I have this 3mm LED with a 150ohms on the positive side http://www.eled.com/product.asp?catalog_name=LEDs&category_name=&product_id=E7104QBC-D I was wondering if i can power this LED by using the 5v on my 4pin molex on my PSU?
That resistance is a bit low, but you should be ok. Ideally you want 250 ohms to match it to its rating of 20mA.
assuming u are only powering one LED and also assuming the forward voltage is no less then 2v then 150 should be fine if the forward voltage is 2v and the mA is 20mA then (5-2)/.02 = 150ohms that is to provide maximum voltage dont forget there are some minor fluctuations in the PSU output Voltages and also differences in LEDs in theroy 150ohms is okay it should be okay though its the exact value u need
But it's a 3.5v blue, so 150R on 5v will give 10mA with bren2's formula, safe as houses, but you could go as low as 75R for maximum brightness at 20mA.
oh i didnt see that.. thats y i used 2v so (5-3.5)/.02=75ohms thnxs for pointing that out cpemma didnt catch the forward voltage hopefully that helps sojumk
