low power LED less than 2ma

Nick · Guest

My search on mouser only gives alot of 2ma LEDS, but nothing less

http://www.mouser.com/index.cfm?&handler=data.listcategory&Ne=400&terms=low+current&Ntt=*low*%2b*current*&Ns=SField&N=430&crc=false

I want the lowest power LED or possibly an LED to run off the AC line.

I guess I cant run an LED off an 110VAC without a transformer and rectifier...

Nick

rnielsen · Joined: 23 Sep 2003 Posts: 852 Location: Utah

I, personally, haven't connected an LED up to 110VAC but I'm sure it's possible. I believe if you calculated your limiting resistor correctly that you could keep the current within specs. Also, you would probably need a diode in series with the LED to block the reverse voltage, the 'negative' half of the sine wave, so that the LED would not be destroyed.

Ronald

Mark · Joined: 07 Sep 2003 Posts: 2838 Location: Atlanta, GA

How bright does it have to be?
You can run less current and the LED will be less bright.

If a microcontroller is controlling it, you can also PWM the LED and get by with less current.

Guest · Posted: Tue Aug 10, 2004 10:24 am

Here is how you do it. Be careful of the reverse voltage on the LED. You may need a diode in series to prevent reverse breakdown. This works well. I have used it for many years. However this may expose the user / technician to the AC line directly. Be very careful in it's application!

Steve H.

[url]
http://ww1.microchip.com/downloads/en/AppNotes/91008b.pdf
[/url]

Gabriel Caffese · Joined: 09 Oct 2003 Posts: 39 Location: LA PLATA, ARGENTINA

Nick,

Just one question: If you want to connect the led directly to the mains, why are you searching for a low power one ?

Gabriel.-

Ttelmah · Guest

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

Have you considered using a neon bulb instead? They are inherently low current high voltage high reliability devices. Look for a NE2.
_________________
The search for better is endless. Instead simply find very good and get the job done.

djpark · Joined: 02 Mar 2004 Posts: 49

If you are trying to turn on an led as power indicator, I agree with SherpaDoug that neon lamp is a better choice for that purpose.

But if you insist on led, you can connect a capacitor to drop voltage. Just using a resistor will require a big size resistor to dissipate the heat. The AC RMS current can be calculated using this formula.

Irms = Vac * (2 * pi * Freq * Cap)

I will add a 1K resistor to block the worst situation current rush. I used this for my night lamp using blue leds.

cbstieff · Joined: 09 Aug 2004 Posts: 7 Location: Kensington, MD

Just a note on LED selection. First I would choose the LED that produces the most Mcd per mA of current draw. 2ma LEDs typically produce less than 20 mCd of light. White LEDs are readily available that produce more than 10,000mCd at 20ma. The lightoutput of a LED is closely related to the current draw. the 10,000mcd rated LED will produce about 800mCd at 2ma or 16 times the amout of light of the 2ma rated LED.

Check out some of the high output LEDs available at:

http://www.superbrightleds.com/leds.htm

Nick · Guest

Thanks for the great info. I have learned more for this forum than I have from my classes. I'm thinking about pulsing the LED.

Nick