| 摘要 |
PURPOSE:To accurately protect a transistor against an excess current by detecting the collector voltage or base voltage of a transistor at conducting time to detect the shortcircuit of a load, thereby interrupting the transistor. CONSTITUTION:When a base current supply circuit 7 or a surge absorber becomes defective so as to lose the surge absorbing function, the collector voltages of transistors TR1, TR2 of a transistor chopper circuit 5 at the conducting time abnormally increase. The excess voltage of this collector voltage is detected by an overvoltage detector 13, a thyristor SCR is fired to be conducted, and a transistor TR4 remains nonconductive state, and the transistors TR1, TR2 are interrupted. |
