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I'm using a 12v fan and 12v LED modules in my project, so I need about 400mA by their combined specs. I have a 12.6v dc regulated power source that can give ~700mA I wish to use, and since it has a rather small form factor I would also like to power my Arduino Diecimila with it. I'm using PWM from pins 10 and 6 to go through N-channel MOSFETs in order to control both the LEDs and the fan. Anyway, in the Arduino Diecimila board page it says the recommended voltages are between 7-12v, and beyond that it can handle 6-20v, but it might cause the voltage regulator to heat too much, which might damage the board. So, my question is that: will 12.6v really damage my board, or is it within some margin of error? The actual voltage I got when I checked my power supply was 12.55V. Can I maybe just dial it down a bit somehow?

Thanks in advance,

UriSh.

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As you have already noticed, it may cause the 5V regulator to get hotter than would be normally considered reasonable. However, how hot depends entirely on how much current your board is drawing (not including the 12V devices)- the more current you draw the hotter it will get.

Even at 12V it can get uncomfortably hot.

For running off voltages greater than about 9V I usually recommend using an external 5V switching regulator. These can be easily and cheaply obtained under the name "UBEC" (Universal Battery Elimination Circuit) and are used extensively in the model aircraft arena. They don't get hot, can handle large currents, and don't waste power like the on-board linear regulator does.

So you'd connect that to your 12.6V supply, then the 5V output of the UBEC (make sure you get a 5V one) would go straight to the 5V pin of the Arduino, and you wouldn't connect the barrel jack or Vin to anything.

You can also pick up cheap switching regulators on eBay - some are adjustable, so you'd want to make sure you adjust it to 5V first before connecting the Arduino, or if you can adjust it to around 7V then you could power the Arduino through the barrel jack (or Vin) with it and avoid too much heat from the on-board linear regulator.

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