Telephone subscriber line voltage supply circuit - has transistors which connect lines to voltage source in telephone exchange

摘要

An electronic supply bridge in a telephone exchange is arranged to connect a subscriber line pair to a central voltage supply. The bridge consists of at least one current source and at least one current sink for each branch. The emitter-collector circuit of a transistor is connected between the output poles of the current source and the current sink. An alternative embodiment is used which maintains the source current with a high degree of precision. It includes a differential amplifier in the emitter-base circuit of the regulating transistor. One input is connected across the emitter resistor and the other across a tapping on the base potential divider.