| 摘要 |
<P>PROBLEM TO BE SOLVED: To improve the efficiency of a device by reducing a conduction loss of a switching element which is connected to the primary side of a transformer 3 in series thereto in a switching power supply device 100. Ž<P>SOLUTION: A primary winding 3a of the transformer 3 includes a plurality of tap outputs, MOSFETs 4a, 4b and 4c whose withstand voltages are optimally selected are connected to the tap outputs, respectively, one of the plurality of MOSFETs 4a, 4b and 4c whose duty ratio most approaches 50% is selected and PWM-controlled, and also tap switching is simultaneously performed. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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