G>

How about link 8 of them serially, 8 LED * 2.2V(Vfwd) = 17.6V

;-)

Peter Chong

http://ww.ezxmlwizard.com

"Dennis Heidner" <[log in to unmask]> wrote in message
news:01c0d9ee$b691dbb0$031e82c0@bigbird...
> Rich,  I haven't seen the reply that Steve has made.
>
> The LED should have a published spec for the  voltage drop (Vfwd) and
"MAX"
>  voltage drop.  The term forward is general added to indicate that the
> device is wired and biased so that it should operate (light up).  It will
> also have a spec for the current that will flow when the device has the
> correct voltage across it.  We can call that Ifwd.
>
> Your resistor value should then be      Rdrop = (17.5  - Vfwd)/Ifwd
>
> Or using the value that Steve provided (820 ohms).
>    Vfwd is typically 2 volts -- for most LED's,  (higher for some laser
> devices and the new super bright LED's)
>
> 820 = (17.5 - 2.0)/Ifwd   or Ifwd = 15.5/820 = (rough) 19 milliampere's
> current.
>
> The resistor will see about a 1/3 watt heat generation.
>
>
>

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