Project Lighting - April 2008 - (Page 13)

FeAtURe an analytical approach to cooling hBleDs as high-brightness leDs replace traditional light sources, careful approaches are needed for effective thermal management By norman Quesnel | advanced thermal Solutions | norwood, ma | www.qats.com Contents Viewpoint Selecting HBLED Drivers for Lighting Apps Simulation Technique for Optimizing White-LED Design An Analytical Approach to Cooling HBLEDs hough cool to the touch, high-brightness LEDs (HBLEDs), with their higher power needs, require direct cooling methods to keep within normal operating temperatures. Without them, the light output of a HBLED will be much shorter than normal. insiDE-out managEmEnt T heat management should be considered from the inside out, starting with its semiconductor die junction. The junction must be kept at or below the maximum rated temperature. Here, thermal control is achieved mainly by conduction. It starts at the junction and ends with natural convection and/or radiation of heat to the ambient. Unfortunately, the heat transfer from source to ambient is not free flowing. Thermal resistances at different points pose major obstacles. As with other ICs, the highest thermal resistance in the heat transfer path is the junction-to-case thermal resistance (R j-c) of the package. Spreading resistance is also an impediment to thermal transfer. As the power dissipating from HBLEDs increases, and clusters of multiple diodes produce considerable aggregate heat, different kinds of circuit boards are needed. Thermally enhanced spreader materials, such as multilayer FR4 PCBs, ceramic and metal-core boards, cold plates, and vapor chambers are viable systems to Lighting News Home Page Product Training Module Online Ordering Suppliers Catalog HBLED thermal management systems now in use are closer to those used for cooling hot computer chips than incandescent light bulbs. Unlike a light bulb, where most heat will radiate into the air, LED 13 | Project lighting | aPr 08 http://www.qats.com http://digikey.com/ http://ad.doubleclick.net/clk;198717884;26055153;t http://ad.doubleclick.net/clk;198717989;26055167;e 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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