| 摘要 |
An external power source control system for a portable telephone includes: a regulator 5 connected at an input thereof to a battery power source 1 or an external power source 2 and outputting a power supply voltage; a one-shot pulse generating circuit 6 generating a one-shot pulse when the external power source 2 is connected to the portable telephone; a reset circuit 7 outputting a reset signal when the power supply voltage reaches a predetermined threshold level; and a controller maintaining an output of the power supply voltage from said regulator 5 , based on the one-shot pulse, and canceling the maintenance of the output of the power supply voltage from said regulator 5 , based on a predetermined instruction indicating that the power is not necessary.
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