| 摘要 |
A pulse data signal and a DC power signal are transmitted over a pair of transmission lines interconnecting a main operating unit and telephone sets in a key telephone system. The main operating unit and each telephone set includes a pulse transmitting and receiving circuit and a transformer having a core and first and second pairs of opposed windings. The individual windings in the first winding pair are connected to input and output terminals, respectively, of the pulse transmitting and receiving circuit. One terminal of each individual winding in the second winding pair is connected to a transmission line. A DC power source is connected across the other winding terminals in the second winding pair in the main operating unit. In the telephone set, the other winding terminals in the second winding pair are connected with a power supply circuit which provides power to various component circuits in the telephone set. A capacitor is connected across the terminals connected with the power supply circuit in order to prevent the DC power signal from short-circuiting from the DC power source in the main operating unit to the power supply circuit in the telephone set.
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