Gte Communication Systems Corporation

Gte Lenkurt Incorporated

John M Huft

Frederick J Kiko

An active current limited in only the ring side of a telephone circuit has the control branch of a current mirror resistively connected across a supply voltage for establishing the magnitude of loop current in its other branch. A first resistor is also connected between adjacent one sides of the two branches for causing the control voltage and loop current to vary as a function of loop length. Extraneous metallic voltages on the A and B leads are AC coupled to associated inputs of a differential amplifier having its output connected through a second resistor to the one side of the control branch for modulating the loop current provided by the other branch. Opposite sides of the second resistor are fed back to associated input terminals of the amplifier. The amplitude modulated loop current is also fed back to an input of the amplifier for minimizing the affects of induced metallic voltages on the tip and ring lines.

Auto-balance circuit for battery feed in a telephone circuit

A ring-ground circuit in a telephone system comprises a control transistor that selectively receives base drive from a microprocessor and that has its emitter connected through a low voltage LED and through the series combination of the base-emitter junction of a switching transistor and its emitter resistor to ground. The LED has a sharp transition in its conduction characteristics when the voltage across it reaches a predetermined value which is a reference voltage. Conduction of the control transistor provides base drive to the switching transistor for causing collector current in the latter to initiate a ground-start condition in a relay coil that is connected to a central office battery voltage. When current in the switching transistor increases to a prescribed value, that is set by the LED reference voltage and the emitter resistor, conduction of the switching transistor is automatically controlled for limiting the maximum value of its collector current.

Current limiter for telephone office signalling

An active current limiter in only the ring side of a telephone circuit has the control branch of a current mirror resistively connected across a supply voltage for establishing the magnitude of loop current in its other branch. A first resistor is also connected between adjacent one sides of the two branches for causing the control voltage and loop current to vary as a function of loop length. Extraneous metallic voltages on the A and B leads are AC coupled to associated inputs of a differential amplifier having its output connected through a second resistor to the one side of the control branch for modulating the loop current provided by the other branch. Opposite sides of the second resistor are fed back to associated input terminals of the amplifier. The amplitude modulated loop current is also fed back to an input of the amplifier for minimizing the affects of induced metallic voltages on the tip and ring lines.

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Lakewood, CO, United States of America

John M Huft