| 摘要 |
PURPOSE:To prevent a storage content such as abbreviation dial from being lost because of non-feeding state of a dial memory when the memory is disconnected from a telephone line while being off-hook by switching power depending on the output of a current supply circuit in place of the state of a hook switch. CONSTITUTION:When off-hook takes place, a hook switch HS is closed and a DC voltage decide by the DC resistance of a talking circuit 4 is produced at a point P. Since the DC voltage of the talking circuit 4 is 3.0V or, above with respect to the DC bias point of a transmission amplifier, a voltage applied to the cathode of a diode D4 is not lower than 2.3V in the worst feeding condition even when the emitter-collector voltage drop of a transistor Q3 and the voltage drop of a diode D1 are subtracted. Since the voltage is higher, off course, then the worst voltage in the voltage state connected to a general subscriber line, the diode D4 as a discharge is turned off, the discharge circuit of a battery BT is interrupted and no power of the battery BT is consumed during this time. |
