| 摘要 |
PROBLEM TO BE SOLVED: To restrain effectively lightning surge current from entering a communication line by dropping the voltage of a resistive element inserted in series with a transmission line for fluctuating bias voltage between the source and the gate of a field effect transistor. SOLUTION: Bias voltage VSG occurs between the source and the gate of a field effect transistor 3 when a resistive element R10 is inserted in series with a transmission line. Fluctuations in voltage VSG caused by current I11 in ordinary communication is roughly 1 V or less, so that it has little effect on direct current running at the time of ordinary communication. On the other hand, if excessive current (generally, 1 A or more) I11 passes such that causes a fuse break or breakdown of a communications equipment, like lightning surge current, the voltage VSG drops by several volts or more, so that the current running from a drain to a source is restrained. It is thus possible to restrain lightning surge current effectively.
|
