The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: "R. Lewis"
Subject: Re: current source for array of infrared leds
Date: Tue, 3 Dec 2002 21:36:14 -0000
Organization: Nextra UK
References: <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com>
NNTP-Posting-Date: Tue, 3 Dec 2002 21:34:47 +0000 (UTC)
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
"John Fields" wrote in message
> What he's saying is that with his stupid way he needs a voltage
> source which can be adjusted to output precisely the current needed
> by the LED at some temperature, (ISTR something about 0.25% of
> something being thrown in there too...) and then that the LED's
> tempco will keep it constantly at that same brightness over a large
> temperature range. But if that doesn't work, then Harry suggests
> that a thermistor (either positive or negative tempco, he's not
> sure) be used to _make_ it work. The original premise was that all
> the LED's in an array should be driven by a constant voltage source,
> so that means that for a 200 LED array each LED would _have_ to be
> driven by its own 1/4% voltage source and thermistor. Patently
I must admit that such an approach is somewhat problematical and may have
been postulated without too much understanding of the principals involved.
I have seen commercial equipment that uses a similar(ish) approach and the
performance over any but the most limited temperature range is as appalling
as would be expected.
Hate to think what happens over the longer term - maybe nothing changes with
time as well as temperature !
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup