| 摘要 |
PURPOSE:To keep a current fetched from a line constant as supplying a bias voltage stabilized by a constant voltage source by fetching a constant current from a telephone line by a constant current means, outputting a constant voltage by a constant voltage means setting the current as input, and setting the voltage as the base bias voltage of a transistor. CONSTITUTION:A constant current source 2 is connected with the telephone line, and outputs the constant current II by inputting a line voltage VL. The constant voltage source 3 outputs the contant voltage VBB by inputting the current II. When the voltage VBB is inputted to the transistor 4 as the base bias voltage, the emitter current IE of the transistor 4 goes to (VBB-VBE)/RE. Since the base bias voltage VBB is always kept constant, the emitter current IE can be also kept constant as far as the VBE is kept stably. Consequently, the current fetched from the telephone line can go to the sum of the current II and the emitter current IE, which always enables the constant current to be fetched even when the line voltage VL changes. |
