I'm designing a shield for the Arduino Uno with some sensors that require +5V, +3V3 and +3V Vdd. I want to power everything with a single DC adapter so I have a voltage regulator that converts the DC input (+12 - +26V DC) to 5V DC with a maximum current of 1A. That output goes into the 5V sensors, 3V3 and 3V regulators.
Since this is already regulated power can I connect the 5V 1A output to the +5V pin on the Arduino, bypassing the voltage regulator on the Arduino? Or is it better to have another +10V voltage regulator parallel to the 5V regulator that goes into the 9-12V Vin on the Arduino (that than goes to the 5V voltage regulator on the Arduino)?
If I do the first option, is it then save to have the USB connector plugged in?