| 摘要 |
PURPOSE:To use a component with low dielectric strength by connecting a constant current source having a drooping characteristic in parallel with an internal resistance so as to reduce the power consumption of a telephone line coping flexibly with an operating DC power supply voltage and a subscriber line length. CONSTITUTION:A DC voltage V from a DC power supply 8 is fed to the positive and negative power supply terminals 3, 4 of a subscriber circuit and impressed to positive and negative line terminals 5, 6 via internal resistances 1, 2. The terminals 5, 6 are connected to a telephone set 7 having a DC equivalent resistance RL. The internal resistances 1, 2 have the resistance of R/2. Further, constant current sources 19, 20 are connected to the internal resistances 1, 2 and its current value I is set as (V0-V)/R, where V0 is the power supply voltage of a conventional circuit. The constant current sources 19, 20 are constant current sources of power consumption type having a drooping characteristic when an impressed voltage is 0. |
