| 摘要 |
PCT No. PCT/SE87/00582 Sec. 371 Date Jun. 21, 1988 Sec. 102(e) Date Jun. 21, 1988 PCT Filed Dec. 8, 1987 PCT Pub. No. WO88/04502 PCT Pub. Date Jun. 16, 1988.The invention relates to an apparatus for powering a loudspeaker amplifier (5) in a telephone set fed with a line current (ILO) from a telephone line (3). An incoming speech signal (S) is amplified (8) and sent to a loudspeaker (4) via the amplifier (5), which is powered via its feed connections (19, 20) from a reservoir capacitor (6). By the capacitor feed there are avoided variations in the line current (ILO) on amplification of the speech signal (S). The capacitor is recharged with the aid of the speech circuit (13), which has an amplifier means (16, 17) sensing a line voltage (UO) via a voltage sensing circuit (18). The amplifier means (16, 17) steers the line current (ILO) to a constant value responsive to the line voltage (UO) by sending a current (16) to the line (3) via a resistor (R1), thus keeping constant a current (14) through the resistor (R1), this current being sensed by the amplifier means. The reservoir capacitor (6) is connected via a controllable current generator (22) to the resistor (R1) and a circuit (24), which senses the voltage across the resistor (R1) and controls the generator (22). The reservoir capacitor (6) is charged by a current (15) through the current generator (22) and the amplifier means (16, 17) controls its output current (16) such that the current (14=15+16) through the resistor (R1) is kept constant. The apparatus utilizes the existing speech circuit (13) to keep the line current (ILO) constant at the power supply. |
