From: Lizard Blizzard
Subject: Re: Best way to power array of LEDs?
Date: Mon, 07 Oct 2002 16:56:44 -0700
References: <0001HW.B9C26E7400A7161B165FEAC0@news.covad.net> <firstname.lastname@example.org> <0001HW.B9C33DA500C07DD2165FEAC0@news.covad.net>
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> On Fri, 4 Oct 2002 10:51:27 -0700, Lizard Blizzard wrote
> (in message ):
>>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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