From: Watson 'Atto Parsec' Name
Subject: Re: Best way to power array of LEDs?
References: <0001HW.B9C26E7400A7161B165FEAC0@news.covad.net> <firstname.lastname@example.org> <email@example.com>
X-Newsreader: MicroPlanet Gravity v2.60
Date: Sun, 6 Oct 2002 07:00:53 -0700
NNTP-Posting-Date: Sun, 06 Oct 2002 06:52:57 PDT
Organization: InReach Internet
In article <firstname.lastname@example.org>,
JoeBloe@thebarattheendoftheuniverse.org talked about...
> On Fri, 4 Oct 2002 09:14:21 +0100, Keith Wootten
> Gave us:
> >In message <email@example.com>, "Wouter van Ooijen
> >(www.voti.nl)" writes
> >>>Have assembled an array of LEDs for use as a 3rd brake light in my car,
> >>>configured as 4 rows of 9 jumbo LEDs, as of yet unwired. Of course the power
> >>>supply will be 12 volts nominal (13.8 volts, maximum).
> >>>What is the best method to power these from an intermittent (whenever I press
> >>>the brake pedal) power source?
> >>The crucial point is that when you put a resistor and N LEDs in
> >>series, the LEDs will take roughly a constant voltage so all voltage
> >>variation from your battery will be over the resistor, thus causing
> >>current variation.
> >You can mitigate this to a useful extent by using a small filament bulb
> >instead of a resistor. The positive temperature coefficient of the bulb
> >will help to keep the current variation reasonable as the supply voltage
> >changes. The bulb should be selected to run at more or less normal
> >brightness at maximum supply voltage while passing maximum LED current.
> Well now. There's a nice, warm, cozy circuit box for ya.
Well, you've made a comment just as dim as the bulbs would be. Whether it
is a lamp or a resistor, or a transistor, the heat output for a given DC
voltage drop and current will be the same. Duh.
Laugh's on you.
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you put NOSPAM in the
Subject: line. alondra101 hotmail.com
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Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html