Project Lighting - April 2008 - (Page 7)

CoveR stoRy controllers most commonly used to power HBLEDs, the MAX16820 LED driver employs hysteretic control. There is no controlloop compensation, which simplifies the design and further minimizes component count. An integrated high-voltage current-sense amplifier and up-to-2-MHz switching frequency reduce space and component-count, making it ideal for light sources such as the energy-efficient LED based MR16 as well as front and rear automotive lighting (RCL, DRL, and fog/low-beam lights) applications. switch-moDE buck boost or boost DrivEr FIg 2 uSing a SWitch-moDe SteP-DoWn, Buck conVerter DriVer minimizeS the PoWer DiSSiPation anD maXimizeS the DriVer efficiency in a light fiXture. In a buck boost configuration, a floating current-sense amplifier is required to measure and regulate the LED current. Additional protection circuits are also required such as overvoltage protection in case the LEDs fail open or when the LEDs are shorted. The buck boost circuit is ideal for driving high-power LEDs in automotive front-light applications where the input voltage can change from 5.5 V for cold crank to 24 V for double-battery conditions. The driver also needs to withstand over 40-V load dump spikes. LED Dimming 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 dim down in an abnormal highbattery-voltage condition. switch-moDE stEp-Down, buck DrivEr When the input voltage is higher than the total voltage across 7 | Project lighting | aPr 08 the LED string, it is best to use a switch-mode step-down, buck converter driver (see Figure 2), which minimizes the power dissipation and maximizes the driver efficiency in a light fixture. Unlike general-purpose buck When the input supply voltage varies above or below the total voltage across the LED string, a bBuck boost driver topology is used. If the input voltage is always lower than the total voltage across the LED string, then a boost converter is necessary. Reducing the LED current will reduce the LED brightness, but its emission spectrum will shift. This approach is not recommended for some applications. To maintain the emission spectrum over different brightness levels, it is best to keep the dc current 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

Table of Contents Feed for the Digital Edition of Project Lighting - April 2008

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

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.