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SSL LED driver boosts dimming performance

Posted: 09 Feb 2015     Print Version  Bookmark and Share

Keywords:SSL  LED  TRIAC dimmers  OTP 

Dialog Semiconductor has released the iW3688, its first solid state lighting (SSL) LED driver geared towards smooth, flicker and shimmer-free dimming. The iW3688 has an ultra-low bill of materials (BOM) cost for next-generation LED bulbs.

The iW3688 single-stage LED driver is designed for applications up to 20W, including A-style, BR, candle, GU10 and PAR bulbs and T8 LED tubes, as well as external lighting ballast drivers. It uses Dialog's patented digital dimming control technology to provide compatibility with the most challenging TRIAC and digital dimmers, while Dialog's patented digital algorithms enable integrated active biasing for high performance dimming at a lower cost compared to conventional external bleeder circuits.

TRIAC dimmers require a minimum load current to maintain forward conduction. This is a problem for highly efficient, low-power LED bulbs since they may fail to draw enough current through the TRIAC to clear the holding current threshold, resulting in flicker and shimmer in dimmable LED bulbs. Many low-power bulb designs address this issue by using an external bleeder circuit to draw extra current through the TRIAC while it is conducting. However, the disadvantage is these bleeder circuits require additional external components and dissipate additional power inside the bulb, significantly raising the internal temperature and shortening the LED bulb operating lifetime.

The iW3688 eliminates the cost of up to 20 external components in the bulb design, including as many as 10 required for the external bleeder circuit, and instead uses Dialog's integrated digital algorithms that modulate primary FET switching to draw extra current during dimming. This ensures the input current continuously stays above TRIAC biasing thresholds during forward conduction, eliminating the need for an external bleeder circuit. The iW3688 further reduces BOM costs by simplifying the EMI filter circuit and integrating the current sink, switching and VCC charging circuits. Additional savings come from the iW3688's advanced IC power management and voltage sensing, which allow the use of low-cost, off-the-shelf inductors.

The iW3688 integrates Dialog's patented over-temperature protection (OTP) de-rating technology to address LED bulb lifetime issues caused by excessive heat. OTP technology monitors the temperature inside the sealed SSL bulb and seamlessly dims light output if the temperature rises above a safe operating threshold, then restores brightness as temperature falls. This results in cooler operation, avoids exceeding the temperature rating of the electrolytic capacitors, and helps ensure a predictable and safer bulb operating life.

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