| 摘要 |
PROBLEM TO BE SOLVED: To enable both an analog system and a digital system to be applied by blocking an analog sound signal by an electronic choke circuit and a digital sound signal by a choke coil so that they do not leak to a power source part. SOLUTION: A voltage and a current of subscriber's lines 13 and 14 are detected by a voltage/current detection circuit 15 and a DC/DC converter 20 is controlled by way of a controller 50. In the case of analog subscriber, the DC/DC converter 20 is controlled so that a voltage drop corresponding to 400 Ωfrom 48 V is imitated. Electronic choke circuits 11 and 12 are constant current circuit for using an operational amplifier or the like, block only sound frequency (from 100 Hz to 4 kHz), while choke coils L11 and L12 are coils of several meter henries and block only a frequency element (a high frequency element) of a digital signal. Both of these chokes are inserted serially to the DC/DC converter 20. |
