| 摘要 |
PURPOSE:To attain the assured protection of a transistor against a short circuit by reducing the limit value of a forward bias current in response to the level of the voltage between the collector and the emitter of a transistor serving as a switching element. CONSTITUTION:A base driving circuit 30 feeds back the collector-emitter voltage VCE of a primary transistor TR12. Then the circuit 30 reduces the limit value IB of a forward bias current when the VCE approximates to the level of the voltage V1 of a DC power supply 10. Thus the collector current IC of the TR12 is limited to a level necessary for detection of an overcurrent. Then an overcurrent detector 18 detects such as short circuit current and supplies a trip signal to an ON/OFF command unit 20. Then the unit 20 delivers an OFF command to turn on an adverse bias TR of the circuit 30. This TR is immediately turned off with supply of an adverse bias current to the TR12. |
