Led's And Resistors, Quick Clarification

[legit]

hey all,

so as i've researched things i've begun to realize one thing, i might not need a resistor for my LED, okay so i have a 12v LED and its rated at 30mA that means that if i put it on a 12v line then it shouldn't need a resistor, right? (12v - 12v = 0, 0/30 = 0, = no resistor?) also on the standard four pin connectors i think i've read somewhere that the red is 12v and the yellow is 5, is that right? thanks

- legit

[sykocus]

seems like something is wrong with your math, but i always refer to a led calculator. i like this one http://wolfstone.halloweenhost.com/TechBas...ed_LEDCalc.html

 

yellow is 12v and red is 5.

[legit]

thats where it gets foggy, every single LED calculator i've found says ERROR when i put in 12 v for both the Forward voltage and the line voltage,

why?

whats up with my math?

[sykocus]

do you really have a led that is 12v?

[kewlboxer2]

its probally a red led with a voltage of 1.2v

[hardnrg]

edit: you know what, i found out that LED's that are classed as 12V have internal current limiters, so no need for a resistor!

[legit]

http://www.radioshack.com/product.asp?cata...2D011&hp=search

it is red, and someone once told me that it does have a resistor in it, but i've never seen anything about that anywhere that i can see, so maybe theres something to that hardnrg

if i put 12v's of battery's to it and it doesn't burn out it should be fine right?

thanks

- legit

[hardnrg]

there should be something to it... i work in an electronics shop that sells, amongst other things, 12V LEDs

 

in our catalogue it says:

 

These LEDs are designed to connect across 12Vdc power supply rails. They have a 12V integral current limiting resistor, which means no external current limiter is required with a 12V supply.

[kobalt]

One way of knowing for sure if it's a 12V led, use a standard mobo battery and sit your led horseback on the battery one leg to the positive and one the other side, try it both ways, if if lights up, it's a standard led, if not it's either burnt or it's really a 12V led loll.

At least you'll know it's not a regular one

[Rabbit]

LEDs can be made with on chip resistors in them. Most dont however, thus their forward voltage is only two volts or so. If it says on the package that the forward voltage, rated voltage, or just voltage is 12V, then it would not need a resistor (most likely if it even says 12V on the package, it probably has it).

 

And your math is perfectly fine.