| 摘要 |
A constant voltage regulator and registers R1 and R2 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 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, an FET switch SW1 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 SW2 is turned on and power is supplied from the battery side.
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