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.