| 摘要 |
PURPOSE:To rapidly suppress a DC shortcircuit current by constructing to drive a control circuit at the time of causing a DC shortcircuit to decrease the base current of a power transistor. CONSTITUTION:A commutation failure occurs in a power inverter circuit 4, and a DC shortcircuiting current tends to flow to a negative terminal side of an electrolytic condenser 6 as shown. At this time, the secondary current of a current transformer 25 increases, a voltage between the base and the emitter of a power transistor 21 rises, and the transistor becomes conductive over the set value of a Zener diode 23. Thus, a thyristor 22 is fired, and most base current of large value of the transistor 21 is bypassed to the emitter side through a light emitting diode 28 and the thyristor 22 and decreased. In this manner, the collector current of the transistor 21 is instantaneously decreases, and the DC shortcircuiting current is suppressed. |
