SMD LED's - Vf, If

[arhi]

I have bunch of SMD LED's (mostly green and red, few white and few blue ones).. some are 0.6 some 0.8mm

The problem I have is, I have no idea what the voltage dropout is for those, what is the optimal and what is the maximal forward current, how long I can drive them with maximal forward curent .. etc etc ..

Is there any way to measure this values (Vf I can probably measure with voltmeter but how to know optimal forward current) ? Is there "standard" for SMD LED's or trial & error is the only way to go?

 

[ronsimpson]

With out looking most small LEDs use a maximum of 20mA.

Go to digikey.com
Part number search window type in “LEDs”
Page down to Optoelectronics and click on LEDs -<75mA
You can select which type of LED to look for. Under Package/Case I selected 0805 just to pick a small SMT type. Click on Apply Filter.
I selected RED and Applied the Filter and now there are only 137 red 0805 LEDs.
To get to a data sheet faster I chose the Manufacture of Rohm.

At this point it looks like a RED LED needs 1.7 to 2 volts with a maximum of 20mA.
Select a part-number. Select Datasheets.

Now I see a datasheet for a series of Rohm LEDs in a small SMT case.

 

[arhi]

thankx, I'll try

 

[mvs sarma]

thankx, I'll try

But it would be safe to try at 60% or so of the max current
this would increase the LED life. If I were to do it I don't feed more than 10mA

 

[Hero999]

The shorter the wavelength the colour the higher the forward voltage will be.

Red will be between 1.7 to 2V.

Green will be between 2 to 3.3V depending on whether it's a blueish green or yellowish green.

Blue and white will be from 3 to 3.6V.

The forward voltage also varies depending on the current, for example a red LED might have a Vf of just 1.6V at 500:mu:A and 1.9V at 20mA.

 

[Speakerguy]

The shorter the wavelength the colour the higher the forward voltage will be.

That is an excellent way to remember. I always get red and green confused.