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Author Topic: 12v Power supply for Uno, Smart idea?  (Read 1429 times)
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Is it smart to  use a 12vDC / 2A regulated power supply for an Arduino Uno?
I have heard that the voltage regulator on the Arduino may overheat.

My project is a 4 digit (seven segment display).
I am using a max7219,source driver and sink drivers to deliver the external 12v power supply to my display (Segments require 60ma/9V).

Therefore I beleive the arduino is only using 5v to power the max 7219 and small amps to open the source drive outputs. Everything is working GREAT right now. But I am finalizing the project and want to only have one power source to my project. I have been powering the Arduino by USB until this point. I do want to utilize the 12v/dc regulated power to power the Arduino.

I was wondering if I should regulate the 12v source to 7volts before plugging into Arduino?
Any thoughts?  I would hate to overheat my Arduino
(I am new to this and am proud of how much I have learned in 6 months.)
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Is it smart to  use a 12vDC / 2A regulated power supply for an Arduino Uno?
I have heard that the voltage regulator on the Arduino may overheat.

It depends on how much power is drawn through the regulator.

Therefore I beleive the arduino is only using 5v to power the max 7219 and small amps to open the source drive outputs. Everything is working GREAT right now. But I am finalizing the project and want to only have one power source to my project. I have been powering the Arduino by USB until this point. I do want to utilize the 12v/dc regulated power to power the Arduino.

If that's everything then you're only drawing about 50mA of current and you should be fine.

PS: A simple test is to put your finger on the regulator...if you say "ow!" then you need to reduce the load.

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if you say "ow!" then you need to reduce the load.

Or lower the input voltage. Higher input voltage = more voltage to drop = more heat.

BTW, 12V is listed as the upper recommended supply voltage in the Uno specs.

That is what is getting me a little nervous, (the 12v upper limit). That is why I thought about lowering input voltage with a regulator before it gets to Arduino and its regulator.
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The Arduino will not get broke with 12V.
The voltage regulator turns the current down if it gets too hot.

And yes, it is true. Put your finger on the voltage regulator. If you can't keep your finger on it, you might have to lower the voltage.
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Although, I just looked at my Uno R3 and it uses an NCP1117 regulator, which automatically shuts down if it gets too hot. According to the datasheet, that happens around 175°C.

Definitely going to make you say "ow!".

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Thank You all for your input.
It is nice to know the arduino will not get ruined.
I will test and see if it gets warm.
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You can connect your "4 digit (seven segment display)" directly to the 12V with correct serial resistors.

When you will light the segment you will "sink" the current. The "sinked" current is not provided by the arduino regulator but directly by the 12v power supply. This current flow out the chip only by ground wires.

The "heat" is function of the U*I product by decreasing the current you  minimize the "heat" of the régulator.

Due to my poor english an example is better :
4 digit *7 segment need 4*7*20mA = 560 mA
Regulator input =12V output = 5V,  drop out = 12 -0.8 -5 = 6.2 V (0.8V for the serial diode, see schematic).
current for the arduino board ~ 50 mA. (it is an estimation)

1) 4 digit *7 segment current furnish by arduino regulator :
Power (regulator) = 6.2 *(0,56+ 0,05) = 3.8 W

Thermal resistance of the regulateur case : 220 °C/W
Ambiant temperature : 30°C
Regulator Junction temperature = 30 + 220 * 3.8 = 866 °C  >120°C -> the regulator die.

2) 4 digit *7 segment current furnish by 12v power supply
Power  (regulator) = 6.2 *( 0,05) = 0.31 W
Regulator Junction temperature = 30 + 220 * 0.31 = 77.5 °C  < 120°C -> the regulator is alive
« Last Edit: March 01, 2013, 01:27:10 pm by 68tjs » Logged

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The tests I have done have shown that at 12V and room temperature, you can get about 400mA through the regulator on an Uno R3 which is using a SOT-223 package.

The older boards can do a little closer to 600mA.

Keep in mind these currents are when the regulator starts going into thermal shutdown, so it is being operated at its limit.  The external package will be at about 100C which will leave a nice mark on your finger if touched.
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Why build a heavy duty 12V supply when you can't draw all that current from it?  Why not a 2A 5V supply instead and feed it into the board after the onboard regulator?  Of course you'll have to be more careful since things that didn't kill the board before because of limiting by the onboard regulator will now kill it. 

If you really need the 12V output, then maybe a 12V and 7.5V dual output supply would be possible.  That would let you keep the safety of the onboard regulator and keep the dissipation down by not burning up the extra 4.5V with it. 

I think it would be nice to have a triple output supply generating 12V, 7.5V and 5V.  12V for motors and what-not, 7.5 to feed the Arduino thru it's normal PS connector, and 5V to put onto the breadboard rails instead of jumpering the Arduino supply pin to the rail.  This would take a real load off the Arduino.  You could even skip the 7.5V and feed 12V to it because it should never have reason to draw more than a few mA.  You would still need to connect the grounds of course.
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