A controller includes a feedback sensing circuit that generates a feedback current during a first time interval in a switching period of a power converter based on an output voltage of the power converter and to generate a digital sensing signal indicative of a duration of the first time interval, and a feedback signal generator that determines a magnitude of the feedback current that flows during the first time interval based on a value of the digital sensing signal and to generate a digital feedback signal based on the determined magnitude of the feedback current. The controller adjusts the output voltage of the power converter in response to the digital feedback signal.