LED drivers Phosphor technology - Beriled

What’s your favourite
colour?
> Simon Bramble – austriamicrosystems Applications
RGB LED lighting system design made easy
There is little doubt that lighting, quite literally, changes the way we
look at things. Not so long ago White Light Emitting Diodes (LEDs)
were seen as being the cutting edge of lighting technology with these
devices being fitted into everything from mobile phones and children’s
toys to architectural lighting. Now the world of illumination is changing
and Red Green Blue (RGB) LED lighting is stealing more attention.
RGB LEDs allow the user to modulate the colour spectrum. This can be
used to paint a more appealing picture of the subject being lit as well as
to produce stunning ‘mood’ lighting for rooms, displays or even whole
buildings. Fluorescent lights, although cheap to run, give out a colour
high in blue wavelength so can look cold. RGB LEDs allow the user to
change the lighting colour dynamically, depending on what is being lit,
as frequently as desired. Simply choose your favourite colour!
FIG 1 – AS3691 block diagram
Copyright © 2007 Luger Research & LED professional. All rights reserved.
RGB LED driving
The mobile phone industry has caused many manufacturers to design
solutions for driving white LEDs, but there are very few suppliers
providing an adequate solution for driving RGB LEDs.
Many solutions for driving RGB LEDs have well known shortcomings:
Current control is inaccurate. Current variations greater than 2%
cause a noticeable change in colour, therefore the current accuracy
of the driver must be at least +/- 1%. Most LED drivers and discrete
solutions can’t reach this required accuracy.
Many external components required and therefore a less attractive
Bill of Material
Problems with thermal management
Difficulties in building large systems with high colour uniformity
EMC issues due to limited speed of DCDC converter loops
The solution shown below resolves all of these issues and is suitable for
both portable and non portable applications. It can be used for tiny RGB
solutions up to large scale lighting systems controlling several thousands
LEDs. The chip itself occupies only 16mm2 of board space.
www.led-professional.com LED professional Review | June 2007 | page 2
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