| 摘要 |
PROBLEM TO BE SOLVED: To provide a power source circuit that prevents reduction in a power voltage upon backing up, and allows a large-capacity capacitor to store many electric charges.SOLUTION: A power source circuit comprises: a power source terminal 11 to which a first voltage V1 is externally supplied; a step-down circuit 21a that has an input node connected to the power source terminal 11 via a diode D1, and outputs a second voltage V2a from an output node; a step-up circuit 24 that raises the second voltage V2a to thereby generate a third voltage V3; a capacitor C that is charged by the third voltage V3; and a switch circuit SW that connects the capacitor C and the input node of the step-down circuit 21a in response to a falling of the first voltage V1 to less than a prescribed value. According to the present invention, a charging voltage of the capacitor may be arbitrary, which in turn allows reduction in a power voltage at a time of backing up from being prevented, and allows the capacitor to store many electric charges. |
