Patent ID: 7092517

Claim:
A method for regulating with minimum power loss a subscriber line interface circuit (SLIC) supply voltage of an SLIC circuit provided within an interface circuit for connecting an analog subscriber terminal to a digital data transmission line, wherein the method comprises the following steps: (a) applying a telephone line measurement feed voltage (V meas ) to telephone connecting lines connecting said analog subscriber terminal to said SLIC circuit; (b) measuring a feed current (I feed ) which flows via the telephone connecting lines when the telephone line measurement feed voltage is applied by means of a coder/decoder (CODEC) circuit of said interface circuit to generate control information data which are emitted to a monitoring circuit of said interface circuit; (c) wherein the monitoring circuit calculates, in response to the control information data indicating the actual measured feed current (I feed ) and data stored in a memory of said monitoring circuit indicating a predetermined nominal supply current (I nom ) for said analog subscriber terminals, the required SLIC supply voltage for said SLIC circuit and applies a control signal to a DC/DC converter circuit, wherein the calculation of the SLIC supply voltage for the SLIC circuit comprises the following steps: (i) calculating a line resistance (R line ) of the telephone connecting lines as a function of the control information data indicating the actual measured feed current (I feed ) and the applied telephone line measurement feed voltage (V meas ); (ii) calculating a telephone line feed voltage (V feed ) which produces the predetermined nominal supply current (I nom ) through the calculated line resistance (R line ); (iii) calculating an internal voltage drop (V drop ) in the SLIC circuit as a function of an internal resistance (R internal ) of the SLIC circuit and of the predetermined nominal supply current (I nom ); and (iv) calculating the SLIC supply voltage for the SLIC circuit by addition of the calculated telephone line feed voltage (V feed ) and the calculated internal voltage drop (V drop ) in the SLIC circuit; and (d) wherein the DC/DC converter circuit converts a battery voltage (V bat ) to the calculated required SLIC supply voltage in response to the control signal received from said monitoring circuit.