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I have located the 5V voltage regulator chip on my Arduino board which I am hoping to use to power an attached device (which draws up to 500 mA at 5V). The chip is next to the plug for the external voltage supply. It says: ON RUX 117-5. It looks like it's in a SOT−223 package (body about 6.1 by 3.4mm).

I used this page to shows 3 different possible voltage regulators from ON Semiconductors: https://www.mouser.co.uk/ON-Semiconductor/Semiconductors/Power-Management-ICs/Voltage-Regulators-Voltage-Controllers/LDO-Voltage-Regulators/_/N-5cgac?P=1z0wa29Z1z0xwtvZ1z0zlrjZ1ywvc7yZ1yxz1yoZ1ywvc5z

This gives two unique data sheets for NCP1117LP and NCP1117, NCV1117. But this is where I'm stuck. They look pretty similar but not exactly the same data sheets. Also I don't know what RUX stands for, perhaps this is important in figuring out what power rating the Arduino 5V line has. Additionally the mouser.co.uk site says they're in SOT-223-3 packages but then gives dimensions which a) aren't the dimensions of the chip I have and b) are the dimensions of the SOT-223-4 package (6.3mm wide instead of the ~6.1 mm I have).

I don't care about the dimensions but I would like to correctly identify the chip on the Arduino board to be able to know what power I can draw from it before it shuts itself down.

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    The Arduno UNO SMD R2 uses an MCP33269 not an LM1117.What you have is probably some cheap Chinese clone of the Arduino, and in that case the regulator will be the cheapest Chinese copy of the LM1117 available. Impossible to tell what the specs of that specific chip are.Suffice it to say, though, that the specs of the chip are pretty much irrelevant since they rely on good heatsinking, which you most certainly don't have on a little Arduino board.500mA though is a lot to push through a linear regulator like that (depending of course on your unspecified input voltage which is a critical factor). – Majenko Jun 13 at 9:32
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    Better to get a proper switching regulator that can cope with the current without melting. – Majenko Jun 13 at 9:34
  • Thank you very much @Majenko . It makes sense now that this is a clone (I got it from a friend who would have just ordered it from the cheapest place)... that's what was tripping me up. Input voltage is 4 x 1.5V AA so ~6V. I will get a proper step down converter. Please add as an answer if you wish. – AJP Jun 13 at 9:49
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    If you're running from batteries then you definitely want the added efficiency of a switching regulator. – Majenko Jun 13 at 10:17
  • @Majenko, OP has in Question NCP1117 not LM1117. According to schematics orginal Uno R3 uses NCP1117ST50T3G – Juraj Jun 13 at 16:27
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The Arduno UNO SMD R2 uses an MCP33269 not an LM1117. What you have is probably some cheap Chinese clone of the Arduino, and in that case the regulator will be the cheapest Chinese copy of the LM1117 available. It's impossible to tell what the specs of that specific chip are. Suffice it to say, though, that the specs of the chip are pretty much irrelevant since they rely on good heatsinking, which you most certainly don't have on a little Arduino board.

500mA, though, is a lot to push through a linear regulator like that, and when running from batteries the excess power loss imposed by the regulator will be a major factor in longevity.

You are better off investing in a proper switching regulator (such as a UBEC from a model aircraft supplier like Hobbyking).

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