Devices, circuits, and methods generate a substantially constant output voltage. A power storage element generates a DC output voltage from an input voltage. The output is sampled to generate a feedback signal. An error amplifier generates an error signal from the feedback signal and a reference voltage. A ramp generator generates a ramp signal from the error signal. A comparator generates a pulse signal by comparing the ramp signal to a threshold voltage. The pulse signal is used to control a power switch, which switches the power storage element on and off. The pulse signal is generated such that, if the input voltage changes within a certain range, a width of its pulses changes so as to maintain the output voltage substantially constant.