Systems, apparatuses, and techniques for pulse width modulation (PWM) are described. A described system includes a circuit that contains an inductor and a transistor that controls current through the inductor based on a PWM signal to produce an output; and a controller to provide the PWM signal, which includes PWM cycles that include on-durations and off-durations. The controller can receive a first signal indicating an input voltage that is applied to the inductor, receive a second signal indicating a current through the inductor, use an on-duration parameter value to control the on-duration, determine a maximum off-duration of the off-durations corresponding to the PWM cycles occurring within a first voltage cycle, the first voltage cycle being defined between two consecutive zero-crossing events as indicated by the first signal, and adjust the on-duration parameter value for a second, subsequent voltage cycle based on the maximum off-duration to regulate the output voltage.