| 摘要 |
PURPOSE:To improve a calling quality by providing a means capable of setting the power source of an active element at either of a telephone line or a direct current power source and securing the direct current power source. CONSTITUTION:An input from circuit terminals L1 and L2 is inputted through a rectifying circuit 3 and a hook switch 7 to a line switch 13. The switch 13 is driven by a dialer IC 10, and its output is inputted to a calling network circuit 8, which is the active element. One of the circuit of the switch 13 is inputted to transistors(TR)1 and 3 of a power source supplying open path 11. The input of the circuit 11 supplies the current from a diode D3 when a VDC exists, and from a diode D2 when it does not exist to the IC10 in an off-hook condition. The power source of the IC10 is normally supplied from a battery VDC, whereas, when a trouble occurs at the direct current power source VDC, the voltage is detected by the IC10, the power source is switched to the circuit 8, and supplied from the telephone set. Thus, the direct current power source is secured, and the calling quality is improved. |
