| 摘要 |
PURPOSE:To improve the stability of operation, by increasing the non-conducting time of a switching semiconductor when the input current and voltage exceed a preset level. CONSTITUTION:A control circuit 19 is composed of an input current detector circuit 15, input voltage detector circuit 17, comparator 16, gate timing circuit k8 and gate drive circuit 14. The input current and voltage are detected by the detectors 15, 17 and the level whichever is higher is compared by the comparator 16 with a preset level to feedback to the gate timing circuit 18. When the input current and voltage exceed the reference level, the delay time of a delay circuit 12 is extended, the period of a gate signal is expanded to lower the frequency, then the value of high frequency current is automaticaly reduced to stabilize the high frequency switching action of a thyristor 51 used in the frequency convertor circuit 10. At the same time, the value of input current is reduced below the preset level without regard to the type and size of the pan 8 as load. |
