High-frequency isolated DC-DC converters are gaining momentum in applications where the demand of isolation matches with that one of compact and light equipment. A seminal topology, constituted by two bridges operating at high frequency and coupled by a transformer, has emerged as an attractive solution that fulfills the above-mentioned demands. The two most popular versions of such a topology are the Single Active Bridge (SAB) and Dual Active Bridge (DAB) converters. This paper deals with the characteristics of the two converters that are helpful in designing their input and output filters, transistors and diodes. Explicitly, the peak-to-peak ripple and the rms value of the alternate component of current at the converter input and output as well as the peak, average and rms values of current through transistors and diodes of the converter are calculated. All the quantities are expressed as a function of the load current and voltage along the operating range, by referring to an application requiring a unidirectional power flow of buck type. A comparative analysis of the design characteristics of the two converters closes the paper.