Comparison of Low-Power Single-Stage Boost Rectifiers for Sub-Milliwatt Electromagnetic Energy Harvesters

Energy harvesting could provide power-autonomy to many important embedded sensing application areas. However, the available envelope often limits the power output, and also voltage levels. This paper presents the implementation of an enabling technology for space-restricted energy harvesting: Four highly efficient and fully autonomous power conditioning circuits are presented that are able to operate at deep-sub-milliwatt input power at less than 1 V-pk AC input, and provide a regulated output voltage. The four complete systems, implemented using discrete components, include the power converters, the corresponding ancillary circuits with sub-10 mu W consumption, start-up circuit, and an ultra-low-power shunt regulator with under-voltage lockout for the management of the accumulated energy. The systems differ in their power converter topology; all are boost rectifier variants that rectify and boost the generator's output in a single stage, that are selected to enable direct comparison between polarity-dependent and -independent, as well as between full-wave and half-wave power converter systems. Experimental results are derived over a range of 200-1200 mu W harvester output power, the system being powered solely by the harvester. Experimental results show overall conversion efficiency, accounting for the quiescent power consumption, as high as 82% at 650 mu W input, which remains in the 65-70% range even at 200 mu W input for the half-wave variant. Harvester utilisation of over 90% is demonstrated in the sub-milliwatt range using full-wave topologies. For the evaluated generator, the full-wave, polarity-dependent boost rectifier offers the best overall system effectiveness, achieving up to 73% of the maximum extractable power.