| 摘要 |
PURPOSE:To reduce power consumption of subscriber circuits by temporary power down of a part concerning with DC loop monitoring function of subscriber's circuit of a telephone exchange. CONSTITUTION:A semiconductor switch 2 and transistors 13, 14 are made suspended state by sending a signal of specified period from a power down control circuit 19. That is, in a period T1, all subscriber's circuits are power downed by making transistors 13, 14 suspended state. In a period T2, the lines are charged slowly shifting DC feed internal resistance from high state to low state by operating transistors 13, 14 slowly. The change is shown by a solid line. In a period T3, when a subscriber calls making DC feed possible lowering DC feed internal resistance, detection output can be outputted. The time and period of T3 are determined by minimum scanning interval of call monitoring of a subscriber. |
