| 摘要 |
PURPOSE:To absorb surge currents effectively even when abnormal high voltage is applied, and to prevent the breakdown of an input transistor by forming an insulated gate field-effect transistor, a gate thereof is connected to an external input terminal and a drain thereof is connected to the external input terminal through a protective resistor. CONSTITUTION:A field transistor 17a takes constitution in which a gate is connected to an external input wiring 1 and a drain is connected to a protective resistor 8 in a distributed constant circuit manner. When the gate of the field transistor 17a directly receives abnormal high voltage higher than the threshold voltage of the gate, the transistor 17a is conducted regardless of the drain voltage of the transistor, thus directly bypassing one part of surge currents to a grounding 13 from the whole region of the protective resistor 8. Accordingly, the breakdown of an input transistor can be prevented. |
