| 摘要 |
PROBLEM TO BE SOLVED: To provide a safe switching power supply unit wherein, even if an input voltage or output voltage varies in a circuit with the especially low inductance of a circuit element, an output current is limited to a constant value, and overcurrent protection is provided with stability without fail. SOLUTION: In the overcurrent protection circuit of the switching power supply unit, an input voltage is turned into rectangular-wave voltage by the on- and off-operation of a switching means, and the rectangular-wave voltage is smoothed by an inductance element 6 and a capacitor 7 to produce an output voltage. In the switching power supply unit, the peak current of currents passed through the switching means, and an overcurrent is limited using the input voltage Vin, output voltage Vout, and voltage in proportion to the on-to-off ratio D of the switching means.
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