LED Voltage

[ragtop]

Anybody know what voltage your typical computer case LED's run at?? (power, IDE activity, etc. that are mounted on the front of the case).

Just curious 'cause I have a bunch & was thinking of using them for a non-computer related project.

[diesel8859]

It seems to me from some electronics class many moons ago that diodes needed .7 volts to operate. As such since LED is light emitting diode, it should be .7 volts, and those are directional.

[Da_Flea]

My computer one runs at 5 volts.... we *deleted* rigged a light on a small 6v battery before but it only lasted 2 weeks with that extra voltage.....then it blew and wouldn;t light...so good luck....kinda curious whay u lighting up?



[This message has been edited by socalgal (edited 06-02-2001).]

[Andy_L]

"we *deleted* rigged" Could you say anything more offensive without trying?? http://www.sysopt.com/forum/faq/faq4.html#Pol5


[This message has been edited by Andy_L (edited 06-02-2001).]

[This message has been edited by Andy_L (edited 06-02-2001).]

[This message has been edited by socalgal (edited 06-02-2001).]

[Bsdboy]

Most LED's run in the 1.7~3.0v range you can use a higher voltage with a series restor(supply voltage minus the LED voltage divided by the LED current).

Bsdboy

[Graham]

ragtop,
Bsdboy is right, somewhere from 1.5 to 3.0 volts normally, ultra-bright and some of the newer colours use up to five volts.


G

[Bsdboy]

Yes ultra brights and blue ones are in the 3~5v range but standard ones are happy at 2v even 1.5v Led's can take 2v max,it might shorten their life a little but they should last a while.

Bsdboy

[Richard_Cranium72]

The voltage varies greatly depending upon many factors..

Mfg name Chicago Minature quotes 1.7-5vdc and 20ma current draw

Hewlett Packard quotes 1.7-2.2vdc and a 20ma current draw

The indicator as I intrepret it ,, you can run the LED's as low as 10ma, but the overvoltage is limited to about 10% of rated voltage..

Note that LED's are polarity sensitive, backwards wiring will not damage them, they just will not burn..

DrVette

Source;

Allied Electronics Catalog #980
www.allied.avnet.com (http://www.allied.avnet.com)

[Andy_L]

I dont mean to make the post contraversial either, and I understand that some phrases are natural and innocent, but at the same time, I'm sure that no one here wants to make anyone feel unwelcome or uncomfortable. BTW, I drilled out a minimaglite so I could use LEDs in it instead of bulbs, and 3 volts seemed perfect.

[Bsdboy]

Andy_L cool idea about the mag light but why?
It cant put out much light.

Bsdboy

[ragtop]

Decided to give them a try. I had a few red, yellow, and green ones I pulled from old cases. The red ones worked with one AA battery (1.5V), but the yellow and green ones took two bateries (3.0V) before they would light up.

[Etruscan]

Uh.. just thought I'd add my two cents since only part of the right answer appear in the same place on the thread. diesel|8859 amd Bsdboy are right. No matter what voltage you apply to the circuit there will be a .6 voltage drop over the LED in forward bias. The rest of the voltage will appear as voltage drop in the remaining resistance in the circuit. What is important is the current through the LED. You must select your resistor to achieve the right current with the voltage applied. Many LEDs work in a range of 5 to 60 milliamps. If you go over that by much, say 150 milliamps, chances are, you are going to damage the LED. Check the current ratings of the LEDs you're using or experiment for best results.

[DanU]

LED's aren't really specified by their voltage, they are specified by their current. The voltage itself can fluctuate due to any number of factors.

Power supplies are normally voltage source devices, with little current control. Because of this, you are going to have to do some design work to limit the current to a safe value. This usually involves just putting a properly sized resistor in series with the LED.

Let's do an example... I'll assume you already know Ohm's Law and Kirchoff's laws. If not, you can look them up on google.com.

Say you have a red LED. These typically run at about 10 milliamps, 1.4 volts. You want to hook it up to a 5V power supply. How many ohms does the series resistor need to be?


+5V O----/\/\/\/\-----|>|------O GND

The voltage across the resistor is 5 minus the voltage of the LED, or 5 - 1.4 = 3.6V. You want the resistor to pass 10 milliamps, so divide 3.6V by 0.01A and you get 360 ohms for the resistor.

[Andy_L]

In the Army, you can't use a white light in the field at night, and it seems like you always lose the colored lens covers. The LEDS are also free, lol. They put out as much light with the LED as with a standard bulb and a lens cover, because of the focusing mirror.

[ragtop]

Seems like a wide variety of opinions. Maybe I'll get out the ol' volt meter and see what the LED's are running at on one of my systems.

Too bad about that one insensitive comment above, I sure didn't think this would be a controversial topic.