| 摘要 |
PURPOSE:To prevent the welding of a cut-off contact, even if an abnormal voltage is impressed externally, by connecting one of cut-off contacts for each subscriber through multiple and grounding it via a common resistor. CONSTITUTION:When a subscriber telephone set 1 hooks off, a part of current flows in the path of ground-resistor 12-cut-off contact 18b-protecting circuit 3- subscriber line 21b-telephone set 1-subscriber line 21a-protecting circuit 3-cut- off contact 18a-resistor 14-resistor 15-battery and the other part of the current flows in a drive circuit 10 or a reading circuit 11 separately via diodes 16, 17. When the subscriber telephone set 1 hooks on, if a power line contacts the subscriber line 21b of induction takes place, and if a high voltage 23 is impressed since the current is limited with the resistor 12, the welding of the cut-off contact 18b is prevented. |
