| 摘要 |
PURPOSE:To prevent the breakage of the thyristor by conductig the thyristor when a forward voltage is applied again thereto in case where the reverse voltage period is shorter than the period necessary to turn off the entire thyristor. CONSTITUTION:The reverse voltage single D from the thyristor 1 is applied through a control protector 7 to a timer 8, which counts the interval between the on pulse and the off pulse proportional to the frequency of the voltage of main circuit, and the counted value is inputted to a comparator 9. On the other hand, a reference signal pulse B corresponding to the voltage capable of normally operating a reverse voltage detecting circuit is inputted to the comparator 9. The input signal A is compared with the reference signal pulse B so that the signal A is higher than the signal B, the signal D is used for the control and the protection. When the signal A is lower than the signal B, the signal D is locked to eliminate the erroneous control and protection, and to prevent the breakage of the thyristor by donducting the thyristor. |
