The protection circuit for a power source of an electronic device capable of providing a certain range of current values to a peripheral unit comprising a power storage unit. The protection circuit comprises a first and second charging paths and a voltage detector. The voltage detector switches the first charging path to turn on the first switch, when the voltage value of the power storage unit 30 is lower than the threshold voltage, the power source can charge the power storage unit by the first switch, wherein the current limiting device limits the current value of first charging path to lower than a predetermined. The voltage detector switches the first charging path to breakup the second switch and the voltage detector switches to the first charging path to turn on the first switch.