This paper presents an integrated maximum power point tracking system for use with a thermophotovoltaic portable power generator. The design, implemented in 0.35-mu m CMOS technology, consists of a low-power control stage and a dc-dc boost power stage with soft-switching capability. With a nominal input voltage of 1 V, and an output voltage of 4 V, we demonstrate a peak conversion efficiency under nominal conditions of over 94% (overall peak efficiency over 95%), at a power level of 300 mW. The control stage uses lossless current sensing together with a custom low-power time-based analogto- digital converter to minimize control losses. The converter employs a fully integrated digital implementation of a peak power-tracking algorithm, and achieves a measured tracking efficiency above 98%. A detailed study of achievable efficiency versus inductor size is also presented, with the calculated and measured results.