| 摘要 |
PURPOSE:To prevent a chopper element from being damaged due to an overcurrent by providing instantaneous current detecting means and overcurrent level setting means and forcibly turning OFF the chopper element. CONSTITUTION:A voltage comparator 21 compares the instantaneous value (f) of the secondary current detected by a DC current transformer 8 with the overcurrent level (e) set by a setter 20. When both coincides, a monostable multivibrator 22 is driven at every time to generate a pulse output (g) having a continuous period (t). Since this output (g) closes an AND gate 23 only during a low level period, the output pulse waveform (c) of a voltage detector 13 is intermittently interrupted and applied to a chopper 7, and the chopper 7 is turned to OFF. In this manner, since the instantaneous value of the secondary current idc does not exceed the overcurrent level, there exists no possibility that the chopper 7 is damaged. |
