| 摘要 |
PURPOSE:To eliminate the damage of a thyristor by limiting the allowable range of applying a gate pulse so as not to apply the gate pulse when a reverse voltage is applied to the thyristor. CONSTITUTION:The gate pulse generation enabling range of an R<+> element is limited to 30-210 deg. of controlling angle by a circuit of a transistor 23 and further to when a gate pulse to an S<+> element is not produced by a signal from an NAND logic element 34. The phase control signal is compared at a potential with the phase power source voltage by the transistor 22, thereby controlling the firing angle of the R<+> element. Then, the gate pulse generation enabling range of the S<+> element is limited to 0-150 deg. of controlling angle by the circuits of transistors 25, 26. |
