JPS6439162A - Method for setting constant current of analog terminal equipment connected to telephone line - Google Patents

Abstract

PURPOSE:To minimize the electric power of a switchboard and to realize reduction of the electric power supplied to a station, by using a constant current setting circuit to supply a direct current to a telephone circuit to actuate and hold the relay operation of the switchboard regardless of the resistance of the telephone line. CONSTITUTION:When a loop forming part 3 is turned on and an analog terminal equipment is connected to a switchboard, the DC connection is secured between two lines of a telephone line 5 via the part 3 and a constant current control part 2. The part 2 supplies the minimum current necessary for actuating and holding the relay operation of the switchboard. In other words, the part 2 supplies a direct current necessary for said operation of the switchboard regardless of the resistance (circuit length) of the circuit 5. Thus the electric power of the switchboard is minimized. The part 2 serving as a constant current setting circuit consists of a transistor Tr, a resistance R, a Zener diode ZD, a constant current diode CR, etc. The constant current value is controlled and set by the resistance R. While the input/output signal of a signal input/output circuit 1, i.e., an AC component undergoes input/output against the two lines of the line 5 via a transformer of 600 and a capacitor C.