Harry Rodriguez

A Probabilistic Approach of Designing Driving Circuits for Strings of High-Brightness Light Emitting Diodes

Often, high brightness LEDs (HB-LED) are connected in series to create strings. According to their data sheets, the HB-LEDs have a variation in their forward voltage drop. This forward voltage variation may create a non-uniform illumination if the strings are connected in parallel. This paper proposes a probabilistic approach for modeling the forward voltage drop across the HB-LEDs and determining the value of the resistance needed in each string to control the current. The results of this paper show that when the probabilistic models are used, the value of the added balancing resistance is reduced compared to when using standard worst case models.

Effects of parametric uncertainty in designing a high-brightness LED light system

One way to create white light is with a RGB color mixing system, in which light from multiple monochromatic LEDs (red, green and blue) is mixed. Unfortunately, there are several variations/uncertainties between individual LEDs that can create unwanted problems, such as variations in: forward voltage drop, peak wavelength, spectral radiant intensity, and the width of the spectral power distributions (SPD) of the LEDs. This paper will explain, through experiments, behavioral models and probability theory, how the variations affect the design of LED based lighting system. We especially describe the effects such as the influence of SPD variation and Forward Voltage drop variation.