Handheld device and power supply circuit thereof

A handheld device comprising:

• a backlight driving unit;
• and
• a power supply circuit for powering the backlight driving unit, the power supply circuit comprising:
• a power management unit (PMU) comprising an input pin and an output pin;
• a rechargeable battery comprising a positive terminal electrically connected to the input pin of the PMU, and a negative terminal grounded;
• a first electronic switch comprising a first terminal, a second terminal electrically connected to the positive terminal of the rechargeable battery, and an output terminal electrically connected to the backlight driving unit;
• and
• a second electronic switch comprising a first terminal, a second terminal electrically connected to the backlight driving unit, and a third terminal electrically connected to the output pin of the PMU;
• a control unit electrically connected to the first terminals of the first electronic switch and the second electronic switch, the second terminal of the second electronic switch, and the positive terminal of the rechargeable battery;
• and
• wherein in response to a voltage of the second terminal of the second electronic switch being less than a reference voltage of the control unit, the control unit outputs a first control signal to the first terminals of the first electronic switch and the second electronic switch, such that the first electronic switch is turned on and the second electronic switch is turned off, the backlight driving unit is then powered by the rechargeable battery through the first electronic switch;
• and
• wherein in response to the voltage of the second terminal of the second electronic switch being more than the reference voltage of the control unit, the control unit outputs a second control signal to the first terminals of the first electronic switch and the second electronic switch, such that the first electronic switch is turned off and the second electronic switch is turned on, the backlight driving unit is then powered by the output pin of the PMU through the second electronic switch.