This paper presents a transformer-isolated high step-down dc-dc converter based on a stacked active bridge (SAB) configuration. The isolated SAB (iSAB) converter consists of series-stacked inverter modules and parallel-connected rectifier modules. To achieve galvanic isolation, transformer are inserted between the inverters and the rectifier bridges. The nominal step-down conversion ratio is determined by the number of inverter modules and the turns ratio of the transformer. In order to reduce the footprint of the magnetic components, the transformers are coupled on a single core, and the series inductances are realized as controllable leakage inductances within the same magnetic structure using a novel custom core and planar winding arrangement, a solution unique to the iSAB configuration. The approach is verified by experimental results on a 400-to-48 V, 3 kW, 400 kHz iSAB prototype using GaN devices and having 96.7% peak efficiency.
