| 摘要 |
PURPOSE:To enable calling and trunk line incoming in case of a power failure by using a cable for control signal transmission and a cable for power supply as bypasses for trunk line transfer for the power failure. CONSTITUTION:A couple of cables 21 are connected to a DC power source in a feed state through power failure switching circuits 2, 2-1, and 2-2, or to the trunk line side of a channel switch 8 through a rectifying circuit 4-7 in case of a power failure to apply a voltage having the opposite polarity to that of the DC power source. Further, when incoming signal detecting circuits 30-37 generate outputs 35-1 and 35-2, connections with trunk line sides are made and a sounding device 40 is connected. In the feed state, power source circuits 12, 13, and 16 of the telephone set are connected and in case of a power failure, they are disconnected through a diode 9. When an incoming signal arrives, the detecting circuits 30-37 send outputs 35-1 and 35-2 after a capacitor 41 is charged by the outputs of rectifying circuits 4-7. |
