At 07:36 AM 6/25/2004 -0700, you wrote:
>Interesting idea! Seems like I could just use a rail to rail op amp with
>the LED between output and inverting input. Current sense resistor between
>inverting input and ground. Reference voltage on non-inverting input.
>
>Thanks!

Yes, most likely with poorer to much poorer dropout performance. Watch the
supply voltage of the op-amp too, many R-R types these days can't handle
your 10V. The rather mature (ca. 1976) LM10 will operate from as low as 1.2V
(which is lower than the Vf of any visible LED) up to 40V-45V. Really one of
Robert Widlar's finest pieces of work.

Here's a 22M TIF of him looking at the LM10 layout (DON'T download unless you
have a good connection or lots of time-- 22M):

http://appsrv.national.com/gallery1/231/231_rgb.tif

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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