An energy harvesting device harvests energy from an energy source, and includes an inductor and a control switch coupled in series, and a control module. The series connection of the inductor and the control switch is adapted to be coupled to the energy source in parallel or in series. The control module controls the control switch such that the control switch starts to operate in an ON state for a predetermined time period from a transition time point during each predetermined cycle starting from a start time point, and such that a time difference between the transition time point and the start time point is variable. The control module obtains an output power of the energy source, and adjusts the time difference such that the output power of the energy source is increased. |