newbie question

[raphaelriv]

hello all, sorry for the newbie question but this is just to get something clear:


this website: https://www.iguanalabs.com/1stled.htm

states that you must use a resistor with an LED to not burn it out. However if I use this LED:

Digikey Part number: 67-1131-ND
Product Photos SSL-LXA227ID-5V
Standard Package 1,000
Category Optoelectronics
Family LEDs - <75mA, Discrete
Color Red
Lens Style/Size Round, 1.8mm
Millicandela Rating 8mcd
Voltage Rating 5.0V
Wavelength 635nm
Current - Test 20mA
Viewing Angle 60°
Lens Type Diffused, Red Tinted
Luminous Flux -
Catalog Page 2412
Other Names 67-1131


and hook it directly to a power supply and i fixed the voltage at 5volts the LED worked and the current it pulled was 0.012Amps. It didn't burn out or anything.

The formula in other tutorials to find the appropiate resistors are:

Vled + Vresistor = Vsupply

Vresistor = V supply - Vled

Vresistor = If x Rresistor

Rresistor = Vsupply - Vled / Ir

----------------------------------------------------------------

the question is should I be using a resistor? with this particular LED ? from what i read i can see that the answer is yes to limit the current to a safe value. But then the Foward voltage spec seems to high to take it into account. 5volts?

i'll appriciate some advice. thanks

 

[kjennejohn]

Hi. This LED has a resistor built into it that sets it for use in a 5V circuit. You can't overdrive it unless you subject it to a higher voltage that leads to a current greater than its rated max. You can typically use these with a slightly higher voltage, like up to 12V, where it gets real bright, and lower voltages like 3.3V, where it's dim. The tipoff is the "-5V" at the end of the part number. A 12V part will have "-12V" at the end, etc. This isn't true for all LEDs, however. You'll have to check the data sheets. The interesting thing is, I couldn't find the data sheet using the given part number at the manufacturer's site. Go figure!

Later!
kenjj

 

[raphaelriv]

re:

where did u ended up finding the datasheet, i tried mfg and googling it and nothing came up