Date:         Tue, 18 Sep 2007 13:54:36 -0700
Reply-To:     David Kao <dtkao0205@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Kao <dtkao0205@YAHOO.COM>
Subject:      Re: LVC adding LED interior lighting
Comments: To: Mike S <mikes@FLATSURFACE.COM>
In-Reply-To:  <20070918193201.2104D1165C3@hamburg.alientech.net>
Content-Type: text/plain; charset=iso-8859-1

That's false.

Power dissipated by each LED is the current multiply the voltage drop
across. By connecting LEDs in serial you force them to all operate at
a same current but different voltages. This would be a false design if
all LEDs are different. One LED may be required to operate at 15MA but
another may be 300MA.

If LEDs connected in serial are same LEDs, by connecting them in serial
you allow them to operate at a same current, which is fine, but still
each one is forced to operate at a different power level unless every
single LED is identical. In reality if the LEDs are not produced from
a same silicon wafer their voltage drop across the PN junction will be
different. As a result you will find the brightness from each LED,
in serial, different. That's still fine if the difference is small.

If somehow one of the LED is shorted out, because of vibration of your
westy, or just a simple internal failure that usually happens to diodes
as a short first, your other LED will be instantly destroyed too. If this
very likely if the LEDs are set to operate at a high power (brightness)
level. They are diodes and they generate heat. They will burn out too.
When one burns out the other goes with it. An LED burns of by melting
its PN junction to become a shorted diode first.

As I said you can do it but it's not an ideal design. See this web:
http://www.chesmontastro.org/?q=node/526

If you want to connect LEDs in serial you can under power a bit to keep
them safe. But you won't get all the brightness.

David


--- Mike S <mikes@FLATSURFACE.COM> wrote:

>
> LEDs run on current, not voltage. When connected in series, they will
> always operate at their own individual voltage drop. That is necessary
> and desired.




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