48 V-to-1 V Transformerless Stacked Active Bridge Converters with Merged Regulation Stage

Transformerless stacked active bridge (TSAB) converters are hybrid converters derived from switched capacitor converters by addition of small inductors. TSAB converters achieve the highest efficiency around a nominal conversion ratio because of "soft" charging/discharging of all flying capacitors, low rms currents and zero-voltage-switching of power switches. This paper introduces new configurations of TSAB converters with inductive filter as opposed to capacitive filter at the output port, which opens opportunities to merge a regulation stage at the output. The approach is applied to 48 V to 1 V point-of-load (PoL) conversion by merging a 6-to-1 Dickson TSAB with a multi-phase buck converter at the regulation stage, greatly reduced the need for a bulky intermediate bus capacitor. Experimental results are provided for a 48 V-to-1 V, 100 A prototype consisting of a 6-to-1 TSAB operating at 100-125 kHz using 120 nH inductors, and an off-the-shelf four-phase buck regulating stage operating at 500 kHz. The prototype has 91.5% peak efficiency at 25 A and greater than 85% efficiency up to 90 A.