A controller for a DC-DC converter that includes an inductor. The DC-DC converter has three phases of operation: a first phase, in which an input voltage charges the inductor; a second phase, in which the inductor discharges to a load; and a third phase, in which the inductor is disconnected from the load and in which the input voltage does not charge the inductor. The controller is configured to set a control-factor based on the input voltage of the DC-DC converter, and set the duration of the third phase based on the control-factor and the sum of the duration of the first phase and the second phase.