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Optoelectronics/Displays??

Integrate SMPS control in LED applications

Posted: 01 Jul 2008 ?? ?Print Version ?Bookmark and Share

Keywords:LED driver? solid state lighting? hysteretic buck converter?

Solid-state lighting is quickly becoming one of the most exciting fields in electromechanical engineering and design. The LED offers a combination of flexibility and efficiency that is unmatched by conventional forms of lighting. LEDs are being adopted in architectural and stage lighting applications because of their ability to emit highly reliable, long-lasting light from small packages. Each particular lighting application is unique, however, because every marketing department finds value in different features. Consequently, there are more and more specialized ICs on the market that are added to already dizzying catalogs and distribution models. Programmable mixed-signal MCUs are being adopted rapidly because a single device can integrate a wide range of peripherals. Such peripherals include pulse-width modulators (PWM), communication interfaces, amplifiers, comparators and data converters.

Complex functions, such as dimmable buck converters, are controllable by combining some of the peripherals described above. Buck converters used in LED driver applications are required to be current mode regulators because LEDs are current mode devices. The LED V-I curve shows that slight variations in the forward voltage will have exponential effects on the current. Hence, the feedback in any LED driver circuit should represent the current. Additionally, constant current is used because the color and intensity of LEDs are rated and binned at particular forward current levels by manufacturers. These properties are important because they are used as values to maintain compliance with overall system specifications.

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