A power converter controller includes a drive circuit coupled to control switching of a power switch coupled to an energy transfer element and an input of the power converter. An output voltage sensor including first and second pulse sampler circuits is coupled to capture first and second peak voltages, respectively, that are representative of a second peak of a ringing voltage of a feedback signal representative of an output of the power converter. The first pulse sampler circuit is coupled to capture the first peak voltage at a first time in the feedback signal. The second pulse sampler circuit is coupled to capture the second peak voltage at a second time in the feedback signal. The drive circuit is coupled to receive a change signal from the output voltage sensor in response to the first and second peak voltages.