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How much current can I draw from the 5v header pin?


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#1 samjones

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Posted 28 February 2012 - 05:02 AM

I am looking at: http://www.netduino....oplus/specs.htm and don't see the answer to this question: How much power can I draw from the on 5v header? (I guess the same goes for how much can I draw from the 3.3v header?) I see the specs say "microcontroller max current: 200 mA total" Does that mean the whole netduino plus board will never draw more than 200 mA ? Thanks!

#2 Chris Walker

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Posted 28 February 2012 - 05:14 AM

Hi samjones, You shouldn't try to draw more than 200mA total from the pins of the SAM7X microcontroller. The 5V and 3V3 headers can provide quite a bit of power for you. I'd recommend staying at 200mA or below on them...but technically the Netduino can provide up to 800mA total. The more power you draw, the most energy is wasted as heat on the LDO power regulators. Chris

#3 samjones

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Posted 28 February 2012 - 05:28 AM

Chris, I understand the 200mA limit on the io pins. It sounds like on the 5v header pin, I could do 200-350mA ? (e.g. to power a small wifi bridge) ? As I understand it, the netduino plus board itself max draw is 200mA. So is the following warm? 9v, 600mA PSU to netduino input 350mA load on 5v header pin Couple small devices hanging off of other pins, drawing 50-150mA total Warm?

#4 Chris Walker

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Posted 28 February 2012 - 05:33 AM

Hi samjones, The best thing to do is test your components...and then see if you're comfortable with the temperature. The LDO power regulators are 800mA, but I'd recommend staying at <=500mA total. Also, remember the the 5V power regulator is discarding 4V (using a 9V power supply) as heat...so you might want to consider using a 7.5V power supply instead. Or provide 5V regulated power to the 5V power pin directly. Chris

#5 samjones

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Posted 29 February 2012 - 02:07 AM

Chris, Thank you, will work in that direction! Question: The netduino is speced at a 7.5v min input. If I use a 5v or 6v regulated psu, can I put that into the barrel connector?

#6 Chris Walker

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Posted 29 February 2012 - 02:28 AM

Question: The netduino is speced at a 7.5v min input. If I use a 5v or 6v regulated psu, can I put that into the barrel connector?

If you use a 5V regulated power supply, you can plug it directly into the 5V pin header. You need a bit more than 6V on the power supply for the 5V LDO power regulator to output 5V.

Chris




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