Telephone line power supply unit - has multiple winding transformer and compensating winding for effects of primary windings

摘要

A telephone line power supply unit is used to provide current to lines and exchanges. It operates from a d.c. supply. The unit has a transformer (TR) with two primary windings (A, B) one secondary winding (S) and a compensating winding (C). The two primary windings are interconnected by a capacitor (C1). The compensating winding (C) is supplied by a transistor (T) circuit excited by the lines (L1, L2) current. This compensating winding (C) provides a magnetising field to compensate the effects of the two primary windings (A, B). A diode (D) in series with one side of the lines (L1, L2) is used to compensate for the voltage drop in the emitter-base of the transistor (T).