overpowering a LED

hi

I want to create a bright flash. I have a 80.000 mcd 10mm LED, and I really want to get the most out of it. The correct setup is a 47[ch937] R with the 5v from the arduino, but I would like to get the most out of it. Since it's just a 5ms on / 500ms off cycle I am hoping I can allow myself to "stress" the LED and get some more brightness.

Any ideas?

thanks

fubbi

Try it, it will get hot very quickly if overpowered, and then will die in less than 5 seconds.

The correct setup is a 47[ch937] R with the 5v from the arduino

:o

lol! what?

The correct setup is a 47[ch937] R with the 5v from the arduino

No it’s not the correct setup. You are frying your arduino with that.
Assume 1.8V across the LED, then 5-1.8 = 3.2V across a 47R resistor gives 80mA from the arduino pin, which will kill your arduino over time.

You have to power this LED with a transistor.

Now your question is how much more than this can the LED take if it is pulsed on a 1:100 duty cycle. The answer is in the LED data sheet.

Hi

It's just a normal LED, not a high power one. I am confused now.

My resistor was based on 5V source voltage, 3.6V diode voltage, 30mA forward current

(5 - 3.6) / ( 30 / 1000 ) = 46.6 ohms

Wrong?? I dont want to kill my arduino!

http://www.produktinfo.conrad.com/datenblaetter/175000-199999/181154-da-01-en-LED_KLAR_10MM_WEISS_LED_10_80_000W.pdf

You're already stressing the LED - 30mA is the maximum rating.

You're already stressing the LED - 30mA is the maximum rating.

No. In the data sheet Peak forward current is 100mA with a 1/10 duty cycle.

An interesting application note can be found here: http://www.stockeryale.com/i/leds/lit/app001.htm applicable to most of the LEDs

If you want a bright led buy a non difused led. If you want even brighter you could get a strobe ;)

Ohe thing you need to be careful about is making sure that the LED defaults to "off": while the Arduino is going through initialization, the digital pins will be set as inputs for a lot longer than 10mS. If you set up the LED for high current, and don't do something like putting a weak pulldown on the transistor base, it could turn on for long enough to fry the LED.