ADJUSTABLE INTEGRATED/DISCRETE-ELEMENT LINE CURRENT CONTROLLER IN A TELEPHONE SET

摘要

A telephone set having a voltage gain and control circuit element in series with the main current path of a line current control transistor, connected between first and second line end portions. The line current control transistor is connected between the first line end portion and the modulation terminal of the voltage gain and control circuit. A line current measuring resistor is connected between the reference terminal of the voltage gain and control circuit element, and the second line end portion. The rise of line current above a threshold is controlled by a second transistor connected between a threshold voltage source and the control electrode of the line current control transistor. The second transistor is also controlled by a compensating diode connected between the control electrode of the second transistor and the line current measuring resistor.