| 摘要 |
The circuit limits current and dissipates excess power to avoid damage to exchange circuits. The power limiting device for a telephone circuit comprises diodes (Z) mounted head to tail on each wire (F1, F2) of the telephone supply cable pair. The device is mounted before connection of any private client equipment, and is preferably fitted at the telephone exchange. The global threshold voltage of the diodes (Z) is chosen in order to obtain a required power dissipation. In alternative circuits, pairs of diodes mounted head to tail may then be connected in parallel for each of the wires of the telephone cable, forming a diode bridge. In addition to the current limiting diodes there may also be an impedance correcting circuit.
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