Date:         Wed, 19 Sep 2007 14:11:14 -0700
Reply-To:     David Kao <dtkao0205@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Kao <dtkao0205@YAHOO.COM>
Subject:      Re: LED Failure
Comments: To: Pensioner <al_knoll@PACBELL.NET>
In-Reply-To:  <HHEAJIOMDPBGGCKHACGJIEMICNAA.al_knoll@pacbell.net>
Content-Type: text/plain; charset=iso-8859-1

I actually don't have reliable data to say that the PN junction will
become open or short when an LED breaks down because of excessive heat
or power dissipation.

But it seems heat melts the PN junction to short it out first. It
then accelerates the melt down to burn it open. My SME 2400L audio
power amp broke down a few months ago. About half of the power transistors
are found to be short and open in many different PN and NP junctions.

I don't know. I think a short is a reasonable possibility.

David

--- Pensioner <al_knoll@PACBELL.NET> wrote:

> From days long gone by, I seem to recall that the most likely failure mode
> for diodes in general, of which category, LEDs are one instance, is to open
> circuit (burn open).  The lighting result in this case is the same as
> breaking the circuit.  All LEDs in the series branch switch to dark mode.
>
> Most diodes are limited by power dissipation.  When they get very hot they
> cannot dissipate the power across the junction and the junction temperature
> rises until the diode is destroyed (generally to open circuit).
>
> Now back to your regularly scheduled programming.
>




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