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Yes.
The difference between the supply voltage and the sum of the LED forward
voltages divided by the LED current is 90 ohms and you have chosen the
nearest standard 5% value, 91 ohms. Well done.
If you can't get that relatively hard-to-find value, use two 47 ohms
(much more common) in series, or 100 ohms will work okay with no
perceptible difference in brightness.
All that's left to do is determine the wattage required for the resistor
to dissipate, and that'll be the difference between the supply voltage
and the sum of the LED forward voltages _multiplied_ by the LED
current,
(12V-10.2V)*0.02A = 0.036 watts
so a 1/4 watt resistor will be fine.
I bought a couple dozen blue LEDs and I've found that every one of
them that I've taken out of the package is intermittent. And it's
really strange, too. I crank the PS up to 1.5V and the LED starts to
draw current, maybe a few mA, but the current is really erratic, I
can't get a stable reading. If I go up to 3.5V at 25 mA, sometimes
the LED will light steady, sometimes it will blink, maybe a few times
a minute, maye less, once every few minutes I've checked at least 6,
probably more, and they're all like that. Bad news. Sucks.
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###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it:
http://physics.nist.gov/cuu/Units/binary.html
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