| 摘要 |
<p>A fault detector and current limiter for use in E & M telephone trunk circuits includes a normally nonconductive controlled conduction device, which in response to an off-hook signal, is rendered conductive so as to supply a relatively negative potential to an output lead indicative of an off-hook condition of a subscriber's telephone. A current limiter coupled to the normally nonconductive controlled conduction device and to the output lead inhibits the conductivity of the normally nonconductive controlled conduction device in the event an adverse condition occurs on the output lead, such as a short to ground. In response to an on-hook signal, the normally nonconductive controlled conduction device is rendered nonconductive and a normally conductive controlled conduction device is rendered conductive so that a ground potential indicative of an on-hook condition at the subscriber's telephone is applied to the output lead. In the event an abnormal or adverse condition occurs on the output lead, such as a short to battery, another current limiter coupled to the normally conductive controlled conduction device and to the output lead limits the conductivity of the normally conductive controlled conduction device so that the current flowing on the output lead is limited to a safe value.</p> |
