Question 12v to power 3v LEDs

loxy061

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Aug 12, 2015
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Hi, I want to use those 2 pronged 3v leds in my car, however I have trouble understanding how to choose a right resistor, and also I am worried that resistor will get very hot and make a much higher power consumption. So it would help a lot if anyone can spare a little time and explain this to me. Thanks in advance 😁
 
You can use resistors....but the problem with that is....75% of your power is going to go to the resistors as heat as you said.

If you use a larger resistor (not larger in ohms...larger in watts)...it won't get as hot but still that's not ideal.

What I would do is use a 3V voltage regulator.

Here is one.

https://www.newark.com/rohm/ba30dd0t/ldo-fixed-3v-2a-40-to-125deg-c/dp/01AH6347

There are others.

With this particular one you can input up to 25 volts....it will output 3 volts at up to 2 amps.

Jay
 

hotaru.hino

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Sep 1, 2020
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I believe a "3V LED" just means you need at the minimum 3V (forward bias voltage) or higher to turn it on. Diodes need a minimum amount of voltage before it turns on and allows current to flow. The thing is once it reaches that minimum voltage, the amount of current it lets through ramps up dramatically with more voltage, and that's what kills the diode.

While getting a voltage regulator that closely matches the forward bias voltage would at least prevent the LED from instantly blowing up, it can still draw enough current to be unsafe or shorten the LED's life. You'd still need a resistor to limit current, but something like 1K is probably enough. But I'd suggest getting a variety of resistances or even a potentiometer and play around with how much resistance you need for the brightness you want.

See https://electronics.stackexchange.com/a/245458
 

loxy061

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Aug 12, 2015
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Thanks everyone but its kinda difficult to use anything else than a resistor because the space is very tiny, I wonder is there a 12v variant of those leds, I was looking on the Internet but could find anything...
 

hotaru.hino

Prominent
Sep 1, 2020
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Thanks everyone but its kinda difficult to use anything else than a resistor because the space is very tiny, I wonder is there a 12v variant of those leds, I was looking on the Internet but could find anything...
Getting an LED driver like what @jay32267 linked is the best solution. Otherwise, it's still not a good idea to run bare LEDs (I'm assuming it's a bare LED with nothing else in it) because of the potential they have to draw way more current than they should for practical operation.
 

Mtop

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Nov 21, 2019
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E=IR E is volts, I is current, R is the resistance
10k in series with 10k across 12v = 6volts across each resistor .6ma current and 6 milliwatts.
10k in series with 5 k in series with another 5k =20k total with 3v across a 5k resistor. If the resistors are hot - dont put in the gas tank!
 

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