48V to 1V Active-Clamp Stacked Direct Forward Converter

This paper presents a 4S V-to-1 V stacked direct forward (SDF) dc-dc converter consisting of four 12 V-to-1 V direct forward (DF) modules connected in input-series output-parallel (ISOP) configuration. In each DF module, there is no secondary-side filter inductor, and a single-ended forward transformer is driven at a high duty cycle to reduce the switch root-mean-square currents. An active clamp is employed on the primary side to reset the transformer, limit the switch voltage stress, and facilitate zero voltage switching. The approach is verified by simulation results on a 12 V-to-1V, 50A, 200kHz prototype module using GaN devices and a planar transformer, and having a peak predicted efficiency of 93.4% and the full-load predicted efficiency of 89.3%. Experimental results are presented for a 12 V-to-1 V DF prototype.