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Article #242

Re: Best way to power array of LEDs?

#242
From: Lizard Blizzard
Date: Mon, 07 Oct 2002 23:56
34 lines
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DaveC wrote:
> On Fri, 4 Oct 2002 10:51:27 -0700, Lizard Blizzard wrote
> (in message <ankkbu$lv9i$1@hades.csu.net>):
> 
> 
>>Using a lamp to serve as a more or less constant current 'ballast' is a 
>>good idea, but if it is run at anywhere near normal brightness, the 
>>lamp's lifetime will be short in relation to the LEDs.  And of course 
>>when the lamp goes open, the LEDs no longer get current.  So it would be 
>>much wiser to use it at much lower than normal brightness so that the 
>>lifetime is extended considerably, comparable to the LEDs.
> 
> 
> But then if it's not running at temperature, you don't get the temp/current 
> regulation that is the main reason for using it. Yes?

The lamps have been used as a variable resistance ballast since HP built 
their first product, the HP 200 audio oscillator.  The bulb doesn't have 
to glow to exhibit positive temperature coefficient.  I've built Wien 
Bridge oscillators using a lamp for variable negative feedback, and the 
lamp doesn't glow.

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From: Lizard Blizzard <NOSPAM@rsccd.org>
Newsgroups: sci.electronics.components,sci.electronics.design,alt.engineering.electrical,aus.electronics,sci.electronics.repair
Subject: Re: Best way to power array of LEDs?
Date: Mon, 07 Oct 2002 16:56:44 -0700
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