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I have a 12V 2.5 ampere Dc adapter.Can i use it to power arduino uno board? It says on the arduino website that i can use 9-12V and upto 1 ampere. I am concerned with current limit here..

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    Note that the higher the voltage, the hotter the voltage regulator on the Arduino will get. Arduino requires 5V, so anything above must be regulated to 5V with the linear regulator on board (LM7805?). – Ryan Griggs Dec 18 '15 at 18:21
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    If you go in through the barrel jack the power will be regulated. – dlu Dec 18 '15 at 19:36
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Don't worry about the current limit. The board will only draw what it needs. The spec is telling you that the board can draw as much as 1 amp, so in general the power supply should be able to supply that – more is no problem, but less could be if you have a lot of devices attached to the board that are drawing power as well.

As is pointed out in the comment above the higher the input voltage the more power the on-board regulator will need to dissipate (as heat). If you are using the barrel jack (which you should if you aren't providing power through an external regulator or other stable source) there is a diode (D1 in the reference design) in the input path and the MC33269D-5.0 regulator is spec'd with a max dropout voltage of 1.25 V so you will need an input voltage of at least 6.95 V (assuming a 0.7 V drop across the diode).

  • So i shouldn't worry about 2.5 amperes? everything else is ok. – Awais Saifi Dec 19 '15 at 8:09
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    Not at all. The 2.5 A is a capability of the power supply. I can provide up to 2.5 A if you need it, but it will not "force" more current into the load than the load is asking for. Think about it as being like a water pipe – a larger pipe has the capability of moving more water than a smaller one, but the amount of water that flows is determined by the valve at the end. All other things being equal (which they never are :-)) a larger supply is a good thing, it gives you excess capacity for driving loads (for example if you wanted to attach a string of LEDs or some motors to your project). – dlu Dec 19 '15 at 16:20
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Make sure that the adapter you have is the correct polarity for the arduino or it won't work.

The barrel jack is centre positive, so look for this symbol on your adapter:

centre positive symbol

The barrel jack should have reverse voltage protection so it won't work if it's the wrong way around. The Vin pin doesn't have this protection, so be extra careful connecting things there.

  • If you're not sure and have a meter of some sort (or even an LED and a resistor where you know the polarity), check to confirm it. That said, it looks like the input is protected against reverse polarity (see the diode D1 in the upper right hand corner of the reference design). It looks like the board will not work if you have the polarity revised (the power LED should not come on). – dlu Dec 18 '15 at 19:33
  • Yep, you're right, sorry. The barrel jack does have reverse voltage protection, it's the Vin pin that doesn't have it. – MalphasWats Dec 18 '15 at 21:22
  • No problem. I had to look at at the schematic and it is way better to be safe than sorry :-) Good to add the point about the Vin pin, that's worth noting. – dlu Dec 18 '15 at 21:24
  • Polarity is not the issue..i just wanted to know if 2.5 amps of adapter will kill my board or not. – Awais Saifi Dec 19 '15 at 8:10

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