| 摘要 |
PURPOSE:To enable to absorb overvoltage into a surge absorbing circuit by a method wherein a forward direction overvoltage detection circuit is provided on each arm of a transformer respectively and the thyristor of each arm is turned on. CONSTITUTION:A DC-side surge absorbing circuit 14 is rovided in parallel with a load 12 and at the same time, forward direction overvoltage detecting circuit 15-20 are provided on a thydristor arms U-Z respectively. When the polarity of the overvoltage is a backward overvoltage to thyristors U and Y, it is turned to forward direction overvoltage to thyristors V and X without fail. Accordingly, the forward overvoltage of the thyristors V and X is detected by forward direction overvoltage detecting circuits 16 and 18, the thysrisors V and X are turned on by a gate pulse generating circuit 11, andthe oervoltage is absorbed by a surge absorbing circuit 14. |
