Powering LED's through board

I'm running 12 LED's, each on their own pin through an arduino mega. Only 1 led will be on at any given time. Is it ok to power these through the board or would it be best to use a separate power supply?

The 50W type you certainly use would need a bit more amps than the board could provide. On the other hand, The board could be just suitable, who knows?

Using UNOs I'm not an expert regarding Megas but if You don't exceed the maximum current for each diode and not exceed the total output curent of the Mega, You're safe. An UNO supports 20 mA and the Mega likely has the same capacity. Check the spec!

You'll be OK with "regular little" LEDs and the proper current-limiting resistors, but just for completeness...

The power supply is only one factor/limitation, and there is no simple limit for the power supply. If you are powering through the on-board regulator it's heat/power limited, and the head depends on the voltage dropped across it (it will get hotter with 12V fed-in than with 7V fed-in) and the current through it as well as the ambient temperature.

The chip has a total maximum current spec of 200mA through the power supply pins, total (including whatever it takes to power the chip), and an "absolute maximum" of 40mA through any one I/O pin.

So... If your LEDs are running 20mA each and they "accidently" are all turned-on at once, you'll exceed the 200mA limit, but the odds are you're not going to instantly-fry the chip. (You probably[/] won't fry the chip if they are on "forever" but you would be exceeding the specs.)

Thanks! It sounds like I'm good just powering through the board

zwieblum:
The 50W type you certainly use would need a bit more amps than the board could provide. On the other hand, The board could be just suitable, who knows?

What 50W LEDs?
Were did that come from?
Tom.... :o

Good question. I assumed small, 20 - 40 mA, LEDs.
Actualy I did boost such diodes up to 50 Watts once! Dutycycle was one to a million, pulse length 1 microsecond.

You should have used liquid nitrogen cooling :slight_smile:

Maybe even higher powerdiscipation could have been allowed then. Unfortunately, or luckyly(?), nitrogen was not available.

Bluenick2100:
I'm running 12 LED's, each on their own pin through an arduino mega. Only 1 led will be on at any given time. Is it ok to power these through the board or would it be best to use a separate power supply?

You could run all 12 if you put enough resistor behind each one.

A red led with 1.8 forward voltage driven by 5V and having a 340 Ohm resistor would use ....

(5V - 1.8fV) / 340R = 0.009A = 9mA current.

12 of those won't break the board and still be decently bright.

Remember that components have tolerance on their spec. A +/- 10% 340R resistor may be as low as 306R which pushes the current up a little.

GoForSmoke:
Remember that components have tolerance on their spec. A +/- 10% 340R resistor may be as low as 306R which pushes the current up a little.

Bit hard to find a 340R resistor with a ±10% spec! :astonished:

Just as an example. I'm not a hardware expert, I try to buy 5% or better. That's gold band from back when the cost was gold band too.

Considering choosing resistors from standard values is bigger leaps, I don't have a problem with 10% as long as it doesn't let something be close to failure and then I choose the next safer value.