| 摘要 |
<p>A portable apparatus (e.g. camcorder) having a first power supply terminal 15 connected to an AC adaptor 12 and a second power supply terminal 14 connected to a battery 11. The apparatus comprises switching devices FETSW1,FETSW2 connected to the first and second power supply terminals, having a constant voltage regulator 21 and registers R1 and R2 to generate a reference voltage with at least one of voltages supplied from the battery and the AC adaptor. The reference voltage is supplied to a first input terminal of a comparator 22. An input voltage supplied from the AC adaptor and divided by registers R3 and R4 is supplied to a second input terminal of the comparator. The comparator compares the reference voltage with the input voltage. When the reference voltage is lower than the input voltage, FETSW1 is turned on and power is supplied from the AC adaptor side. When the reference voltage is higher than the input voltage, FETSW2 is turned on and power is supplied from the battery side.</p> |
