| 摘要 |
<p>A line driver circuit including a protective circuit to prevent excess current destroying it. The line driver circuit comprises a protective transistor (Q,) for limiting the output current of an output-stage emitter-follower transistor (Q3), a detecting means (R4) for detecting the output current of the emitter-follower transistor (Q3), and a pull-up transistor (04) for pulling up the base potential of the protective transistor (Q1) to turn it on. As the output current increases, the detecting means (R4) detects when it reaches a predetermined value to turn on the pull-up transistor(Q4) so that the base potential of the protective transistor (Q,) is pulled up which, in turn, turns on the protective transistor (Q,). As a result the base current of the emitter-follower transistor (Q3) is decreased, so that the emitter-follower transistor (Q3) is protected from being thermally destroyed.</p> |
