Patent ID: 6668060
Filing Date: 2003-12-23
Classification: H04M

Abstract:
A circuit for supplying DC power voltage to a subscriber line interface circuit (SLIC) coupled to respective tip and ring portions of a telephone line comprising:first and second input terminals adapted to be coupled across a source of DC supply voltage; first and second output terminals adapted to be coupled to power supply terminals of said SLIC; and a switchmode power converter circuit coupled to said first and second input terminals and to said first and second output terminals, and having a voltage sense input coupled to said respective tip and ring portions of said telephone line, and being operative to supply a prescribed DC supply voltage to said power supply terminals of said SLIC relative to the voltage level of one of said respective tip and ring portions of said telephone line as sensed by said voltage sense input during application to said telephone line of balanced ringing signals by said SLIC, and wherein said switchmode converter comprises a comparator having first and second inputs, said first input being coupled to a DC-DC output node downstream of a MOSFET switch installed in a DC supply rail of said source of DC supply voltage, said DC-DC output node being coupled to a power supply terminal of said SLIC, and a second input coupled to a set point node, said set point node being coupled through a voltage offset path to each of said respective tip and ring portions of said telephone line, and wherein said voltage offset path includes a voltage offset device coupled via respective diodes to said tip and ring loop portions of said telephone line, and further including at least one smoothing filter circuit coupled in a circuit path that includes said DC-DC output node.