I'd like to use an Arduino Uno R3 battery powered a datalogger. I want do supply it directly with a Step-Up regulated 5Vv rechargable battery powersource at power pin 5V.

I don't want to suppy it with 5V at the PowerJack or Vin because it's not necessary an would result in lower voltage when powered with 5V at Vin and unnecessary power dissipation at U1.

Let's take a look at the schematic: http://arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf

I've edited it, take a look at the green areas and blue paths (ignore the yellow area at first): https://sharegallery.strato.com/pages/only-to-1st-post-at-se#electronics/photo/1962541 (Unfortunately first users are not allowed to post images with reputation < 10, I'll inline the image as soon as you give me enough upvotes=reputation :)

Just supplying it at that pin 5V however might destroy the linear regulator U1 that regulates >5V+ Vin down to 5V, I fear.

Question

• Is it acceptable and safe to suppy regulated 5V+ to pin 5V?
• Should I additionally short it to Vin ()?

Unfortunately there's no internal schematic for U1 (NCP1117ST50T3G) at AgeTeaTeaPea (unfortunately first users ...)://pdf1.alldatasheet.net/datasheet-pdf/view/174874/ONSEMI/NCP1117ST50T3G.html

For interest

Take a look at the yellow area: am I wrong or is the protection diode reversed? Shouldn't it have the catode at USBVcc?