On the selection of optimal turns ratio for transformers in isolated DC/DC boost full bridge converter

This document aims to describe a rigorous approach to correctly select the optimal turns ratio for a transformer involved in an isolated DC/DC boost full bridge converter realization, considering the input/output voltage ranges, the modulation scheme adopted and the efficiency constraints. The topological structure is first introduced, outlining the hardware components used. The step-down (or Buck) and step-up (or Boost) modulations are then briefly discussed, focusing mainly on the input/output relations in both operative modes. These equations are assumed as the starting point for the core discussion of this paper, about the selection of the transformer turns ratio. The problem is approached independently first in Buck mode, then in Boost mode. In particular, the ideal situation is first considered, introducing then a corrective factor for taking into account the dissipative losses due to parasitical effects. Finally, the partial results obtained are merged in a conclusive phase, where a single turns ratio have to be chosen due to the bi-directionality of the converter. The methodology proposed has been successfully tested in SABER simulative environment, before the realization phase; measurements on the real converter evidence the correctness of the proposed approach, arising as a general procedure to select a transformer involved in DC/DC conversion strategy, in the context of a boost full bridge topology.