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

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Abstract
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.

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