Advanced Electronic Driver for Power LEDs with Integrated Colour Management

Compared to conventional lighting devices, light emitting diodes (LEDs) have the well-known advantages of ruggedness and extended lifetime. Furthermore, a combination of red, green and blue (RGB) LEDs can generate light with an adjustable colour. An inconvenient property of LED lighting is the dependence of light output on temperature and lifetime thus resulting in varying chromaticity and luminance. Colour-filtered sensors and an appropriate feedback loop to regulate the LED current will solve this problem, but aging of the colour filters might still introduce unwanted colour shifts. This paper presents a novel driving scheme for RGB LEDs that eliminates the need for colour-filtered sensors and reduces the number of light sensor channels by a factor of three. In order to prove the feasibility of the concept, a buck-derived switchmode current source with integrated colour management has been built up and tested. It can deliver up to 4 times 30 W and will keep the colour coordinates stable within an Deltau'v' of 0.004. Large backlighting units can easily be built by using several of these drivers