EXCHANGE DEVICE, SUBSCRIBER INTERFACE CIRCUIT AND POWER FEEDING METHOD FOR THE CIRCUIT

PROBLEM TO BE SOLVED: To suppress the power consumption of a subscriber interface circuit, to improve dial pulse reception characteristics and to improve the quality of the subscriber interface circuit. SOLUTION: The subscriber interface circuit 111 has a power feeding circuit for feeding either a first voltage or second voltage higher than the first voltage to a subscriber's line and a switching circuit 109 for switching the first voltage and the second voltage as a voltage to be supplied to the subscriber's line. An arithmetic part 104 monitors a current value on the subscriber's line and detects the break state of continuing the state of the current value lower than a predetermined current value for predetermined time. When the break state is detected, the switching circuit 109 switches the voltage to the second voltage. Next, the current value on the subscriber's line is monitored and when the state of the relevant current value higher than the predetermined current value is continued for the predetermined time, the voltage is switched to the first voltage.