Battery feed circuit for supplying feed current to telephone set

A battery feed circuit for supplying a feed current to a telephone set via a 2-wire telecommunication line formed of a first line and a second line, said battery feed circuit comprising:

• first voltage detection means for detecting a first voltage across said first line and a ground line having an electric potential of zero and for outputting a first output current corresponding to said first voltage;
• second voltage detection means for detecting a second voltage across said second line and a power line connected to a power supply of said battery feed circuit and for outputting a second output current corresponding to said second voltage;
• current source means responsive to a first control signal for respectively generating first and second currents in said first and second lines, said first and second currents in said first and second lines being equal in magnitude and opposite in direction, said current source means also varying said first and second currents in said first and second lines in response to a common mode voltage across said first and second lines;
• first feedback means responsive to the first and second voltages detected by said first and second voltage detection means for generating said first control signal, said first feedback means comprising current addition means for adding said first current from said first voltage detection means and said second current from said second voltage detection means to each other, and current limit means for limiting a current obtained by said current addition means so as to not exceed a predetermined value, said first feedback means generating said first control signal based on a current obtained by said current limit means;
• and
• second feedback means for generating said second control signal by detecting the common mode voltage across said first and second lines.