LEDS Probs

[joecrack57]

ok i just some bought leds of mouser and for some reason every time i test them with the psp battery they get fried the only way i can get them to work is if i use a 10ohm resistor on it and not only that the green and yellow leds still fry the only ones that don't need the 10ohm resistor are the red leds and when i use the 10ohm resistor on the blue it works fine, can anybody out here tell me what i'm doing wrong cus i want to do blue and red led swap for my cousin and i don't want them to fry while he plays, any help would really be appreciated.

[everlasting_will]

Put resistors before or after every led. I think there is a tool in this web for calculating the proper resistor. Anyhow look at the datasheet of each led cause each color works at different voltage. Most of the leds work fine with 20mA of current going through them. So if you are attaching to the psp battery which is 3.6 volts you have to do the following calculation:
3.6 = 20mA*Resistor + LEDvoltage;
for example if your led is green and we suppose that it works fine with 2.5V (read the datasheet):
3.6=20mA*Resistor + 2.5;
1.1=20mA*Resistor;
Resistor = 0.055*1000 = 55ohm;

Also if you are going to work with common resistors you won't have to do the following calculation but if you are going to use smd resistors you have to be sure that the resistor is capable to drive away enough power. The power dissipation it's going to drive away the resistor can be calculated as:
P=V*I; so V was 1.1 volts and I was 20mA;
P=22/1000=0.022W so you need a resistor capable to drive away that power.

I think that typical power dissipation for smd resistor are (depending on the size):
size 1206 -> 1/4 W
size 0805 -> 1/8 W
size 0402 -> 1/16 W

but check it cause i am not sure;

[crashman2k7]

ok
blue dont need resistor neither does green
red need at lease a 10 ohm resistor
so b4 any red led is connected to a power source put a 10ohm resistor

trust me i put a red led direct to the 2.3 volt near the top fuse and it blew up like a lil fire cracker! tought i lost a eye wid that 1

[joecrack57]

thanks for ur guys help go it to work