| 摘要 |
PROBLEM TO BE SOLVED: To prevent the flow of over-current into a switching element, when an input voltage rises abruptly. SOLUTION: When momentary interrupt of an input AC voltage occurs, a comparison means 6 does not generated pulse during such period, because a voltage is not supplied from a rectifying circuit 106 to the comparing means 6. Therefore, a pulse detecting circuit 8 is unable to detect the pulse in this case and outputs a cut-off signal. The pulse detecting circuit 8 delays this cut-off signal for about 20 msec, before it provides the output. Therefore, even if momentary interrupt is recovered, the cut-off signal is output for about 20 msec after such a recovery. When the cut-off signal is input from the pulse detecting circuit 8, a drive pulse generating circuit 125 stops the generation of a drive pulse to turn off a switching element 118. |
