Current limiting and resistance monitoring circuit

Claim 2

A circuit for limiting the amount of direct current flow in a telephone loop connection and providing a signal that is a function of the resistance of the telephone loop connection comprising: current limiting circuit means for connection in series with a direct current power source and a telephone loop connection, responsive to the resistance of the telephone loop connection, for limiting the amount of direct current flow therein within a preset range, and circuit means connected to said current limiting circuit means, responsive to the potential drop across the current limiting circuit means, for providing a signal that is a function of the resistance of the telephone loop connection.

Claim 3

A circuit for limiting the flow of curRent through a telephone loop connection and for monitoring the resistance thereof comprising: a first pair of terminals for connection to a direct current power source; a second pair of terminals for connection to a telephone loop connection including a direct current path; a first and a second control device, each having first and second terminals defining a controllable current path therebetween and a third terminal for controlling the current flow through the controllable path; first circuit means for connecting the first, the second and the third terminals of said first control device between said first and said second pairs of terminals so that said first control device limits the amount of current flow to the telephone loop connection connected across said second pair of terminals and having the first and the second terminals of said first control device defining a series circuit between one of the terminals of each of said first and said second pairs of terminals, and second circuit means for connecting the first and the third terminals of said second control device across at least a portion of said series circuit so that said second control device provides a signal that is a function of the resistance of the telephone loop connection across the second pair of terminals.

Claim 4

A circuit for limiting the flow of curRent through a telephone loop connection and for monitoring the resistance thereof comprising: a first pair of terminals for connection to a direct current power source; a second pair of terminals for connection to a telephone loop connection including a direct current path; a first and a second control device, each having first and second terminals defining a controllable current path therebetween and a third terminal for controlling the current flow through the controllable path; first circuit means for connecting the first, the second and the third terminals of said first control device between said first and said second pairs of terminals so that said first control device limits the amount of current flow to the telephone loop connection connected across said second pair of terminals and having the first and the second terminals of said first control device defining a series circuit between one of the terminals of each of said first and said second pairs of terminals, and second circuit means for connecting the first and the third terminals of said second control device across at least a portion of said series circuit so that said second control device provides a signal that is a function of the resistance of the telephone loop connection across the second pair of terminals.

Claim 5

A circuit as defined in claim 2 wherein: said control devices are transistors, and said first, said second and said third terminals of said devices are respectively the emitter, the collector, and the base of the transistors.

Claim 6

A circuit as defined in claim 3 wherein: the emitter and the collector of the transistor corresponding to the first control device define the controllable current path and the base of said transistor provides a biasing signal responsive to the resistance of the telephone loop connection to limit the current flow through the telephone loop connection within a preset range.

Claim 7

A circuit as defined in claim 4 wherein the emitter and the base of the transistor corresponding to said second control device are connected across the series circuit including the transistor corresponding to the first control device so that a signal is generated at the collector of the transistor which corresponds to said second control device which is a function of the resistance of the telephone loop connection.