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, making the dimmer 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.
The new chip solves this issue by dynamically adjusting the current through the phase dimmer. Dynamic hold circuitry, coupled with a programmable, intelligent dimming decoder, ensures smooth, consistent illumination across the full dimming range. The LM3450 LED driver also provides active power factor correction, ensuring a high power factor that complies with residential and commercial Energy Star standards.
The integrated phase dimming decoder interprets the phase angle and remaps it to a 500-Hz PWM output to dim the LEDs. The phase-dimming decoder uses programmable mapping from input to output for better 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 adjustments.
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 better noise immunity.
For more information or to order samples and an evaluation board: http://www.national.com/pf/LM/LM3450.html
