A charging circuit includes a transistor, a current regulating resistor, a field effect transistor (FET) and a main controller. The transistor includes an emitter, a base and a collector, the FET includes a source, a gate and a drain. The emitter is connected to the battery charger; the drain is connected to the battery. The main controller includes a current control unit, a charge control unit and a voltage detection unit. The current control unit transmits current signals to the base of the transistor to turn on the transistor and regulate the current values of the collector, the voltage detection unit detects the voltage of the battery and controls the charge control unit according to detection result, and the charge control unit sends a command signal to the gate to switch the FET on or off.