Project Lighting - April 2008 - (Page 11)

CoveR stoRy sponsoR ADveRtIsement Catalyst Semiconductor’s CAT4139 White LED Driver The CAT4139 is a DC/DC stepup converter that delivers a constant current ideal for driving LEDs. An operating frequency of 1MHz allows the device to be used with small value passive components. LEDs connected in series are driven with a regulated current set by an external resistor. The CAT4139 is ideal for driving parallel strings of up to five white LEDs in series or up to 22V. LED dimming can be done using a DC voltage, a logic signal, or a pulse width modulation (PWM) signal. The device is housed in a low profile 5-lead TSOT-23 package for space critical applications. click here for more information allows spontaneous emission spectra to be embedded in the simulations and then evolved as the rays traverse regions of stimulated gain, absorption, and luminescence. There are four possible spectral-evolution processes: Part of the spontaneous spectrum is amplified by stimulated emission in the QWs—this is a carrier recombination process.Part of the spontaneous spectrum is absorbed to generate electronhole pairs to be subjected to electrical transport—this is a carrier generation process. Part of the absorbed spectrum is instantaneously re-emitted, thereby modifying the emission isotropy of that active cell. Part of the spectrum is spectrally converted in the luminescent region. These spectral-evolution processes consequently give rise to a modified spontaneousemission spectrum. The first Catalyst Semiconductor 2975 Stender Way Santa Clara, CA 95054 USA: +(1) 800-258-5991 Outside USA: +(1) 408-542-1000 http://www.catsemi.com/ three processes constitute a novel photon-recycling model that includes amplified spontaneous emission. Since brighter LEDs require highercurrent injection, the active region (QWs) is pumped with enough carriers for stimulated emission to occur. Stimulated emission will amplify the spontaneous emission spectrum, giving rise to amplified spontaneous emission (ASE). Although ASE has been studied extensively in resonating structures such as lasers, optical amplifiers, resonant-cavity LED (RCLED) and super-luminescent LED (SLED), the inclusion of ASE in the non-resonant structures typical in modern white-LED design has not been fully explored, and is now enabled by this novel photon-recycling model. The photons production/ absorption and carrier recombination/generation are carefully balanced to Contents Viewpoint Selecting HBLED Drivers for Lighting Apps Simulation Technique for Optimizing White-LED Design An Analytical Approach to Cooling HBLEDs Lighting News Home Page Product Training Module Online Ordering Suppliers Catalog 11 | Project lighting | aPr 08 http://digikey.com/ http://www.catsemi.com/ http://ad.doubleclick.net/clk;198717884;26055153;t http://ad.doubleclick.net/clk;198717989;26055167;e http://ad.doubleclick.net/clk;195096811;25485865;w http://ad.doubleclick.net/clk;198717988;26055168;e http://ad.doubleclick.net/clk;198717986;26055170;v http://ad.doubleclick.net/clk;198717985;26055171;v

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Project Lighting - April 2008 Contents Viewpoint About Project Lighting Sponsor Simulation Technique for Optimizing White-LED Design An Analytical Approach to Cooling HBLEDs LED Lighting Needs Smarts to be Competitive Lighting News Enter to Win an iPhone Refernce Materials Lighting Quick Links

Project Lighting - April 2008

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