National Semiconductor intoduces TRIAC Dimmable LED Driver

18th February 2009

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Datasheet

National Semiconductor has introduced a 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 power factor requirements in a typical application, positioning it among National’s PowerWise 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.

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 LED Designer.

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.