Patent ID: 6498849
Filing Date: 2002-12-24
Classification: H04M,Y02D

Abstract:
In a subscriber line interface circuit comprising a first and a second current amplifier connected with their output terminals to respective wires of a two-wire transmission line to a load, wherein the first current amplifier is connected with its current supply terminal to ground, an arrangement for automatically switching the current supply terminal of the second current amplifier between different DC voltage sources to reduce power losses in the subscriber line interface circuit, whereina line current detecting device is connected to detect line currents below a threshold value, the current supply terminal of the second current amplifier is connected to an output terminal of a voltage regulator, and, via a diode, to a first battery to normally be supplied from said first battery with a substantially constant voltage for line currents above the threshold value, the voltage regulator is connected with its current supply terminal to a second battery of higher absolute voltage than said first battery, and with its input terminal to an output terminal of the line current detecting device, the line current detecting device, in response to line currents below said threshold value, is adapted to output control signals that are proportional to the detected line currents to control the output terminal of the voltage regulator to voltages to reverse bias the diode and to supply the current supply terminal of the second current amplifier as well as the load with a unique voltage for every value of the line current below said threshold value.