A phase shift full bridge (PSFB) converter includes: an isolation transformer; a full-bridge having a first pair of switch devices connected in series at a first node coupled to a first terminal of the primary side of the isolation transformer, and a second pair of switch devices connected in series at a second node coupled to a second terminal of the primary side of the isolation transformer; a rectifier coupled to the secondary side of the isolation transformer; and a controller for switching the first and second pairs of switch devices out of phase with each other. Under nominal input voltage conditions for the PSFB, the controller switches the first and second pairs of switch devices at a nominal switching frequency. Under reduced input voltage conditions for the PSFB, the controller switches the first and second pairs of switch devices at a frequency lower than the nominal switching frequency.