Products, Materials + Tools | Dec 01, 2010

National Semiconductor Introduces LED Driver with Extraordinary Phase-Based Dimming Capabilities

National Semiconductor Corp. introduced a new LED driver with the industry’s best phase-based dimming performance for high-brightness light-emitting diode (LED) applications. The LM3450 LED driver integrates active power factor correction (PFC) and phase dimming decoding to provide uniform, flicker-free illumination across a wide, programmable dimming range. A member of National’s PowerWise energy-efficient product family, the LM3450 is well-suited for use in high-performance, phase dimmable, 10 Watt to 100 Watt LED fixtures.

Residential and commercial Lighting applications that interface with phase-based dimmers require circuitry that can correctly decode a phase-chopped waveform to provide proper dimming of the LEDs. Dimmable LED drivers available today do not always meet the minimum current requirement for forward phase or TRIAC-based dimmers, causing the dimmer to shut off or “misfire” during operation. This causes inaccurate decoding of the phase angle resulting in flicker, particularly at very low dimming levels. To compensate, today’s drivers reduce the LED dimming range or continuously burn power to keep the dimmer from misfiring.

National Semiconductor has taken a unique approach to solving this issue with its new LM3450 LED driver that integrates hold circuitry to dynamically adjust the current through the phase dimmer. The dynamic hold circuitry, coupled with a programmable, intelligent dimming decoder, ensures smooth, consistent illumination across the full dimming range. This combination of features provides the most efficient and uniform dimming performance in the industry. The LM3450 LED driver also provides active power factor correction, ensuring a high power factor that complies with residential and commercial Energy Star standards.

Technical Features:
■ Critical conduction mode PFC
■ Over-voltage protection
■ Feedback short circuit protection
■ 70:1 PWM decoded from phase dimmer
■ Analog dimming
■ Programmable dimming range
■ Digital angle and dimmer detection
■ Dynamic holding current
■ Smooth dimming transitions
■ Low power operation
■ Start-up pre-regulator bias
■ Precision voltage reference

Applications:
■ Dimmable downlights, troffers, and lowbays
■ Indoor and outdoor area SSL
■ Power supply PFC

The LM3450 LED driver regulates an accurate output while maintaining excellent power factor at the input. The integrated phase dimming decoder interprets the phase angle and remaps it to a 500 Hz PWM output to dim the LEDs. This combination of features is ideal for implementing a phase dimmable off-line LED driver for 10 Watt to 100 Watt loads.

The phase dimming decoder uses programmable mapping from input to output to increase design flexibility. It also features a dynamic filter and variable sampling rate for a fast, smooth response to dimmer movement. An integrated dynamic hold circuit ensures that the phase dimmer angle is decoded properly while minimizing the extra power losses associated with holding current.

Other benefits include an analog adjust input to allow for differentiation such as thermal foldback, interface to sensors or dimmer range adjustability. The LM3450 can be implemented in either single stage or two stage configurations. The single stage configuration yields the smallest footprint and allows for the highest efficiency when converting from the AC mains voltage. The two stage configuration provides improved dimming performance and better noise immunity.

For additional information please visit http://www.national.com or download the datasheet and application notes.

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