LED driver provides 'industry's best' dimming performance

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 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, many drivers reduce the LED dimming range or continuously burn power to keep the dimmer from misfiring. National Semiconductor has sought to address this issue with its LM3450 that integrates hold circuitry to dynamically adjust the current through the phase dimmer. The company says its dynamic hold circuitry, coupled with a programmable, intelligent dimming decoder, ensures smooth, consistent illumination across the full dimming range. It claims that this combination of features provides 'the most efficient and uniform dimming performance in the industry'. The device also provides active power factor correction. An integrated phase dimming decoder interprets the phase angle and remaps it to a 500Hz PWM output to dim the LEDs, suitable for implementing a phase dimmable off line LED driver for 10 to 10oW loads. The phase dimming decoder uses programmable mapping from input to output and the device also features a dynamic filter and variable sampling rate. An integrated dynamic hold circuit has been designed to ensure the phase dimmer angle is decoded properly while minimising the extra power losses associated with holding current. It can be implemented in either single stage or two stage configurations, which National says provides 'improved dimming performance and better noise immunity'.