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A chip harvests power from multiple sources

Posted: 12 Jul 2012     Print Version  Bookmark and Share

Keywords:control circuit  photovoltaic cells  battery-free monitoring systems 

PhD student Saurav Bandyopadhyay and professor Anantha Chandrakasan at MIT have developed a chip that could harness power from natural light, heat and vibrations in the environment and can operate at extremely low power levels.

According to the researchers, the chip could be used in battery-free monitoring systems like biomedical devices, environmental sensors in remote locations and gauges in hard-to-reach spots, among other applications.

"The key here is the circuit that efficiently combines many sources of energy into one," Chandrakasan said. Combining the power from these variable sources requires a sophisticated control system, he added.

Typically each energy source requires its own control circuit to meet its specific requirements. For example, circuits to harvest thermal differences typically produce only 0.02 to 0.15V, while low-power photovoltaic cells can generate 0.2 to 0.7V and vibration-harvesting systems can produce up to 5V.

Until now, the simplest strategy has been simply to switch between the highest energy generation source. However, in order to avoid any wastage of energy being delivered from any of the sources, the new approach combines energy from multiple sources by switching rapidly between them.

The system uses an dual-path architecture allowing energy to be used directly or to be stored and the switch matrix and the control circuits are implemented in a 0.35µm CMOS process.

The chip uses a single time-shared inductor, a crucial component to support the multiple converters needed in this design, rather than separate ones for each source.

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

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