The design techniques of high-efficiency non-insulated step-up converters were upgraded on the basis of a comprehensive model of power losses, also including several feeble effects whose contribution, although overshadowed at large power by conduction and switching losses, is relevant in the low-power regime and at the maximum power point. The thorough loss analysis was used as a basis to design state-of-art high-boost-ratio three levels neutral-point-clamped dc–dc converters, whose experimental efficiency showed an outstanding agreement with theoretical predictions in a wide range of operating conditions.