A harvester chip that can bypass storage elements

Researchers from the Massachusetts Institute of Technology say they have come up with an integrated circuit design that combines the energy from solar, thermal, and vibration sources. Moreover, unlike most energy harvesting chips, the new device can send harvested power directly to a load instead of first using it to charge a storage device, typically a battery.

The dual-path architecture for energy harvesting that makes this possible has a peak efficiency improvement of 11 to 13% over the traditional two-stage approach, researchers say. The system consists of a reconfigurable multi-input, multi-output switch matrix that combines energy from three distinct energy-harvesting sources–photovoltaic, thermoelectric, and piezoelectric. The IC can handle input voltages from 20 mV to 5 V and is capable of extracting maximum power from individual harvesters all at the same time utilizing a single inductor.

The chip even implements maximum power point tracking for the photovoltaic harvester using a special power monitor. Researchers say it has a peak tracking efficiency of 96%. The peak efficiencies achieved with inductor sharing are 83%, 58%, and 79% for photovoltaic boost, thermoelectric boost, and piezoelectric buck-boost converters, respectively. The switch matrix and the control circuits are implemented on a 0.35-micron CMOS process.

So far, most efforts to harness multiple energy sources have simply switched among them, taking advantage of whichever source is generating the most energy at a given moment, says MIT doctoral student Saurav Bandyopadhyay, but that can waste the energy being delivered by the other sources. “Instead of that, we extract power from all the sources,” he says. The approach combines energy from multiple sources by switching rapidly between them.

The energy-combining circuit is described in a paper being published this summer in the IEEE Journal of Solid-State Circuits:

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