A resonant switching converter comprises a resonant tank having a resonant frequency; a synchronous rectifier coupled to the resonant tank, the synchronous rectifier drawing power from the resonant tank for forming an output voltage; and a controller coupled to the synchronous rectifier for controlling switching of the synchronous rectifier using frequency modulation. The controller operates in a first mode in which the switching of the synchronous rectifier is performed above the resonant frequency of the resonant tank. The first mode employs a duty cycle for the synchronous rectifier. In addition, the controller operates in a second mode in which the switching of the synchronous rectifier is performed below the resonant frequency and the duty cycle of the synchronous rectifier in the second mode is reduced from that of the first mode.