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The incandescent light bulb's days are numbered. Over the last century Edison's traditional filament-based design has stood the test of time and become the standard for general illumination applications. But new lighting technologies, in particular light-emitting diodes (LEDs), promise to eventually displace glass-encased incandescent bulbs as well as fluorescent lights.
In a world where escalating costs have every user closely examining power budgets, incandescent technology finds itself on the wrong side of the power efficiency curve. Approximately 97 percent of the energy consumed by an incandescent bulb is wasted in heat. Fluorescent bulbs offer a slightly better option, but still waste up to 85 percent of power consumed. Moreover, both technologies last on average only about 5000 hours before needing replacement. Fluorescent technology also uses toxic Mercury and emits a harsh-colored light. Neither technology can compare to white LEDs which offer a lifecycle ten times as long, do not use toxic materials and can support virtually any color light. Most importantly, LEDs support light conversion efficiencies that rival fluorescents.
| Technology |
Efficiency |
Uses Mercury |
Life |
Color |
| Incandescent |
3% |
No |
2,000 hrs |
Warm, Yellowish |
| Fluorescent |
15% |
Yes |
7,500 hrs. |
Cold, Blueish |
| LED |
12%-20% |
No |
50,000 hrs. |
Anything |
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Table 1. Competing Light Technologies
As a result, a move to LED technology for general illumination applications could greatly reduce energy consumption. A recent study by the U.S. Department of Energy estimated that widespread adoption of white LEDs by 2025 could cut electricity consumption by 10 percent worldwide, and slash up to $100 Billion from electric bills. Those energy savings could reduce carbon dioxide emissions from power plants by up to 350 Megatons a year worldwide according to Sandia National Laboratories. Government leaders have begun to take notice. Recently, for example, Australia announced legislation to phase out the use of inefficient incandescent light bulbs as part of a plan to reduce the generation of greenhouse gas emissions and cut household power bills.
While white LEDs offer an attractive alternative to current high-volume lighting technologies, designers attempting to collapse the electronics required to drive LEDs into the base of a light bulb face major challenges. Space constraints demand a small, efficient footprint. At the same time thermal considerations, which can have a major impact on device reliability, place restraints on design density. Finally, designers must also carefully consider the impact of EMI on their design.
Since the drive electronics are not user accessible, designers can use non-isolated, commercial-off-the-shelf (COTS) inductor-based buck and buck-boost switched mode power supply (SMPS) converters in low power (≤3 W) lighting applications. Both of these circuits eliminate the bulk and expense of a transformer and offer a number of other advantages. This article will compare these two topologies and discuss the tradeoffs associated with each one.
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