| 摘要 |
PROBLEM TO BE SOLVED: To protect a step-up converter against overcurrent due to short-circuiting on the output side or overloading without inserting any additional element into a current supply path in the step-up converter. SOLUTION: A power supply unit is so constructed that charging/discharging of an inductor (1) is switching controlled to increase direct-current input voltage, and the increased voltage is smoothed through a capacitor (3) to obtain direct-current output voltage. The power supply unit includes: a transistor (2) that is connected between the inductor (1) and the capacitor (3) and exerts rectifying action; an output voltage determination circuit (6) that refers to direct-current input voltage and direct-current output voltage and determines which voltage is higher; and a current control circuit (7) that controls the current passed through the transistor (2) to a predetermined value when it is indicated by the output voltage determination circuit (6) that the direct-current output voltage is lower than the direct-current input voltage. COPYRIGHT: (C)2008,JPO&INPIT
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