| 摘要 |
The invention relates to a polarity identification circuit for use in telephone systems. The polarity identification circuit delivers an output signal which indicates the polarity of a voltage difference between two nodes of a circuit. In one version of the invention, the circuit has its own power supply connection (+5V), i.e. which is different and independent from the connecting terminals (a, b), a resistance (R4) and a switching element (T3). The switching element has, for its part, a control terminal and two connections of a load line. The load line of the switching element is connected into the current path between the power supply connection and a connecting terminal, and the control terminal is connected via the resistance to a connecting terminal. The output signal (RP) can then be picked up at a connection of the load line of the current element. |
