Or, maybe this explains why all the LED's on the series 70 power supplies
had trouble?
Larry A. Barnes
Systems Administrator - HP3000
Coldwater Creek Inc.
http://www.coldwatercreek.com
-----Original Message-----
From: John Hurt [mailto:[log in to unmask]]
Sent: Thursday, May 10, 2001 2:56 PM
To: [log in to unmask]
Subject: Re: [HP3000-L] OT: Electronic Circuitry Questions
is this how nuclear meltdowns start?
-----Original Message-----
From: HP-3000 Systems Discussion [mailto:[log in to unmask]]On
Behalf Of Wirt Atmar
Sent: Thursday, May 10, 2001 4:50 PM
To: [log in to unmask]
Subject: Re: [HP3000-L] OT: Electronic Circuitry Questions
Steve writes:
> If in doubt, more resistance => less current => less chance
> of burning out your LED--especially if you wire it in backwards.
Everything Steve writes in regard to wiring LEDs is correct, with the
exception of this very last phrase. If you wire an LED backwards, nothing
much of anything happens. It doesn't glow, but it isn't harmed either.
LED emission occurs when the p-n junction depletion region is squashed to
essentially zero width by the action of the forward biasing circuit that
Steve describes. Once the depletion region is squashed, the free flow of
majority charge carriers into the alternate doping regions is allowed,
thereby greatly increasing the probabilities of hole-electron annihilations,
resulting in the emission of one photon with each hole-electron pair
annihilation.
If the same LED is reverse-biased, all that happens is the intrinsic
depletion region is enlarged, greatly decreasing the chance over that of an
unbiased LED that majority carriers will ever see each other, and thus glow
spontaneously. So long as the reverse bias is less than the dielectric
breakover of the mobile charge depleted region -- and it always will be in a
simple circuit such as Steve describes -- no harm can come to a
reverse-biased LED.
I know everyone is going to sleep easier knowing this stuff.
Wirt Atmar
* To join/leave the list, search archives, change list settings, *
* etc., please visit http://raven.utc.edu/archives/hp3000-l.html *
* To join/leave the list, search archives, change list settings, *
* etc., please visit http://raven.utc.edu/archives/hp3000-l.html *
* To join/leave the list, search archives, change list settings, *
* etc., please visit http://raven.utc.edu/archives/hp3000-l.html *
|
