| 摘要 |
PURPOSE:To prevent failure of an SCR element by detecting a reverse voltage applied to the SCR and conducting the SCR by a gate signal when the reverse voltage time is shorter than required turn-off time of the element to reduce the internal loss at a break-through time. CONSTITUTION:A current detector 11 of a current flowing through a main SCR 3 of a chopper 2 consists of a resistor 12 inserted in series with the SCR3 and an am plifier 13 for detecting a voltage drop caused at the resistor 12. A reverse voltage voltage signal generator 14 receives a signal representing the current of the SCR3 applied from the amplifier 13 and produces a ''0'' signal indicating the application of predetermined reverse voltage thereto when the value of the current flowing in reverse direction with respect to the SCR3 becomes higher than predetermined value. The output of the generator 14 is applied to one input terminal of an AND gate 15 and through a time limiting element 16 to the other input terminal of the AND gate 15. In this manner it can prevent the failure of the element to contrive the improvement in the reliability of the thyristor. |
