A duty cycle estimator determines a duty cycle for controlling a regulated output of an output regulator. The output regulator is responsive to the duty cycle for controlling a transfer of energy between an input source and the regulated output. An error generator compares the regulated output to an output reference to generate an output error. An accumulator determines an accumulated error of the output error over a time period of at least N times a switching period of the output regulator, where N is an integer. A reference generator generates reference levels. A comparator compares the accumulated error to the reference levels such that a single zero is generated, and generates the duty cycle based on the comparing.