| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching control circuit which stops switching in an area where a phase angle of an ac power supply is low to allow less flow of current to prevent malfunction in return operation after brownout detection. SOLUTION: A comparator 22 gives a high-level output signal 23 to a timer 24 when detecting that a divided voltage from a voltage Vm has dropped to a voltage equal to or lower than a first reference voltage 21. The timer 24 inputs its output signal 25 to a D terminal of a DFF 37. A comparator 32 turns its output signal 33 to a high-level signal when detecting that a voltage Vin(1) has become equal to or lower than a given voltage through the divided voltage from the voltage Vm. The high-level output signal 33 and a clock signal 35 are ANDed by an AND circuit 34, and an output signal 36 from the AND circuit 34 is input to a clock terminal of the DFF 37. The output signal 25 from the timer 24 changes the state of a Q output signal from the DFF 37 at a rising edge of the clock signal 35 only when the output signal 33 from the comparator 32 is high. The Q output signal controls a pulse signal 27 passing through a NOR circuit 26, that is, continuation/stoppage of switching operation. COPYRIGHT: (C)2009,JPO&INPIT
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