Sliding Mode Pulsed Current Averaging IC Drivers for High-Brightness Light Emitting Diodes

SynDiTec Inc.,
San Jose, CA

This project developed new light emitting diode (LED) driver ICs associated with specific (uniquely operated) switching power supplies that optimize performance for High Brightness LEDs (HBLEDs). The drivers utilize a digital control core with a newly developed nonlinear, hysteretic/sliding mode controller with mixed-signal processing. The drivers are flexible enough to allow both traditional microprocessor interface as well as other options such as “on the fly” adjustment of color and brightness.

The SynDiTec pulsed current averaged hysteretic controller stabilizes the LED current to 20mA, while maintaining safe inductor current values.

Some other unique features of the newly developed drivers include:

AC Power Factor Correction
High power efficiency
Substantially fewer external components should be required, leading to substantial reduction of Bill of Materials (BOM).

Thus, the LED drivers developed in this research optimize LED performance by increasing power efficiency and power factor. Perhaps more remarkably, the LED drivers provide this improved performance at substantially reduced costs compared to the present LED power electronic driver circuits. Since one of the barriers to market penetration for HB-LEDs (in particular “white” light LEDs) is cost/lumen, this research makes important contributions in helping the advancement of solid-state lighting (SSL) consumer acceptance and usage.

The U.S. Department of Energy projects that a potential reduction of electricity used for illumination could be up to 50% by 2025 if SSL becomes widespread. Benefits of this would be >1015 Wh of electrical power savings, which would lead to a reduction of almost 1 billion tons of carbon dioxide emission (among many other significant emission reductions). Presently, however, the cost/lumen for SSL is prohibitively high for market penetration into the general white light illumination market. This project aids in reducing the cost of SSL High Brightness white lighting systems. LED driving, pulsed average sliding mode digital controllers were developed. The drivers require no additional expensive circuits that are currently being used for systems with similar features.

Analytical and mathematical simulations showed that for two operational input voltages, DC and AC, Pulse Current Averaging Hysteretic Control works to drive HB LEDs. SynDiTec Inc. considers this to be a theoretical contribution to Automatic Control Theory by investigating and developing a new digital pulse current averaging controller. That allows dropping traditional PWM or PFM feedback techniques and coming up with new techniques suitable to digital implementation IC architecture. As the result, this controller is simple, low-cost, and feasible for driving HB LEDs as well as traditional switching power supplies loads. Some other advantages of this method appear to be:

Inherent pulse-by-pulse current limiting, making the power converter nearly immune to damage from overload.
No external compensation needed (low parts count).
Fast response of the inductor current.
Automatic power factor correction in off-line drivers
Robustness and increased noise immunity
Programmable output current for brightness regulation and different compensation of drifting LED parameters.

This work was done by Dr. Anatoly Shteynberg of SynDiTec Inc.