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Topic: Power Supply For Arduino (Read 626 times) previous topic - next topic

NobleNoob

Oct 16, 2012, 12:11 am Last Edit: Oct 16, 2012, 12:20 am by NobleNoob Reason: 1
Can an Arduino 2560 run comfortably at a regulated 12V?

I would like to power my projects with a converted ATX power supply and power the Mega from the 12V rail.

Or do I need to step it down to 9V

I read somewhere the upper voltage limit was 12V

Dropping to 9V adds more components, cost, failure points to my project.

Thanks In advance....

johnwasser

If your ATX power supply has regulated 5V you can connect that to the +5V pin.

The regulator on the Arduino can deal with voltages up to about 18V, if I recall correctly.   At 12V the regulator is dumping 7/12ths of the power as heat so it tends to get very hot.
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NobleNoob

#2
Oct 16, 2012, 04:21 am Last Edit: Oct 16, 2012, 04:26 am by NobleNoob Reason: 1
I thought I read somewhere that the minimum voltage should be 6.35 volts to correctly operate the integrated reglulator.

Given that you must obviously know what you are talking about, I must assume that you were talking about making the 5V supply connection to the 5V Pin instead of the dc power jack and I further assume that the 5V Pin does not use the integrated regulator?

Is this correct?

by connecting this manner will I still have 3.3V?



CrossRoads

Don't supply 5V to the 5V pin witout adding a diode from there to the Vin pin.  Apparently the latest regulators are sensitive to being reverse driven.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

johnwasser


I must assume that you were talking about making the 5V supply connection to the 5V Pin instead of the dc power jack and I further assume that the 5V Pin does not use the integrated regulator?

Is this correct?


That is correct.  That's why I said "If your ATX power supply has regulated 5V you can connect that to the +5V pin." :)

The problem of the regulator being sensitive to reverse voltage is news to me but CrossRoads is a trained electronics engineer so I trust his statement.
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NobleNoob

hmm, ok, well reverse is what cause both of my auto accidents lol...

could you tell me what kind of diode I need?

And....

How to wire it up?

I am so sorry to be a noob, but I am so happy cause you guys ROCK SO HARD!

I love the idea of using the 5V rail off the ATX supply for the arduino, cooler is better :)




CrossRoads

http://www.ti.com/lit/ds/symlink/lm1117-n.pdf

See section 4. 1N4002 from 5V to Vin.

Has been discussed in the forum as well.

Another manufacturer's data sheet went into it further. 
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

retrolefty


http://www.ti.com/lit/ds/symlink/lm1117-n.pdf

See section 4. 1N4002 from 5V to Vin.

Has been discussed in the forum as well.

Another manufacturer's data sheet went into it further. 


Another valid argument against powering an arduino via it's shield 5V pin is that because there is no Vin voltage being applied the auto-voltage selector circuit will be gating the USB's +5vdc voltage source onto the board's Vcc bus anytime you plug in the USB cable to the PC. This effectively means your external regulated +5vdc voltage source will be 'hardwired' to your PC's USB +5vdc voltage source. As those two voltages will never be exactly the same value at all times that can allow 'reverse currents' to flow where it was never designed to and can effect the both regulators feedback circuit. It's just not a good engineering practice to wire too different voltage sources together without proper isolation between the two sources.

But of course people have been powering their boards with external regulated +5vdc voltage sources via the arduino 5V pin and using the USB connection without experiencing any problems, so it's really a personal choice and will most likely never result in the burning down of one's home.  ;)
Lefty

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