between the resistors or the diode bridge and the tip and ring signals may be fusible traces laid out on the printed circuit board, which melt in response to a power surge occurring on the tip and/or ring signals.

These and other objects, features, and advantages of the present invention will be 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 Figure 1 is a schematic diagram of one embodiment of a protection circuit formed in accordance with the present invention.

Figure 2 is a pictorial representation of one embodiment of the protector module formed in accordance with the present invention, which includes a fail-safe circuit.

Figure 3 is a pictorial representation of a gas dissipation tube including the fail-safe circuit used in the embodiment of the protector module shown in Figure 2.

Figure 4 is a pictorial representation of a protector module, which is substantially identical to that of Figure 2 except that the gas dissipation tube utilizes a different fail-safe mechanism.

Figure 5 is an exploded pictorial representation of a plug assembly including the protector module.

Figure 6 is a pictorial representation of an assembled plug assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In one form, the present invention relates to an apparatus for protecting electronic equipment from energy surges. A schematic diagram of one embodiment of an energy surge protection circuit is illustrated in Figure 1. The energy surge protection circuit includes a gas dissipation tube 2 having a first element 2a, which is connected to a tip input line 4, a second element 2b, which is connected to a ring input line 6, and a third element 2c, which is connected to ground.

A tip resistor 8 is electrically connected in series between the first element 2a and a tip output line 12. A ring resistor 10 is electrically connected in series between the second element 2b and a ring output line 14. Preferably, the tip resistor 8 and ring resistor 10 have a resistance of about 5.1S2 (ohms).

A clamping circuit, which includes seven diodes, is connected between the tip output line 12, the ring output line 14, and ground. The connectivity of the clamping circuit will now be described. The cathode of a first diode 16 is connected to the tip output line 12, and its anode is connected to a first juncture 20. The anode of a second diode 18 is also connected to the tip output line 12, and its cathode is connected to a

second juncture 22. The cathode of a third diode 24 is connected to the ring output line 14, and its anode is connected to the first juncture 20.

The anode of a fourth diode 26 is connected the ring output line 14, and its cathode is connected to the second juncture 22. The anode of a fifth diode 28 is connected to the first juncture 20, and its cathode is connected to ground. The cathode of a sixth diode 30 is connected to the second juncture 22, and its anode is connected to ground. The cathode of a seventh diode 32 is connected to the second juncture 22, and its anode is connected to the first juncture 20. The seventh diode 32 is preferably a transient-voltage-suppression (TVS) diode. The first juncture 20 and the second juncture 22 are not components of any kind, but are merely points at which electrical connections are made between components.

In operation the energy surge protection circuit shown in Figure 1 dissipates energy surges, which are on the tip line, the ring line, or ground. An energy surge on any of the lines causes the gas dissipation tube to begin charging. A positive energy surge on the tip input line 4 causes the second diode 18 and the fifth diode 28 to turn on, and the energy surge is clamped by the seventh diode 32. A positive energy surge on the ring input line 6 causes the fourth diode 26 and the fifth diode 28 to turn on, and the energy surge is clamped by the seventh diode 32.

Similarly, a negative energy surge on the tip input line 4 causes the first diode 16 and the sixth diode 30 to turn on, and the energy surge is clamped by the seventh diode 32. A negative energy surge on the ring input line 6 causes the third diode 24 and the sixth diode 30 to turn on, and the energy surge is clamped by the seventh diode 32.

The characteristics of the clamping circuit (diodes 16,18,22,24,26, and the clamping diode 32) and the gas dissipation tube 44 are chosen such that the protective functions of these devices are integrated into an overall scheme designed to protect sensitive electronic equipment under a variety of different circumstances. Each of the diodes are preferably selected to react almost instantaneously (i. e., within

nanoseconds) to an energy surge. In contrast, the gas dissipation tube 44 preferably responds to an energy surge in about 10 microseconds or less.

The clamping diode 32 is preferably selected to clamp the energy surge at a voltage level that is safe for the electronic equipment connected to the lines, but typically fails in about 12 microseconds when subjected to about 125 amps. The threshold voltage of the clamping diode 32 is preferably chosen to be greater than the breakdown voltage of the gas dissipation tube 44.

Thus, in response to an energy surge, the clamping diode 32 initially diverts the excess current flow within nanoseconds. Since the threshold voltage of the clamping diode 32 is greater than the breakdown voltage of the gas dissipation tube 44, the gas dissipation tube 44 can begin its response to the overvoltage condition while the clamping diode is diverting the excess current.

The clamping diode is able to withstand the excess current until the gas dissipation tube 44 is able to respond and short the excess current to ground within 10 microseconds or less, which is well before the clamping diode 32 would fail (i. e., about 12 microseconds). Thus, the slower gas dissipation tube 44 has enough time to fully charge and dissipate or crowbar the excess energy before either the clamping circuit or electronic equipment is damaged.

The energy surge protection circuit of the present invention is mounted on a printed circuit board 3. A pictorial diagram illustrating the energy surge protection circuit mounted on the printed circuit board 3 is shown in Figure 2. The printed circuit board 3 includes a front portion 3a and a rear portion 3b. The front portion 3a includes contacts 34,38,40,42, and 44 fastened to it.

The contacts 34, 38,40, and 44 can be any type of electrical contact known in the art, but preferably include two resilient conductors pressing against one another between which a third conductor may be inserted to form an electrical connection.

The contact 42 may be any type of electrical contact known in the art, but is preferably

a pin-type device extending from the circuit, which can be inserted into a socket to form an electrical connection.

A gas dissipation tube 44 is connected to the contacts. Contact 34 is connected to a first element 44a, and contact 44 is connected to a second element 44b.

Contact 42 is connected to a third element 44c and functions as a ground line.

Contact 38 is the tip output line, and contact 40 is the ring output line.

The printed circuit board 3 defines an aperture or hole, which is dimensioned such that the gas dissipation tube 44 may be partially submerged or recessed within the hole when connected to the circuit. This allows the circuit to have a smaller profile that enables it to fit in a standard-sized plug-type device. Preferably, the gas dissipation tube is submerged into the printed circuit board 3 until it is flush with the bottom surface of the printed circuit board 3. The elements of the gas dissipation tube are preferably soldered to their respective contacts.

The gas dissipation tube 44 is preferably positioned contiguous to the front portion 3 a of the printed circuit board 3 such that the trace conductors on the printed circuit board will not be required for connections to the gas dissipation tube. It is preferable to connect the gas dissipation tube with conductors that are able to withstand relatively large amounts of power compared to the trace conductors.

Therefore, the elements of the gas dissipation tube are soldered directly to contacts 34, 42, and 44. Trace conductors on the printed circuit board could not withstand the surge currents experienced by the gas dissipation tube 44 and would melt under such conditions if they were used to connect the gas dissipation tube to the contacts 34,42, and 44.

Manufacturing the protection circuit on a printed circuit board is less expensive, faster, and more reliable than manufacturing the same circuit without a printed circuit board. The gas dissipation tube is able to be mounted on a printed circuit board due to the partial submersion of the gas dissipation tube, which enables

the circuit to have a smaller profile, and also because the gas dissipation tube is connected directly to the contacts.

The tip resistor 8, the ring resistor 10, and the diodes 16,18,24,26,28,30,32 are mounted to the printed circuit board 3 on the back portion 3b. These discrete components are connected to one another in accordance with the schematic diagram shown in Figure 1 by trace conductors laid out on the printed circuit board 3 as is well known in the art. Of particular interest, are the trace conductors 5,7 shown in Figure 2. Trace conductor 5 connects the ring resistor 10 to the ring input line 6, and trace conductor 7 connects the tip resistor 8 to the tip input line 4.

In a preferred embodiment, the trace conductors 5,7 are designed such that an energy surge, which exceeds the maximum power limits of the individual components, melts the conductors 5,7, thereby opening the circuit and protecting the discrete components. The gas dissipation tube 44 then dissipates the energy surge. It is anticipated that such fusible traces or conductors 5,7 may be manufactured on a circuit board to a nominal thickness and then cut to a desired thickness using techniques well known in the prior art, such as laser trimming.

The gas dissipation tube 44 preferably includes a fail-safe circuit 54.

Referring to Figure 3, the fail-safe circuit 54 will now be described in detail. On a portion of the gas dissipation tube 44, the portion hidden from view in Figure 2, the fail-safe circuit 54 is mounted to the gas dissipation tube 44. A sheet of insulating or insulative material 52, preferably polycarbonate thermoplastic, is wrapped on a portion of the perimeter of the gas dissipation tube 44. The insulating material 52 extends from end-to-end on the gas dissipation tube 44.

A cut is then made defining a hole, which corresponds in position to the third element 44c of the gas dissipation tube 44. A conductor having three portions is then attached to the gas dissipation tube 44. Portion 48 is soldered to the third element 44c. Portions 46 and 50 are resiliently connected to portion 48 such that they are biased towards the first element 44a and the second element 44b, respectively. It is

important that the insulative material 52 be able to withstand the long term pressure that will be exerted on it by the resilient conductors of portions 46,50 to avoid cold flowing (i. e., over a very long period of time a hard object pressing against a soft object, even with a very small amount of force, will begin to deform the soft object and pass through the soft object).

A so-called"power cross"occurs when, for instance, a power line becomes electrically coupled to a telephone line. Such a power cross causes the gas dissipation tube 44 to begin conducting excess energy to ground to prevent damage to sensitive electronic equipment coupled to the telephone lines. During the diversion of energy to ground, the gas dissipation tube 44 enters a so-called"glow mode"in which the tube 44 dissipates a substantial amount of thermal energy.

If the power cross remains intact, the gas dissipation tube gets hotter and its breakdown voltage increases. As the breakdown voltage of the gas dissipation tube 44 approaches the threshold voltage of the clamping diode 32, the clamping circuit begins to dissipate excess energy, which may cause the module to ignite.

However, in response to an energy surge that is large enough to heat the gas dissipation tube 44 to a threshold temperature, the insulative material 52 will melt.

The biased portions 46,50 will then come into contact with their respective elements and short these elements to ground, thereby providing a fail-safe path for dissipating the energy surge.

An alternative embodiment is illustrated in Figure 4. The embodiment of Figure 4 is identical to the embodiment of Figure 2, except that the construction of the fail-safe circuit 54 is different. The alternative fail-safe circuit 56 includes a wing having three portions 15,19,21. The wing is mounted to the third element of the gas dissipation tube 44 by means that are known in the art, preferably a screw. The portions 15 and 21 are positioned contiguous to the first element and the second element of the gas dissipation tube 44, respectively.

An insulative material is then placed between the first element end portion 15 and the second element end portion 21. The portions 15,21 are biased towards their respective elements in a similar manner to the fail-safe circuit 54 shown in Figure 3.

The third element of the gas dissipation tube 44 is then connected to the ground contact 42 by a conductor 13, which is connected to portion 19 of the fail-safe circuit 56 on one end and the contact 42 on the other end.

Referring to Figures 5 and 6, the plug assembly will be described in detail.

The dimensions of the plug assembly 82 are standard and well known in the art.

Preferably, contacts 34,44, and 42 are longer than contacts 38,40 so that the plug assembly can be inserted into the connection block receptacle in one of two discrete levels. The first level results in the contacts 34,44 being connected to the outside plant (i. e., the subscribers telephone lines) and contact 42 being connected to ground.

When inserted in the connection block, contacts 34 and 44 connect to the tip input line 4 and the ring input line 6, respectively. At the first level, the surge protection circuit is connected to the outside plant, but the switching network is not connected to the outside plant. This allows central office equipment to be protected from energy surges without connecting the telephone line to the switching network.

The second level of insertion results in the connection of the contacts 38 and 40 to the central switching station network. The network receptacle is adapted to receive the pins and hold the plug assembly securely in place. The energy surge protection circuit thereby protects the electronic equipment in the telephone network.

In an alternative embodiment, the plug assembly includes pins similar to contact 42 for the contacts 34,38,40,44. The connection block then has five sockets into which the pins are received. The pins correspond in length to the length of the contacts in the single pin embodiment. The same set up is used in both embodiments.

Insertion of the long pins results in a partial connection, and insertion of all the pins results in a full connection. It is advantageous and preferable to use the single pin embodiment because it is more cost-effective. The five-pin embodiment has become

the standard in the United States and is used exclusively. The standard in Europe, however, is the single pin embodiment.

The plug assembly 82 includes a cap 62 and a body 60. The body 60 has a top and a bottom. The top includes tabs 68,70, into which protrusions may be received.

The cap 62 includes protrusions 64,66, which are positioned in such a way to be received by the tabs 68,70 when the cap 62 is pressed together with the body 60.

The bottom of the body 60 defines five holes. Hole 72 corresponds in position to contact 42, hole 74 corresponds in position to contact 34, hole 76 corresponds in position to contact 44, hole 78 corresponds in position to contact 40, and hole 80 corresponds in position to contact 38 when the energy surge protector 1 is inserted into the body 60 of the plug assembly 82. The position of these holes also corresponds to the connectors in the connection block, into which the plug assembly is inserted.

In operation, the energy surge protection circuit is inserted into the body 60 using the contact 42 as a guide, and the cap 62 is then snapped together with the body 60 to hold the energy surge protection circuit in place. Figure 6 illustrates a fully assembled energy surge protector plug assembly.

From the foregoing description, it will be appreciated that the circuit and module formed in accordance with the present invention protect telephony equipment from energy surge conditions and can be manufactured on a printed circuit board. It will also be appreciated that the circuit and module include a gas dissipation tube that can be mounted within a recess on a printed circuit board. Further, it will be appreciated that electronic components on the printed circuit board can be protected with a fusible link.

Although the 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.