| 摘要 |
A constant voltage regulator and registers R 1 and R 2 generate a reference voltage with at least one of voltages supplied from a battery and an AC adaptor. The reference voltage is supplied to a first input terminal of a comparator. An input voltage supplied from the AC adaptor and divided by registers R 3 and R 4 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, an FET switch SW 1 is turned on and power is supplied from the AC adaptor side. When the reference voltage is higher than the input voltage, an FET switch SW 2 is turned on and power is supplied from the battery side.
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