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 is coupled to the control switch, and controls operation of the control switch between an ON state and an OFF state such that the control switch starts to operate in the 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.