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Optoelectronics/Displays??

Controller drives flicker-free LED dimming

Posted: 16 May 2012 ?? ?Print Version ?Bookmark and Share

Keywords:LED controller? LM3447? LED driver?

Texas Instruments Inc. has unveiled the LM3447 AC/DC LED controller, introducing it as the first such device with constant power regulation. The driver features a dimmer detect, a phase decoder, and adjustable hold current circuits to provide smooth and flicker-free dimming operation in off-line, isolated LED lighting applications, including A19, E26/27 and PAR30/38 bulbs, as well as can light retrofits.

Traditional drivers use constant current control to accurately regulate LED forward current. This approach produces consistent light output or intensity from LEDs in the same bin. However, once current is applied to the LED, its solder point temperature rises, leading to a decrease in forward voltage and a drop in efficacy. Conversely, by using the new LM3447 with constant power regulation, the LED forward voltage droop over temperature is offset by an increase in LED current to maintain constant LED power. The result is up to 10-percent improvement in efficacy across the expected operating temperature range of the fixture.

The LM3447 LED driver offers integrated phase dimmer decoding and dimmer detection circuitry allows for easy design and highest efficiency. It operates with leading edge (TRIAC) and trailing edge dimmers. Primary side control supports isolated lighting designs without opto-couplers, and constant power LED load regulation improves efficacy of LED array by compensating for LED junction temperature changes.

Its fixed frequency discontinuous conduction mode flyback topology with valley switching simplifies EMI filter design, while greater than 0.9 power factor correction meets all regulatory requirements.

Its thermal fold-back protects LED arrays from overtemperature while providing reduced light output, and LED open- and short-circuit protection and driver IC thermal shutdown protect lamp electronics from damage during fault conditions.

The LM3447 comes in a 14-pin TSSOP package at the suggested retail price of $1.15 in 1,000-unit quantities. It is available in volume now.





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