stupid adaptor question

so I read that an ac/dc adaptor should be 9 to 12 volts. I found a way to power the arduino using the USB cable by using the plug from the kindle charger. it is rated at 4.9V and 0.85 amps. I know that it is a 5 volt system, so can I run it this way using this cable. In other words, am I hurting my board by using the USB but connected to the wall adaptor from the kindle?


No, that's basically the same as powering from your computer...

Awesome, thanks! That was kind of what I thought, but wanted to be sure so I didn't mess up my board. It was a convenient discovery. I had left my adaptor somewhere else and needed to power a small computer fan stirplate. Luckily the kindle adaptor worked.

The 9-12 range is for when you are feeding power to the five volt regulator through the power jack or the "Vin" pin. The regulator needs something like 7.5V minimum to regulate down to 5V. The USB power input is assumed to be regulated 5V and doesn't go through the regulator. If you have a regulated 5V supply you can connect it to the +5V pin which, like USB power, bypasses the regulator.