Current supplying circuit with shorted-to-ground fault detecting function

Abstract

This invention relates to a current supplying circuit for supplying a current to a terminal apparatus through a ring line and a tip line which are connected through resistance elements to a potential source and ground, respectively. This current supplying circuit includes respective detectors for generating first and second detection signals of amplitudes proportional to the currents flowing in the ring and tip lines, respectively, a circuit for generating a reference signal, and a comparator for comparing the signal difference between the first and second detection signals and the reference signal so as to produce a signal in accordance with the compared result, thus a shorted-to-ground fault on the ring line or tip line being detected by monitoring the signal produced in accordance with the compared result. After the shorted-to-ground fault is detected, the current supplying circuit is protected from breakdown.