| 摘要 |
<p>PURPOSE:To eliminate the need for a contact of a hook switch which interrupts current to a control circuit and a magnet at on-hook, by providing a capacitor for control operation and for a backup power supply separately. CONSTITUTION:At off-hook, capacitors 17, 18 are charged up to a voltage determined with a constant voltage characteristic of a Zener diode 11 with a call current. Further, at off-hook, a minute current is applied to the capacitor 18 only via a high resistance 13 and the capacitor is charged up to a voltage determined with a constant voltage characteristic of a Zener diode 12. A terminal voltage of the capacitor 17 is applied to an ROM72, a CPU73, and a magnet 8 as a control power supply and a terminal voltage of the capacitor 18 is applied to an RAM7 as a backup power supply. Charges charged in the capacitor 18 in this case are prevented from flowing to a control circuit 7 and the magnet 8 due to a diode 16, then contacts of a hook switch are not required.</p> |
