New-Tech Magazine Europe | Dec 2015 Digital edition

Power Management Tips for Energy Harvesting Systems European Editors

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power manager more opportunities to avoid problems and optimize the performance. This also helps isolate any devices that are consuming too much power. A buck/boost converter is a suitable architecture for harvesting energy from movement or vibration via a piezoelectric transducer. A protective shunt at the input allows the power manager to accommodate a variety of different piezoelectric elements, which can have short-circuit currents around 10µA. An example of a typical power manager for a piezoelectric source is the LTC3588 from Linear Technology. This is designed to interface directly to a piezoelectric or alternative power source, rectify a voltage waveform and store the harvested energy on an external capacitor, as well as bleed off any excess power via an internal shunt regulator. It integrates a low-loss full-wave

lower limit below which the power stage may either shut down or not start, interrupting the operation of the system. This also means the power up sequencing must understand implications of when to power each device along with other devices so that the power drain does not push the power conversion stage below that lower limit. However, it is also necessary to be aware of the potential peak power to avoid overwhelming the additional energy storage element such as a capacitor or battery. Using hardware timers and interrupts rather than software reduces the overall power requirement, and having status indications and alerts implemented across the systems are essential so that power management choices can be made with the right information. Isolating all the loads in the system and making them switchable gives the

esigning a powermanagement system for a source that

harvests energy from the environment can be challenging. These sources, from solar cells to vibrational energy, and even power from thermal differences, are all small amounts of power that vary unpredictably. This creates a significant challenge for a power management system that has to run efficiently and provide a steady output. The voltage and power requirements of the sensors and processors in the node being powered have dropped, so using an energy harvesting source has become more practical; but there are still different ways to manage these power sub- systems. It is obviously necessary to optimize the design for the low average power in the system, but it is also necessary to understand the lower and upper limits of the energy harvesting source. A buck/boost converter will have a

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