user15103: If an external voltage of 7 volts is applied to the external voltage input on the Arduino and the power from the USB port remains connected, is there a protective circuit that will protect the Arduino?  Thank you.

user20645: yes there is. power will be drained from external source(altough 7 volts is around the limit and arduino may switch to usb power) and arduino will still operate at 5v, same as usb. in any case your arduino and usb will be safe.

15103: <p>If an external voltage of 7 volts is applied to the external voltage input on the Arduino and the power from the USB port remains connected, is there a protective circuit that will protect the Arduino?  Thank you.</p>
 20645: <p>yes there is. power will be drained from external source(altough 7 volts is around the limit and arduino may switch to usb power) and arduino will still operate at 5v, same as usb. in any case your arduino and usb will be safe.</p>
