Re: Driving many led's (400+)

On Mon, 19 Jan 2009 13:35:12 -0800, "Paul Hovnanian P.E."
<paul@xxxxxxxxxxxxx> wrote:

Jon Slaughter wrote:

I have an application where I need to drive 400+(~150 rgb's) individually.

I was thinking about using the

TLC5947---TI---24CH 12bit PWM LED Constant Current Driver

as this was the first one I looked at where each LED had it's own channel.

Is that actually a requirement?

That way I had complete control. It whould require 20+ of these and each one
costs about 4$. It seems like a nice package and the only problem I have is
setting the same q current for all of the IC's(so they all have the same
brightness at the same level).

If you are going to be controlling things individually (i.e. in a matrix
display), equal brightness isn't as big an issue. With some LEDs on and
some off, and the display changing, nobody will notice some
non-uniformity.

If the point is to produce a uniform brightness across a panel, you are
going to have problems with LED tolerances. Particularly if you can't
get 1000 of the same P/N, from the same manufacturing batch.

Yes, I had to develop instruments for binning displays based on LEDs
for exactly this reason -- in a matrix with human perceived intensity
along one axis and human perceived color along the other. (monochrome
devices, there.) I also developed instruments for calibrating RGB
arrays so that all the pixels could be driven for video with a uniform
"white" if all are driven that way as well as calibrated mixing of
colors consistent with the CIE models of human perception. There is
some fun work in there.

http://www.infinitefactors.org/misc/images/p1000046_640x480.jpg

I just glanced at Mike H's suggestion of Macroblock MBI5031. I'll
have to look at those a little more later on.

Jon
.

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