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shermaine · 19th September 2007, 05:44 AM

how to determine the forward bias voltage for red, green, blue led?

Papabravo · 19th September 2007, 06:15 AM

A resistor, an ammeter, a power supply and a voltmeter.

Gayan Soyza · 19th September 2007, 06:23 AM

Take a variable DC supply that starts from about 1.5V & give to the LED. You won’t see it lights up. Now slowly increment the voltage & see what voltage the LED starts to lights up. That’s the voltage you looking for.

audioguru · 19th September 2007, 02:11 PM

LEDs operate with current, not voltage.
You must use a current-limiting resistor in series with the LED so you don't use too much current.
Then simply measure the voltage across the LED.

Hero999 · 19th September 2007, 10:38 PM

Simply connect the LED in series with a resistor and connect it to a power supply and measure the voltage across the LED.

kchriste · 20th September 2007, 05:26 AM

The easiest way is to read the data sheet.

audioguru · 20th September 2007, 02:18 PM

Quote:

Originally Posted by kchriste

The easiest way is to read the data sheet.

It will say the range of forward voltage. If it is a red LED it will say "minimum= 1.5v and maximum= 2.4V at only 20mA".
You must measure it to know what is the actual forward voltage.

Optikon · 20th September 2007, 04:13 PM

All data @ ~ 10mA forward current

I.R. = 1.40V
Red = 1.65V
High-Efficiency RED = 2.20V
Pink = 2.00V
Orange / Amber = 2.10V
Yellow = 2.20V
Green = 2.20V
High-Efficiency Green = 2.30V
Blue = 3.10V

These are *TYPICAL* values.
These values will differ from vendor to vendor.

**Krumlink** · 20th September 2007, 04:15 PM

Ive never seen a pink LED. What are the voltage ratings for Organic LEDs?

Ambient · 20th September 2007, 04:53 PM

The LED's I got from moreleds.com are:

Blue: 3.3V
White: 3.3V
Red:1.7V
Green:1.7V

all were ultrabright LED's, more than 5000mcd.

The other site to check out is: http://alan-parekh.vstore.ca/index.php/cPath/4

Optikon · 20th September 2007, 08:05 PM

Quote:

Originally Posted by Ambient

The LED's I got from moreleds.com are:

Blue: 3.3V
White: 3.3V
Red:1.7V
Green:1.7V

all were ultrabright LED's, more than 5000mcd.

The other site to check out is: http://alan-parekh.vstore.ca/index.php/cPath/4

Interesting.. what current were they measured at?

audioguru · 20th September 2007, 09:01 PM

Cheap LEDs are very bright when the plastic case makes a very narrow angled focussed beam from a dim old LED chip.

Good LEDs are wide angle and very bright.

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19th September 2007, 05:44 AM	(permalink)
shermaine	leds how to determine the forward bias voltage for red, green, blue led?

19th September 2007, 06:15 AM	(permalink)
Papabravo	A resistor, an ammeter, a power supply and a voltmeter.

19th September 2007, 06:23 AM	(permalink)
Gayan Soyza	Take a variable DC supply that starts from about 1.5V & give to the LED. You won’t see it lights up. Now slowly increment the voltage & see what voltage the LED starts to lights up. That’s the voltage you looking for. __________________ Gayan My Website http://gsmicro.blogspot.com/

19th September 2007, 02:11 PM	(permalink)
audioguru	LEDs operate with current, not voltage. You must use a current-limiting resistor in series with the LED so you don't use too much current. Then simply measure the voltage across the LED. __________________ Uncle $crooge

19th September 2007, 10:38 PM	(permalink)
Hero999	Simply connect the LED in series with a resistor and connect it to a power supply and measure the voltage across the LED. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez And http://www.silicontronics.com, same screen name as here.

20th September 2007, 05:26 AM	(permalink)
kchriste	The easiest way is to read the data sheet. __________________ --- The days of the digital watch are numbered. ---

20th September 2007, 04:13 PM	(permalink)
Optikon	Some typical forward voltages for various LEDS All data @ ~ 10mA forward current I.R. = 1.40V Red = 1.65V High-Efficiency RED = 2.20V Pink = 2.00V Orange / Amber = 2.10V Yellow = 2.20V Green = 2.20V High-Efficiency Green = 2.30V Blue = 3.10V These are TYPICAL values. These values will differ from vendor to vendor.

20th September 2007, 04:15 PM	(permalink)
Krumlink	Ive never seen a pink LED. What are the voltage ratings for Organic LEDs?

20th September 2007, 04:53 PM	(permalink)
Ambient	The LED's I got from moreleds.com are: Blue: 3.3V White: 3.3V Red:1.7V Green:1.7V all were ultrabright LED's, more than 5000mcd. The other site to check out is: http://alan-parekh.vstore.ca/index.php/cPath/4

20th September 2007, 09:01 PM	(permalink)
audioguru	Cheap LEDs are very bright when the plastic case makes a very narrow angled focussed beam from a dim old LED chip. Good LEDs are wide angle and very bright. __________________ Uncle $crooge