LED Driver Integrates Power Factor Correction and Phase Dimming Decoding

NationalSemiconductor Corp.'s LED driver with phase-based dimming performance is forhigh-brightness light-emitting diode (LED) applications. The LM3450 LED driverintegrates active power factor correction (PFC) and phase dimming decoding toprovide uniform, flicker-free illumination across a wide, programmable dimmingrange. A member of National's PowerWise energy-efficient product family,the LM3450 is well-suited for use in high-performance, phase dimmable, 10 to100W LED fixtures.

NationalSemiconductor's LM3450LED driver integrates hold circuitry to dynamically adjust the current throughthe phase dimmer. The dynamic hold circuitry, coupled with a programmable,intelligent dimming decoder has a smooth, consistent illumination across thefull dimming range. This combination of features provides an efficient anduniform dimming performance. The LM3450 LED driver also provides active powerfactor correction, for a high power factor that complies with residential andcommercial Energy Star standards.

The LM3450 LED driverregulates an accurate output and the integrated phase dimming decoderinterprets the phase angle and remaps it to a 500 Hz PWM output to dim the LEDs.This combination of features is useful for implementing a phase dimmableoff-line LED driver for 10 to 100W loads.

The phasedimming decoder uses programmable mapping from input to output to increasedesign flexibility. It also features a dynamic filter and variable samplingrate for a fast, smooth response to dimmer movement. An integrated dynamic holdcircuit ensures that the phase dimmer angle is decoded properly whileminimizing the extra power losses associated with holding current.

Otherbenefits include an analog adjust input to allow for differentiation such asthermal foldback, interface to sensors or dimmer range adjustability.

The LM3450 can beimplemented in either single stage or two stage configurations. The singlestage configuration yields the smallest footprint and allows for the highestefficiency when converting from the ac mains voltage. The two stageconfiguration provides improved dimming performance and better noise immunity.

National'sLM3450 is offered in a 16-pin TSSOP package and is priced at $1.85 in1,000-unit quantities.