Transformer flux compensation circuit

Claim 1

In a transformer-coupled interface circuit for interconnecting two-wire and four-wire telephone communication channels, a transformer flux compensation circuit comprising: a transformer having plural windings magnetically coupled by a common core, a first and a second of said windings being connected to a two-wire telephone channel having tip and ring wires, said first winding being connected between one terminal of a direct current (DC) source of electric power and said tip wire, said second winding being connected between a second terminal of said power source and said ring wire, a third of said windings being a bucking winding, and a fourth of said windings being coupled to said four-wire telephone communication channels, said power source inducing a primary current flow via said first and said second windings into said two-wire channel; means coupled between said first winding, said second winding, and said power source for sensing a flow of said primary current in said two-wire channel; means driven by said sending means for applying current to said bucking winding, the amount of current supplied by said applying means being sufficient to induce a flux in said core by said bucking winding which cancels a flux induced in said core by the flow of said primary current in said first and said second windings, thereby permitting a reduction in the size of said core; a lag-lead stabilization network connected within said applying means for stabilizing the operation of said applying means; and wherein said applying means comprises a driver amplifier and a transistor driven by said amplifier; and wherein said stabilization network comprises two resistors serially connected along a signal path between said driver amplifier and said transistor, and a capacitive branch grounding a junction of said two resistors.