Power management circuit and electronic device using the same

An electronic device, comprising:

• a first rechargeable battery;
• a solar cell mounted on the electronic device and configured for receiving ambient light beams and transform received light beams into DC voltage;
• a second rechargeable battery charged by the solar cell;
• and
• a power management circuit, comprising:
• a control module;
• a direct current/direct current (DC/DC) module connected between the solar cell and the control module, and configured for converting the DC power generated by the solar cell from one voltage level to another, and activating the control module when the electronic device runs out of power to turn off, and maintaining the activation of the control module when the electronic device is powered by the first rechargeable battery or the second rechargeable battery;
• a switch controlled by the control module and connected between the second rechargeable battery and the DC/DC module, wherein the switch is turned on by the control module after the control module is activated, causing the DC power from the DC/DC module to charge the second rechargeable battery;
• and
• a power supply switching module controlled by the control module to select the second rechargeable battery to power the electronic device if the voltage level of the first rechargeable battery is lower than that of the second rechargeable battery.