SMD LED's - Vf, If - Electronic Circuits Projects Diagrams Free

arhi · 13th June 2008, 07:23 AM

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 · 13th June 2008, 01:13 PM

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 · 13th June 2008, 02:44 PM

thankx, I'll try

mvs sarma · 13th June 2008, 03:18 PM

Quote:

Originally Posted by arhi

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 · 13th June 2008, 04:10 PM

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 500µA and 1.9V at 20mA.

speakerguy79 · 14th June 2008, 02:43 PM

Quote:

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.

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13th June 2008, 07:23 AM	(permalink)
arhi	SMD LED's - Vf, If 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? __________________ http://www.it4um.com

13th June 2008, 01:13 PM	(permalink)
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.

13th June 2008, 02:44 PM	(permalink)
arhi	thankx, I'll try __________________ http://www.it4um.com

13th June 2008, 04:10 PM	(permalink)
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 500µA and 1.9V at 20mA. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez