The work presented in this thesis focuses on the elimination of step-up step-down mode transition problems that occur in low power dc-dc noninverting buck-boost (NIBB) converters, while also significantly improving power processing efficiency compared to existing state-of-the-art solutions. Near the step-down step-up boundary, the introduced controller enters a low-frequency ripple shaping mode of operation that allows lower switching frequency than in conventional buck or boost modes without paying a penalty of increased inductor current ripple, i.e. higher RMS current. As a result, both switching, and conduction losses are reduced. In addition, multi-level non-inverting buck-boost (ML-NIBB) is presented as a potential alternative to the conventional NIBB. Compared to the conventional architecture, the ML-NIBB converter has the potential to reduce the total volume and increase power processing efficiency. An extended version of the ripple-shaping controller is presented and used to preserve the smooth transition between step-down and step-up mode. The effectiveness of the presented ripple-shaping controllers is demonstrated with two 1.8 V to 5 V input, 3.3 V/10 W experimental prototypes, for both NIBB and ML-NIBB topologies.ii