| 摘要 |
<p>A voltage regulating power supply 23 is connected in series with an ac load 22 between two wires 1 and 3 of a telephone line. A dc load 21 comprising a simulated inductance is connected by a switch 24: either, in parallel only with the ac load 22; or, when the line voltage V1 drops threatening to prevent operation of the simulated inductance, in parrallel with both the voltage regulator 23 and the ac load 22. The use of one simulated inductance switched between two modes of operation gives the advantage that a transistor TR1 within the simulatd inductance is always ON and can be used to drive signals onto the telephone line ZL.</p> |
