| 摘要 |
PURPOSE:To facilitate the transfer of talking by using an electronic switch to hold a DC loop at holding and detecting the closing of the DC loop by other telephone set in branch connection to the same line thereby releasing the holding state automatically. CONSTITUTION:A capacitor 17 is charged through a resistor 15 and a diode 16 at on-hook holding state. In forming the branch state, a current flowing to a closed DC loop is reduced and the line voltage is decreased. When the voltage at the anode side of the diode 16 is lowered, the electric charge charged in the capacitor 17 is discharged through the emitter and base of a transistor (TR) 20, which is turned on and the electric charge in the capacitor 17 turns on a TR 26 through a resistor 24. When the TR 26 is turned on, a signal of H L is caused at a terminal 13b and the signal becomes a holding reset signal.
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