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Energy harvesting design explored

Wednesday 08 August 2012 00:50

Everyone’s talking about energy harvesting – but what exactly is it? The term is often used as a paraphrase for the whole range of low-power applications, yet the “harvesters” themselves are only one part of a larger system, writes Ingo Seehagen, a field application engineer at Avnet Memec.

Energy harvester circuits are used in electronic systems that need to be self-sufficient in energy – in other words, those that are not powered by mains electricity or batteries. They can also be used to extend battery life.

In all these systems, the collection, transformation, storage and use of energy need to be coordinated with one another. They capture and transform energy from different sources, including thermal, kinetic and optical. One of the issues here is that the energy that results from these transformation processes is often not sufficient to power electronic systems in a reliable way. This is where integrated circuits come in.

These manage all power management functions like capture and storage of the charge, protection against undervoltage, and provision of energy for the system – more or less autonomously. Once they have gone to the trouble of capturing energy, the device clearly shouldn’t waste it. This is why it’s a good idea to use elements that have the lowest possible energy consumption. What do these circuits need to do when they’re in use?

Their objective is to transform, store and make available the energy surrounding the system as effectively as possible so that it can be powered without needing any other energy sources.

Autonomously-powered systems are coming into their own with the widespread and growing availability of electronic components that have very low energy requirements, and the energy harvesting trend is another factor contributing to the rapid growth of these technologies. Taking the example of a wireless sensor, the point is not only to save money implementing it but also reduce its operating cost throughout its useful life.

An energy harvesting evaluation platform developed by Avnet Memec in collaboration with Maxim Integrated Products and Energy Micro is intended to enable developers to learn about energy harvesting and start using these energy-independent systems. The first version is based on the existing evaluation platforms for Maxim Integrated Products’ MAX17710 energy harvester and for the EFM32TG840F32 energy-saving microcontroller from Energy Micro’s Tiny Gecko range.

The MAX17710 incorporates all the power management functions needed for energy harvesting applications. These include functions for charging and protecting the THINERGY Micro-Energy Cell (MEC) from Infinite Power Solutions (IPS), which is integrated in the evaluation kit.

The IC can manage poorly regulated sources such as energy-harvesting devices with output levels ranging from 1µW to 100mW. The device also includes a boost regulator circuit for charging the cell from a source as low as 0.75V. The evaluation board is powered by a solar cell and an internal regulator protects the cell from overcharging. Output voltages supplied to the target applications are regulated using an efficient adjustable low-dropout (LDO) linear regulator with selectable voltages of 3.3V, 2.3V, or 1.8V.


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