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5V/12V LED's - Any need for a resistor?
RandyT:
--- Quote from: ryguy on July 22, 2008, 12:39:39 pm ---They're 5V and 12V LED's.
Many thanks for the advice, sounds like I can keep it simple then!
--- End quote ---
Maybe, but...
According to the calculations, no resistor is required. However, I have seen folks recommend using a 1 or 2 ohm resistor in this case for a bit of extra security. The only time I have ever seen an LED used without a resistor is in those keychain single LED flashlights. Apparently, this is acceptable because batteries, by their nature, are current limited.
But the real question is what kind of LED are you attempting to use? Some will have a resistor built in and are designed to be used at the voltage specified without anything else. If you have a link to a spec sheet, you should post it to make sure.
RandyT
Blanka:
The LED is a load itself too. Otherwise it never could emit light. And current works on demand base, not on supply base. The LED just draws very little current. The computer has a switching powersupply so it adjusts very well to different loads and keeps the 5v very stable.
RandyT:
--- Quote from: Blanka on July 22, 2008, 01:51:38 pm ---And current works on demand base, not on supply base. The LED just draws very little current.
--- End quote ---
If you are referring to LED's in general, this statement is not true. An LED will keep drawing current until it pops. That's what the resistor is for
RandyT
Samstag:
--- Quote from: RandyT on July 22, 2008, 01:55:45 pm ---
--- Quote from: Blanka on July 22, 2008, 01:51:38 pm ---And current works on demand base, not on supply base. The LED just draws very little current.
--- End quote ---
If you are referring to LED's in general, this statement is not true. An LED will keep drawing current until it pops. That's what the resistor is for
RandyT
--- End quote ---
You are mistaken. Increasing the supply voltage is what increases the current. A resistor will also draw more current as you increase the voltage and will burn out if you exceed it's ability to dissipate the extra heat generated.
An LED just happens to be very poor at dissipating heat beyond it's design limits, but it still obeys Ohm's Law.
ryguy:
Thought it was too simple. I'm afriad there aren't many specs on the web page.
The 5V ones are from Ulimarc and go with the Ultralux buttons. They're the normal 5V ones and not the ultra bright 12V ones. The link is http://www.ultimarc.com/ultralux.html.
The 12V one came with the Happ trackball and sits underneath. It actually looks like a normal bulb so it may not be an LED. Can't find anything on this one.
A photo of them is......
Any advice welcome!
UPDATE - I've just read the bottom of that link page! It says no need for a resistor so have answered my own question, but still not sure on the 12V bulb!
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