RE: White LED Lighting... was RE: Re: ADSL vs Cable

["Jon Whiten" <jon@xxxxxxx>]

Keith,

In principle you are right, however, with the white LEDs the variance
in
forward voltage is large enough to kill the odd LED if you get LEDs
from
both extremes in the same 3-way chain.  In terms of reliably driving
these
LEDs it is therefore better to drive them from a constant voltage
(regulated) source with a series resistor for each LED.

Also be very careful that you don't kill them when soldering - not sure
about the wire-ended ones but I do know that the SMD equivalent is
sensitive
to the exact reflow solder profile.

I have seen units made from 32 chains of 3 LEDs (96 total) just go-out
before my eyes - quite an expensive mistake!

Regards,

Jon
http://www.whiten.co.uk/


-----Original Message-----
From: Keith Doxey [mailto:lists.diyha@xxxxxxx]
Sent: 24 April 2002 13:19
To: ukha_d@xxxxxxx
Subject: RE: White LED Lighting... was RE: [ukha_d] Re: ADSL vs Cable


If you put 3 LEDs in series you only need one resistor per 3 LEDs

Power disipated (WASTED) by the resistor is also reduced to a third as it
is
only dropping 3v now.

also using the series method you are lighting 3 LEDs with only 20mA
compared
to 60mA if driven individually.

Total power consumption is now 33% of what it would have been.

Smaller transformer + thinner wire + less power = lower running costs =
more
money left for toys :-)

Keith
www.diyha.co.uk
www.kat5.tv



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