Researchers at the Massachusetts Institute of Technology (MIT) in the US have developed an ultralow-power converter chip that captures more than 80% of energy. What is more, the chip assumes additional functions. It can use a solar cell to either charge a battery or directly power a device.
“The ultralow-power circuit can interface with a solar cell and provide a regulated output voltage supply to power ultralow-power sensors and charge a battery with any excess power that is not required by the load,” says Dina Reda El-Damak, an MIT graduate student in electrical engineering and computer science and first author of the corresponding paper. “It can use the battery to power the device directly when power is not available from the input.”
The chip integrates DC-DC converters along with the necessary control circuits to regulate the input, the output and battery protection during charging and discharging. An integrated startup block allows the system to boot up when the output is initially not regulated.
“The key innovation about the chip is that it can operate very efficiently with very limited input power that ranges from 10 nanowatt to one mircowatt,” El-Damak says. The efficiency drops as the available input power decreases, because the chip itself needs a bare minimum amount of power to operate. “In this work, we were able to reduce this amount of power required by the chip itself without compromising the tasks performed by the chip.”
Her team’s chip achieved efficiencies of up to 80% by operating asynchronously — “only clocking the circuits on demand and shutting down when all the power transfer is done.”
The invention out of MIT could help advance the “Internet of things,” where sensors collect information and send data to other “things” or a server, ideally without requiring battery changes or frequent recharging.
El-Damak says the chip could, for instance, power devices like implanted and wearable sensors that wake up to gather information, transmit the data wirelessly and then go into sleep mode again. “This allows us to deploy systems without having to replace batteries,” she says.
“The key performance parameter of this chip is that we were able to achieve a peak efficiency of more than 80%, even with such limited power, without compromising the necessary tasks required by the chip,” the expert says, also pointing out that a single inductor is used and shared between many power management circuits to reduce the system size.
According to the team, the chip resolves the issue of limited efficiency when the input power to the energy harvesting IC is below one mircowatt. “There are many applications where the amount of power is less than one microwatt,” says El-Damak, mentioning infrastructure monitoring in low light conditions and wearable biomedical applications, such as systems powered though biological energy sources.
The research advance could impact future solar cell designs and help bring forth advanced energy storage solutions. The design is well-suited for devices with limited input power, such as tiny solar cells or flexible cells, according to the researchers.
El-Damak concludes that these ultralow-power techniques can have a positive impact on various other energy harvesting sources that produce less than one mircowatt. Looking ahead, she and her team want to expand these ideas to cover other sources as well, she says.
Written by Sandra Henderson, Research Editor, Solar Novus Today