| 摘要 |
PURPOSE:To reduce power consumption during disuse, to decrease a power voltage supplied from a switchboard, and to stabilize operation by inverting the polarity of a DC power source supplying electric power from the switchboard during calling operation and then by sending a call code signal. CONSTITUTION:When the handset of a digital telephone set is put off the hook while the digital telephone set is originating, a hook switch 3 is closed to form a DC loop including a switchboard, and once a power source circuit 5 rises, the switchboard detects the calling of the telephone set. During calling operation, the polarity of DC electric power supplied from the switchboard is inverted, and consequently a diode 7 conducts; and then a power source circuit 11 rises to close an electronic switch 4, thereby operating a digital telephone set circuit body 16 and a call signal detecting circuit 12. A call code signal is detected by a detecting circuit 12 and an electronic switch 14 is closed to drive a calling circuit 13, thereby calling a party subscriber. When the handset is put on the hook after a telephone call, the hook switch 13 is opened to reset the polarity of the DC electric power supplied from the switchboard. |
