Automatically resetting protection arrangement for a telephone subscriber line interface circuit

Claim 2

A protection arrangement for coupling telecommunications equipment to a telecommunications line, comprising: a first terminal for connection to the telecommunications line; a second terminal for connection to the telecommunications equipment; switching means closed in normal operation for coupling the first terminal to the second terminal; triggerable surge protection means coupled between the first terminal and a ground terminal; means responsive to surge voltage between the switching means and the second terminal for triggering the surge protection means into conduction; and means responsive to excessive voltage at the first terminal for opening the switching means.

Claim 3

A protection arrangement as claimed in claim 1 wherein the surge protection means comprises a triac and the means for triggering the surge protection means comprises a bidirectional voltage-dependent element.

Claim 4

A protection arrangement as claimed in claim 2 wherein the bidirectional voltage-dependent element comprises a varistor.

Claim 5

A protection arrangement as claimed in claim 1 wherein the means responsive to excessive voltage at the first terminal for opening the switching means comprises rectifying means, coupled to the first terminal for rectifying voltage thereat to produce a rectified voltage, and means responsive to the rectified voltage exceeding a threshold level for opening the switching means.

Claim 6

A protection arrangement as claimed in claim 1 and including resistive means via which the switching means and the surge protection means are coupled to the first terminal.

Claim 7

A protection arrangement as claimed in claim 5 wherein the surge protection means comprises a triac and the means for triggering the surge protection means comprises a varistor.

Claim 8

A protection arrangement as claimed in claim 6 wherein the means responsive to excessive voltage at the first terminal for opening the switching means comprises rectifying means, coupled to the first terminal for rectifying voltage thereat to produce a rectified voltage, and means responsive to the rectified voltage exceeding a threshold level for opening the switching means.

Claim 9

A protection arrangement as claimed in claim 2 and including resistive means via which the switching means and the surge protection means are coupled to the first terminal.

Claim 10

A protection arrangement as claimed in claim 4 and including resistive means via which the switching means and the surge protection means are coupled to the first terminal.

Claim 11

A protection arrangement comprising: two first terminals for connection to a two-wire telecommunications line; two second terminals for connection to a two-wire telecommunications line interface circuit; two switching means each closed in normal operation for coupling a respective one of the first terminals to a respective one of the second terminals; two triggerable surge protection means each coupled between a respective one of the first terminals and a ground terminal; two triggering means each coupled to a respective one of the second terminals for triggering a respective one of the surge protection means into conduction for providing a surge protection path to the ground terminal; diode means for rectifying voltage at the first terminals to produce a rectified voltage; and means responsive to the rectified voltage exceeding a threshold level for opening the two switching means.

Claim 12

A protection arrangement comprising: two first terminals for connection to a two-wire telecommunications line; two second terminals for connection to a two-wire telecommunications line interface circuit; two switching means each closed in normal operation for coupling a respective one of the first terminals to a respective one of the second terminals; two triggerable surge protection means each coupled between a respective one of the first terminals and a ground terminal; two triggering means each coupled to a respective one of the second terminals for triggering a respective one of the surge protection means into conduction for providing a surge protection path to the ground terminal; diode means for rectifying voltage at the first terminals to produce a rectified voltage; and means responsive to the rectified voltage exceeding a threshold level for opening the two switching means.

Claim 13

A protection arrangement as claimed in claim 10 and including two resistive means, wherein each of the two switching means is coupled to the respective one of the first terminals via a respective one of the resistive means.

Claim 14

A protection arrangement as claimed in claim 11 wherein each of the two surge protection means comprises a triac coupled between the ground terminal and a respective junction between the resistive means and switching means.

Claim 15

A protection arrangement as claimed in claim 12 wherein one of the triacs is connected to the respective junction via a zener diode.

Claim 16

A protection arrangement as claimed in claim 13 wherein each of the two triggering means comprises a varistor and a resistor connected in series between the respective one of the second terminals and a control electrode of the respective one of the triacs.

Claim 17

A protection arrangement as claimed in claim 10 wherein each of the two triggering means further comprises a resistor connected between the control electrode of the respective one of the two triacs and the ground terminal.

Claim 18

A protection circuit for coupling telecommunications equipment to a telecommunications line comprising: a first terminal for connection to the telecommunications line; a second terminal for connection to the telecommunications equipment; a controllable switch closed during normal operation and during short term surge conditions to connect the first terminal to the second terminal, wherein said short term surge condition is a surge condition having duration of less than between about 5 ms and 100 ms; a triggerable surge protector coupled between the first terminal and ground, said surge protector providing surge protection at the first terminal; a surge sensor responsive to voltage at the second terminal, said surge sensor triggering the surge protector into operation; means for opening the switch, said means being responsive to overvoltage at the first terminal sustained for a duration greater than said short term surge condition, said opening of the switch causing the surge sensor to cease operation of the surge protector.

Claim 19

A protection circuit for coupling telecommunications equipment to a telecommunications line comprising: a first terminal for connection to the telecommunications line; a second terminal for connection to the telecommunications equipment; a controllable switch closed during normal operation and during short term surge conditions to connect the first terminal to the second terminal, wherein said short term surge condition is a surge condition having duration of less than between about 5 ms and 100 ms; a triggerable surge protector coupled between the first terminal and ground, said surge protector providing surge protection at the first terminal; a surge sensor responsive to voltage at the second terminal, said surge sensor triggering the surge protector into operation; means for opening the switch, said means being responsive to overvoltage at the first terminal sustained for a duration greater than said short term surge condition, said opening of the switch causing the surge sensor to cease operation of the surge protector.