National Semiconductor Introduces Industry's First TRIAC Dimmable LED Driver With Both Full-range and Flicker-free Dimming

Constant-current Controller Extends LED Lifetime with Patent-pending Control Architecture

WASHINGTON, Feb. 17 /PRNewswire-FirstCall/ -- APPLIED POWER ELECTRONICS CONFERENCE -- National Semiconductor Corp. (NYSE: NSM) today introduced a new constant-current controller that enables off-line, uniform, flicker-free dimming of high-brightness light-emitting diodes (LEDs) with a conventional TRIode for Alternating Current (TRIAC) forward or reverse phase-control wall dimmer. The LM3445 TRIAC dimmable LED driver enables a full 100:1 range of dimming capability and can maintain greater than 1A of constant current to large strings of LEDs in a variety of residential, architectural, commercial and industrial applications.


The LM3445 TRIAC dimmable LED driver maximizes the light output for systems while maintaining ENERGY STAR(R) power factor requirements in a typical application, positioning it among National's PowerWise(R) family of energy-efficient products. The new driver will be demonstrated in National's booth #426 at the Applied Power Electronics Conference (APEC) 2009 conference in Washington, D. C., from Feb. 15 to 18.

Today's TRIAC wall dimmers are designed to interface with a resistive load such as incandescent or halogen light bulbs. Since an LED bulb does not appear as a resistive load to the TRIAC wall dimmer, dimming an LED bulb using a conventional TRIAC wall dimmer does not yield optimal dimming performance. LED drivers available today cause either a 120 Hz flicker of the LEDs or do not enable the full 100:1 dimming range. National's LM3445 overcomes this challenge by translating the TRIAC-chopped waveform to a DIM signal and decoding it for a full-range of uniform, flicker-free dimming. The driver's patent-pending control architecture maintains constant ripple through the LEDs, which extends the life of the LEDs. To view a demonstration online of the LM3445 and learn more about LED lighting, visit

National's LM3445 LED driver enables direct LED bulb replacement of existing incandescent or halogen bulb systems connected to standard TRIAC wall dimmers. In addition, the LM3445 allows master-slave operation, enabling control of multiple strings of LED bulbs.

A complete LED system featuring the LM3445 can be created in minutes with National's WEBENCH(R) LED Designer. To start a design, visit

Technical Features of National's New LM3445 TRIAC Dimmable LED Driver

Offered in a 10-pin mini SOIC package, National's LM3445 is an adaptive constant off-time AC-DC buck (step-down) constant current controller that includes a TRIAC dimming decoder. The decoder allows wide-range LED dimming using standard TRIAC dimmers. The high-frequency capable architecture allows the use of small external passive components.

The LM3445 includes a bleeder circuit to ensure proper TRIAC operation by allowing current flow while the line voltage is low to enable proper firing of the TRIAC. A passive power factor correction circuit ensures good power factor by drawing current directly from the line for most of the cycle, and provides a constant positive voltage to the buck regulator. Additional features include thermal shutdown, current limit and under-voltage lockout.

For more information on the LM3445 or to order samples and an evaluation board, visit

About National's WEBENCH LED Designer

With National's WEBENCH LED Designer suite of tools, engineers can configure a system with up to 60 LEDs in serial or parallel strings. With a single keystroke, the tool selects from hundreds of high brightness LEDs, matches an LED with one of National's PowerWise energy-efficient LED drivers and creates an optimized power supply circuit. The engineer can easily "dial-in" their size and efficiency requirements, and then simulate the circuit behavior under dynamic conditions, including start-up, steady state, pulse-width modulation dimming and line transient. After fine-tuning the system in just minutes, the 'BuildIt!' feature provides a complete bill of materials for the LED circuit and the ability to quickly ship a custom prototype kit containing the selected LED, PC board, driver IC and passive components.

    Availability and Pricing
    The LM3445 is available now and priced at $1.75 in 1,000-unit quantities.

About National Semiconductor

National Semiconductor creates energy-efficient analog and mixed-signal semiconductors. Its PowerWise products enable systems that consume less power, extend battery life and generate less heat. Headquartered in Santa Clara, Calif., National reported sales of $1.89 billion for fiscal 2008 which ended May 25, 2008. Additional company and product information is available at

National Semiconductor, WEBENCH and PowerWise are registered trademarks of National Semiconductor Corporation. ENERGY STAR is a trademark of the U.S. Environmental Protection Agency and the U.S. Department of Energy.

     Media Contact                       Reader Information
     Gayle Bullock                       Design Support Group
     National Semiconductor              National Semiconductor
     (408) 721-2033                      (800) 272-9959     

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