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Exploring opportunities in green power

Posted: 17 Aug 2012     Print Version  Bookmark and Share

Keywords:Piezo  mechanical vibration  thermoelectric generators 

Furthermore, a principal benefit of digital power system management is reduced design cost and faster time to market. Complex multi-rail systems can be efficiently developed using a comprehensive development environment with intuitive graphical user interface (GUI). Such systems also simplify in-circuit testing (ICT) and board debug by enabling changes via the GUI instead of soldering in "white wire" fixes. Another benefit is the potential to predict power system failures and enable preventive measures, thanks to the availability of real-time telemetry data. Perhaps most significantly, DC/DC converters with digital management functionality allow designers to develop "green" power systems that meet target performance (compute speed, data rate, etc.) with minimum energy usage at the point of load, board, rack and even installation levels, reducing infrastructure costs and the total cost of ownership over the life of the product.

Linear Technology's LTC3880 is a dual output synchronous step-down DC/DC current mode controller with integrated power FET gate drivers and power management features accessed via the I2C-based PMBus. The product's precision reference and temperature-compensated analogue current-mode control loop offer ±0.5 per cent DC accuracy, easy compensation that is calibrated to be independent of operating conditions, cycle-by-cycle current limit, and fast and accurate current sharing and response to line and load transients without any of the ADC quantisation-related errors found in products utilising "digital" control. The LTC3880 incorporates a 16bit data acquisition system that provides digital read back of input and output voltages and currents, duty cycle and temperature. The part also includes a fault logging capability via an interrupt flag along with a "black box" recorder that stores the state of the converter operating conditions just prior to a fault. Multi-rail system development is facilitated though LTC's LTpowerPlay development software and GUI interface.

How much power is there?
State-of-the-art and off-the-shelf energy harvesting technologies, for example in vibration energy harvesting and indoor photovoltaic cells, yield power levels in the order of milliwatts under typical operating conditions. While such power levels may appear restrictive, the operation of harvesting elements over a number of years can mean that the technologies are broadly comparable to long-life primary batteries, both in terms of energy provision and the cost per energy unit provided. Furthermore, systems incorporating energy harvesting will typically be capable of recharging after depletion, something that systems powered by primary batteries cannot do.

Ambient energy sources include light, heat differentials, vibrating beams, transmitted RF signals, or just about any other source that can produce an electrical charge through a transducer. The table illustrates the amount of energy that can be produced from different energy sources.

Table: Energy sources and the amount of energy they can produce.

There are a plethora of applications where these power levels make sense for a system deployment. Here are just a few examples:

 • Aircraft corrosion sensors
 • Auto dimming windows
 • Bridge monitors
 • Building automation
 • Electricity usage meters
 • Gas sensors
 • Health monitors
 • HVAC controls
 • Light switches
 • Remote pipeline monitors
 • Watches
 • Water meters

Conclusion
Opportunities for energy harvesting for use in green power alternative energies are abundant and plentiful. An excellent example of these opportunities is presented by the market for solar-powered electronic devices. It continues to grow as companies look for ways to reduce energy consumption. Consider smart meters for instance. These are deployed on the smart grid and would like to be powered by an ambient energy source in order to reduce operating energy costs. And one viable and abundant source of energy comes from solar power. However, because solar power is variable and unreliable, nearly all solar-powered devices feature rechargeable batteries. Thus, an important goal would be to extract as much solar power as possible to charge these batteries quickly and to maintain their state of charge for use as an energy source when solar power is not available.

Conversely, if smart meters used batteries as their primary power sources, then the power conversion and management electronics would need to have very low quiescent currents in a standby mode in order to extend battery life.

About the author
Tony Armstrong is director of product marketing, Power Products, Linear Technology Corp.

To download the PDF version of this article, click here.


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