PURPOSE: To facilitate high frequency operation without increasing switching loss during turning-off operation by using a gate turn-off thyristor as a switching element, and using a natural commutating circuit system and a forcible turning- off circuit in common for it.
CONSTITUTION: A capacitor 4 for commutation is connected in series to a reactor 3 as a load, a reactor 5 for power-factor improvement is connected in parallel to it, and a gate turn-off thyristor GTO11 connected to them reversely in parallel, and a diode 7 for commutation are connected in series. When a pulse is inputted to a transformer 17 to turn on the GTO11, an oscillation current by those reactors and capacitor flows. The oscillation current is reversed at some point in time and flows from the cathode of the GTO11 to the gate and the diode 14 by the counter electromotive force of a reactor 12, forcing the GTO11 to turn off. This current decreases with the counter electromotive force of the reactor 12. A reactor 13 is inserted in series to the GTO11 to inhibit the recovery current of the GTO11. Thus, high frequency operation is facilitated without requiring a gate circuit power source.
TOMITA SHIGEO
KOGA KENJI
HITACHI HARAMACHI DENSHI KOGYO