| 摘要 |
PURPOSE:To eliminate a malfunction caused by an electrical noise and to limit an excess main current at high speed to cut it off nearly till zero. CONSTITUTION:A main current is adjusted by IGBT1 to which a load is connected. A part of the main current is shunted to IGBT2. The shunted current is converted to voltage between both terminal of a resistance 3 with the current flowing through a resistance 3. When the main current excessively flows owing to short-circuit, etc., this voltage exceeds a prescribed value and a transistor 5 and a thyristor 7 come into a conductive state. As a result, a voltage between the gate G and the emitter E of IGBT is made to drop so as to cut off the main current. Since the transistor responds quickly, the excessive flow of the main current is previously prevented, and since resistance at the time of conduction is lower in the thyristor, the main current is cut off to zero. |
