Electronic devices receive power in a variety of ways. For example, consumer electronic devices may receive power from a wall outlet (e.g., mains) or from various portable sources (e.g., batteries, renewable energy sources, generators). Battery operated devices have an operational time that is dependent upon battery capacity and average current draw. Manufactures of battery powered devices may strive to reduce average battery current of their products in order to offer longer device use between battery replacement or between charge operations. In some examples, manufacturers of mains powered devices may strive to increase power efficiency of their products in order to minimize thermal loads and/or to maximize the performance per watt of power consumed.
In some electronic devices, an input voltage supply (e.g., battery input, rectified mains supply, intermediate DC supply) may be converted to a different voltage by various voltage conversion circuits. Switch-mode power supplies have gained popularity as voltage conversion circuits due to their high efficiency and therefore are often used in various electronic devices.
Switch-mode power supplies convert voltages using switching devices that turn on with very low resistance and turn off with very high resistance. Switch-mode power supplies may charge an output inductor during a period of time and may release part or all of the inductor energy during a subsequent period of time. The output energy may be delivered to a bank of output capacitors, which provide the filtering to produce a DC output voltage. In buck-derived switch-mode power supplies, the output voltage, in a steady state, may be approximately the input voltage times a duty cycle, where the duty cycle is the duration of the on-time of a pass switch divided by the total on-time and off-time of the pass switch for one switching cycle.