In this chapter, the flyback (isolated buck/boost) topology is used to simplify the twostage front-end design to a single isolated PFC conversion stage. This is conceptually illustrated in Fig. 3.1, where it is assumed unity power factor is present at the line input. The two keys to the process of simplifying the two-stage approach are the incorporation of transformer isolation in the PFC converter and the subsequent movement of the bulk capacitor from the primary to the secondary. The result of this is that the input line current’s second harmonic (at 120 Hz) is processed by the isolation transformer and appears as voltage ripple on the output DC bus. Therefore, in effect, the post-regulators in the DC distributed power system take the functional place of the second-stage DC/DC converter in the two-stage front-end approach.