| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a power circuit which can efficiently supply constant voltage by selectively operating a step-up circuit and a step-down circuit, according to the magnitude of power voltage. <P>SOLUTION: In case that a USB power source 13 inputs the voltage of 5(V) and an enable switch 26 is ON, the first to third digital transistors 16-18, an n-channel MOSFET 20, and a voltage detector 60 control the step-up circuit 40 and the step-down circuit 50 being transforming circuits and make only the step-down circuit 50 function. On the other hand, in case that a battery 14 inputs the voltage of 1.8(V) and the enable switch 26 is ON, these elements so control the transforming circuits as to make only the step-down circuit 40 function. In either case, a power circuit 10 outputs constant voltage of 3.3(V) from an output terminal 24. <P>COPYRIGHT: (C)2006,JPO&NCIPI</p> |
