| 摘要 |
PROBLEM TO BE SOLVED: To provide a power supply device whose power supply efficiency in a power saving operation is taken into consideration. SOLUTION: In addition to a 1st switching circuit 5 which operates in a steady operation, a 2nd switching circuit 9 which operates in a power saving operation only is provided. When the power saving operation is started, a voltage between both the terminals of a detection resistor R1 is reduced to a value lower than the internal reference voltage, and the operation of the 1st switching circuit 5 is stopped via a comparison circuit 6 and a change-over circuit 8. At the same time, in order to make the 2nd switching circuit 9 operate, a control circuit 2 makes a 2nd switching transistor TR2 operate. With this operation, two switching circuits are changed over, and optimum power supply efficiency in the respective operation states can be achieved.
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