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EETE SEP 2015

Energy Harvesting An adaptive power management solution for energy harvesting EBy Bruce Haug nergy surrounds us everywhere and is available in the form of temperature, light, galvanic and even electromechanical energy. However, the energy from these sources is often found in such minute quantities that it cannot continuously supply adequate power for any viable purpose. In fact, until recently, it has not been possible to capture sufficient energy to perform any useful function, with the exception of solar and geothermal. Energy Harvesting is the process of capturing minute amounts of energy from one or more of these naturally occurring energy sources, then accumulating or storing them for later use. Energy harvesting devices can efficiently and effectively capture, accumulate, store, condition and manage ambient energy and condition them in a form that can be used to perform useful functions. Recent technical advancements have increased the efficiency of devices in capturing trace amounts of energy from the environment, transforming it into electrical energy. In addition, advancements in converter technology have not only increased power conversion efficiency but have also reduced their internal power consumption requirements. These developments have sparked interest from the engineering community to develop even more applications that utilize energy harvesting. Energy harvesting from an ambient source, where a remote application is deployed, and where a natural energy source is essentially inexhaustible, is an increasingly attractive alternative to wired power or batteries. These essentially free energy sources, when utilized properly, can be maintenance-free and are usually available throughout the working lifetime of many applications. Alternatively, energy harvesting can be used as a secondary energy source to supplement a primary power source such as a battery to greatly extend the life of the battery, reducing maintenance costs. Energy harvesting applications Many real life applications using energy harvesting as the main power source are now in use. Wireless sensor networks (WSNs), for example, often benefit from energy harvesting power sources. When a wireless node is deployed at a remote site where wired power or a battery is either unreliable or unavailable, energy harvesting can supply the power needed to operate it. In other situations, multiple energy sources can be used to enhance the overall efficiency and reliability of a given system. Some of the most common energy harvesting sources include mechanical energy from sources such as vibration, mechanical stress and strain; thermal energy from waste energy by-product from furnaces, heaters, motors and friction sources; light energy captured from sunlight or room lighting via photo diodes, or solar cells; electromagnetic energy from inductors, coils and transformers; natural ambient energy from the environment such as wind, water flow, ocean currents, galvanic and solar; human body through a combination of mechanical and thermal energy generated or through actions such as kinetic movement; and other energy from chemical and biological sources. It is important to note that all these energy sources are virtually unlimited and essentially free, if they can be captured at, or near, the system’s point of deployment. A typical energy harvesting system requires an energy source such as vibration, heat or light plus some key electronic components. These include an energy conversion device (transducer) such as a piezoelectric element or solar panel that can translate the ambient energy source into electrical form; an energy harvesting conversion IC that captures, stores and manages power; sensors, microcontrollers and a transceiver to read, record and transmit the data as part of the WSN; optional supplementary energy storage device such as thin-film or primary cell battery or super capacitor. It is very important that the power conversion device have a high efficiency and a low quiescent current so as to allow most of the harvested energy to be used for powering the sensor network or control and monitoring device. Furthermore, it is essential to understand how much average power is available from the harvestable energy source and how much energy is required to power the device being powered (its duty cycle of operation). Energy harvesting IC solutions Fortunately Linear Technology has several energy harvesting devices for processing, storage and utilization of harvestable energy. The LTC3106 is one such device that is a highly integrated, ultralow voltage buck-boost DC/DC converter with automatic PowerPath management optimized for multiple input sources and low power systems. If the primary power source is unavailable, the LTC3106 seamlessly switches to the backup power source and is compatible with either rechargeable or primary cell batteries and can trickle charge a backup battery whenever there is surplus energy available. If a light source is used, an optional maximum power point control ensures power transfer is optimized between power source and load. At no load, the LTC3106 draws only 1.6μA Bruce Haug is Senior Product Marketing Engineer for Power Products at Linear Technology Corporation – www.linear.com Fig. 1: The LTC3106 uses either a solar panel or primary battery to provide continuous power to a downstream load. 30 Electronic Engineering Times Europe September 2015 www.electronics-eetimes.com


EETE SEP 2015
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