Transformerless digital-line battery feed circuit

Abstract

A transformerless battery feed circuit for a digital telecommunications line (100) presents a high impedance to digital signals and a low impedance to direct current, and provides a constant-voltage feed with current limiting. The battery feed circuit comprises a pair of transformerless controlled current sources, one for each lead (T,R) of the line, each taking the form of a high-gain transistor (Q1, Q2) having a collector coupled to a source of power (e.g., a battery V1), a base resistively coupled to the power source and capacitively coupled to its corresponding lead, and an emitter coupled to its corresponding lead. The battery feed circuit further comprises a pair of control circuits, one for each current source, each taking the form of a transistor (Q3, Q4) having a collector coupled to the base of the corresponding high-gain transistor, a base resistively coupled to the emitter of the corresponding high-gain transistor and to the power source, and an emitter coupled to the corresponding lead.

Dependencies are inferred from the claim text.