Re: Need an Ohm's law refresher

Thanks to all, but I think Kirb's idea of running 4 3.0v LEDs in series will
work perfectly with my 12v source.

I have no idea what current it supplies -- but the bulbs were most likely
25ma 12v grain-of-wheat bulbs.

Anyway I've just ordered some so I'll try hooking them up and see if
anything smokes or explodes ;-)

Thanks again guys.

Randy

"Wabajape" <dgfinck@xxxxxxxxx> wrote in message
news:1143671585.822955.67470@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
As Mark pointed out, it's the current that controls the LED brightness.
The voltage drop across it will be nominally constant (in normal
operating current ranges).
So a LED doesn't "draw" any specific current. You supply a current to
it (with a voltage source and a resistor to control the current) and it
lights, with a brightness dependant on the current going through it.
It may have a nominally rated current, which may be 28mA. But it
handle a range of currents.

However, I have a slight disagreement with Mark's calculation. I think
the LED's voltage drop should be subtracted from the source voltage in
the numerator of the calculation, givng R= (12V- 2.25V) / 0.28 ohms =
348 ohms. Pick your standard value, but then your resulting current
will be slightly higher or lower than the "nominal" 28mA.

Darren



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