A method for controlling a switched tank converter (STC) includes (a) driving a first resonant tank circuit of the STC at a first frequency and with a first fixed on-time, to obtain a first fixed ratio of output voltage of the STC to input voltage of the STC, while the STC is powering a load having a first magnitude and (b) driving the first resonant tank circuit of the STC at a second frequency and with the first fixed on-time, to obtain the first fixed ratio of output voltage of the STC to input voltage of the STC while the STC is powering a load having a second magnitude. The second frequency is smaller than the first frequency, and the second magnitude is smaller than the first magnitude.