Gte Lenkurt Incorporated

Gte Automatic Electric Incorporated

Frederick J Kiko

John M Huft

Thomas J Barzen

John M Huet

The A and B leads of a telephone circuit are resistively connected to the drain and source of an FET switch having its gate connected to the emitter of an optoelectric transistor that is also resistively connected across these leads. The collector of a control transistor is also connected to the gate, with its base-emitter diode and emitter bias resistor connected across the source bias resistor for turning on the control transistor and limiting current in the FET when conduction of the latter exceeds a prescribed rate.

Switching circuit including current limiting and initializing signal

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 circuit for increasing the inductance of a transformer as used in a telephone line circuit. An operational amplifier with appropriate feedback is connected across a separate winding of the transformer to provide the reactive inductance. To compensate for changes in resistance of the winding, a field effect transistor is controlled by the same amplifier output to provide a positive resistance in the feedback path and thus maintain balance.

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Aurora, CO, United States of America

Frederick J Kiko