Rossi, Kimms & McDowell LLP
Switching power supply device and switching power supply control circuit
The invention provides a switching power supply device which can detect a light load state on a pulse-by-pulse basis without worsening power efficiency. In a synchronous control circuit, for each timing of the turning-on of main switching elements, the delay time Tdif of the conduction timing of internal diodes Ds determined according to the magnitude of the load LD is detected by a comparator, a reference time pulse Tsrs having a prescribed time width is generated by a load judgment circuit, and the logical product of the two is generated by an AND circuit. By this means, the load is regarded as being a light load when the delay time Tdif is longer than the reference time pulse Tsrs, and the synchronous rectification MOSFETs Qs are not turned on.
Fuji Electric Co., Ltd.
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Jian Koji
Chen Sonobe