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Author Topic: More than 12VDC to your Arduino Uno and someone is going to get hurt  (Read 1043 times)
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According to the Arduino Uno specifications, the recommended input voltage is 7-12V and the limits of that input voltage is 6-20V.
http://www.arduino.cc/en/Main/arduinoBoardUno

This would mean to someone that it is possible to apply up to 20 volts at the VIN node. But, is this healthy? Can the board to cope with more than 12V?
Let's look at this more closely:

The Onsemi 5V regulator U1 (NCP1117ST50T3G) is rated for a maximum input voltage of 20V, so supplying 20V will not damage the regulator. The 47uF input capacitor (PC1) is rated at 25V, so those 20V will not damage that component as well.

However, supplying a 20V will rise the VIN node.  This will affect the U5 (LMV358IDGKR) comparator input (CMP - +3V3).  When you supply a 20V at the input (PWRIN), the VIN node will drop down to 19V due to D1.   The 19V is then divided into half by RN1A and RN1B to 9.5V, which is 'almost' twice (5.5V+5.5V) the LMV358 maximum input rating. So, if we supply a 20V, the LMV358 will be killed. Because of this, we should not supply more than the recommended 7-12V. Am I right?

One solution is to replace one/both 10kohm resistors (RN1A - RN1B) and adjust their voltage divider network to lower the voltage at the CMP node. But for this, it is required to know how to solder and have access to SMD resistors.

Comments will be very welcome.
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SE USA
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you should not go above 12 volts because of heat

sure you could suck nearly an amp out of it with a 20 volt input, 15 volt drop, but you better have that joker welded (cause solder wont hold) to a brick of metal and a fan on it

even a TO220 package with a small heatsink is going to start to get a little spicy with only a few hundred mA load and a 12 volt input.
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why not check - http://ruggedcircuits.com/html/ruggeduino.html - probably the most robust duino in the world
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Rob Tillaart

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you should not go above 12 volts because of heat

sure you could suck nearly an amp out of it with a 20 volt input, 15 volt drop, but you better have that joker welded (cause solder wont hold) to a brick of metal and a fan on it

Well I suspect the regulator will just go into automatic self-protection mode and shutdown well before it tries to unsolder itself. But armageddon stories are so much more fun and it's also fun to scare the newbies.  smiley-wink

even a TO220 package with a small heatsink is going to start to get a little spicy with only a few hundred mA load and a 12 volt input.
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