| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a switching power supply unit having a simple configuration and capable of properly controlling an output voltage. Ž<P>SOLUTION: The switching power supply unit includes: a switching circuit; a control means for switching-controlling the switching circuit by a PWM system; and a detecting means for detecting an output voltage. In the switching power supply unit, the control means is a means for changing a duty ratio in the PWM so that the output voltage detected by the detecting means may approximate to a target voltage, and changes the duty ratio in the tendency in which the degree of increase/decrease in the duty ratio is smaller as the power supply target has higher load and the degree of increase/decrease in the duty ratio is larger as the power supply target has lower load. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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