Schnittstellenschaltung für Teilnehmerleitung, die regulierten Strom liefert

摘要

A subscriber line interface circuit (32) provides regulated current to a telephone subscriber (14) in an improved manner by reducing the amount of power required to operate while maintaining a constant current source. The current to the telephone subscriber (14) flows through a switching transistor (92, Fig. 3), and inductive storage element (98, Fig. 3), sensing resistors (54, 56) and a hybrid transformer (38). The desired operating characteristic is obtained by cycling the switching transistor (92). The switching transistor (92) is cycled on at a preset interval causing the telephone subscriber current to flow from the switching transistor. The switching transistor is cycled off in response to an increase in the telephone subscriber current as sensed by the sensing resistors (54, 56) thereby causing the current to flow from the inductive storage element (38). A current sensor (60) coupled to the sensing resistors (54, 56) supplies a current level signal SUMSIG to the switch-mode current source (52) that includes the transistor (92)2 and the inductive storage element (38). Saturation of the transformer (38) is prevented by regulated opposing current supplied by a source (80) controlled by the SUMSIG signal.