Patent ID: 7564212

Claim:
A mobile communication device, comprising: a processing unit; a battery unit connecting to the processing unit to function as a main power source of the processing unit, and supplying the main power to the processing unit by providing a first working current for the processing unit; a solar cell unit connecting to the processing unit to function as a spare power source of the processing unit, receiving and transforming luminance into an analog voltage, and providing a charging current for the battery unit and supplying the spare power to the processing unit by providing a second working current for the processing unit; an analog-to-digital converter connecting to the processing unit and the solar cell unit for converting the analog voltage from the solar cell unit into a digital voltage and transmitting the digital voltage to the processing unit; and an electronic switch circuit connecting to the processing unit and the solar cell unit, wherein the processing unit generates a control signal from the digital voltage depending on the relative size of the first working current and the second working current, and the control signal is used to control the electronic switch circuit to turn the solar cell unit on or off; when the first working current is greater than the second working current, the control signal controls the electronic switch circuit to turn the solar cell unit off; when the solar cell unit is turned on, the solar cell unit provides power for the processing unit; and when the solar cell unit is turned off, the solar cell unit doesn't provide power for the processing unit.