| 摘要 |
PROBLEM TO BE SOLVED: To suppress decrease in a switching frequency of a switching power source apparatus at the time of a heavy load, and to reduce the number of windings of a transformer. SOLUTION: The switching power source apparatus comprises a zero current detector (13) for outputting a zero current detection signal VZCD, when no current flows in a transformer (2), an OFF time detector (14) for detecting OFF time of a MOSFET (3), and a frequency-clamp circuit (15) for outputting the zero current detection signal VZCD from a comparator (14) irrespective of the output of the detector (13), when the OFF time detected by the detector (14) becomes a maximum OFF time or more, which is specified by a reference voltage of a reference power source (18). The power source apparatus further comprises a control circuit (8) for imparting an ON signal VG to a gate terminal of the MOSFET (3), when the detector (13) or the frequency clamp circuit (15) outputs the zero current detection signal VZCD.
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