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Application Notes |
Low power conversion for energy harvesting
There is plenty of ambient energy in the world around us and the conventional approach for energy harvesting has been through solar panels and wind generators.
However, new harvesting tools allow us to produce electrical energy from a wide variety of ambient sources. Furthermore, it is not the energy conversion efficiency of the circuits that is important, but more the amount of “average harvested” energy that is available to power it. For instance, thermoelectric generators convert heat to electricity, Piezo elements convert mechanical vibration, photovoltaics convert sunlight (or any photon source) and galvanism converts energy from moisture. This makes it possible to power remote sensors, or to charge a storage device such as a capacitor or thin film battery, so that a microprocessor or transmitter can be powered from a remote location without a local power source.
Nevertheless, it is at the “low” end of the power spectrum, where nanopower conversion in WSNs and sensors is becoming more common, that the need for power conversion ICs which can work with very low levels of power and current are needed. These are often 10s of microwatts and nanoamps of current, respectively. However, the availability of such power conversion products, including battery chargers, operating at sub-1µA of current are extremely limited.
In general terms, the necessary IC performance characteristics needed for inclusion in these applications include the following:
- Low standby quiescent currents – typically less than 6µA and as low as 450nA
- Low start-up voltages – as low as 20mV
- High input voltage capability – up to 34V continuous and 40V transients
- Ability to handle AC inputs
- Multiple output capability and autonomous system power management
- Maximum Power Point Control (MPPC) for solar inputs
- Compact solution footprints with minimal external components