Ultralow Power, Fully Autonomous Boost Rectifier for Electromagnetic Energy Harvesters

In this paper, a complete power conditioning system for a vibration energy harvester is presented that operates at ultralow power levels. The power conditioning system, implemented with discrete components, is self-starting and fully autonomous, and based upon a full-wave boost rectifier topology. The design utilizes the stray inductance of the harvester's coil, eliminating the need for separate inductors, and employs open-loop control that reduces the quiescent power overhead to just 21 μW, while still extracting 84% of the maximum available power from the harvester. The design of the subsystems, including self-start circuitry, is described in detail, and it is shown that careful active device selection is required to minimize losses. It is experimentally demonstrated that the power converter achieves conversion efficiencies of up to 76% at submilliwatt power levels, including quiescent losses. The overall system efficiency peaks at 65% at 0.9 mW, while still achieving 51% at 200 μW. The ability of this system to operate efficiently at ultralow average power levels opens up new possibilities to further miniaturize vibration harvesters and deploy them into environments with lower vibration levels than is currently possible.