A novel led driving circuits development for decorative lighting system energy saving

Abstract

The forward current draft with the temperature changes is a characteristic of LED. This research used this characteristic to achieve control optimization of LED by the forward current feedback. Temperature detection through forward current measurements was applied to LED PWM to carry out the best thermal management of LED arrays under temperature variations, which can offer steady illumination and keep constant chromaticity. LED spotlight products are mainly used for lighting show box display to replace the incandescent lamp which has been forbidden by EU from the year of 2009. Such kind of products now is available on the market. However, the illumination decay and chromaticity changes with operation temperature obstruct wide distribution of LED spotlight for decorative lighting systems. The developed technology by this research can be used to control the chromaticity and the illumination of the LED spotlight and a great niche is outward. This research tested various types of LED are provided by different manufacturers, and the database of the changes of LED chip grains against forward current is build. Constant temperature bath was employed to get the curve of forward current and temperature, which will be a basis of forward current feedback and temperature conversions. Self-developed driving circuits were used to control LED to make the relative illumination decays to be less than 5% and the coordinate excursion of Color rendering index on the CIE chromaticity diagram is lower than 0.1. The circuit control of LED spotlight with low difference of illumination and Color rendering index were therefore successfully realized in this study.