| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply circuit which attains high power conversion efficiency and a low lower-limit voltage for operation start. SOLUTION: The switching power supply circuit includes: an input terminal; an output terminal from which an output voltage is output; a choke coil and a rectifying device which are connected in series between the input terminal and the output terminal, and to which an input voltage is input and from which the output voltage is output; a voltage step-up switching element of which one end is connected between the choke coil and the rectifying device and the other end is connected to a grounding point; a power supply control circuit, to which the output voltage is input as driving power supply and which controls the voltage step-up switching element and the rectifying device; a transistor connected between the input terminal and the output terminal in parallel with the choke coil and the rectifying device; and a differential amplifier to which a first voltage derived from the input voltage and a second voltage derived from the output voltage are input, makes the transistor conducted when the first voltage is higher than the second voltage, and cuts off the transistor when the first voltage is lower than the second voltage. COPYRIGHT: (C)2006,JPO&NCIPI
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