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What resistor and method should I use to string 12 led's in parallel from a 5v source? Answered

I'm trying to figure out what resistor I should use to string 12 blue led's in a ring from a 5v source (like this except instead of 8, using 12: http://www.llamma.com/xbox/Mods/xbox_jewel_led_mod.htm). The specs that I have on the packaging of the led's are: MCD 4000~6000 and VF: 3.0v~3.2v. I read 2 different ways to do this, one (the easier way which I was leaning towards) was to use one resistor for the entire parallel series. The other way was to use an individual resistor for each led. What do you recommend. Can I get away with doing it the easy way, and if so, what resistor (ohms, wattage, and tolerance) should I use? Thank you.

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If the diodes are well matched, from the same batch and "identical", you MIGHT get away with a single resistor. I really don't like parallel driving LEDs but even some of the driver chip makers use it sometimes.

Steve

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gmxx

8 years ago

you're going to need 12  resistors. 100ohms each

Unfortunately you cannot do it the easy way. When connected in parallel the LED behaves in a strange way (related to the fact that they are current driven devices and not voltage dependant ones) - One of the LEDs will suck all the current and the others won't hardly light.

If they're 20mA each, you'd need a 0.240mA supply roughly 2V over the resistor(s).
One would need to handle ~0.5 W, 12 ~0.04W (smaller)
For a 2V drop: 8Ohm for 1, 100ohm for 12

L

Use this site that was listed in the link that you gave to figure it out for yourself.