zenseidk:
Hello,I have a DUE board and I want to power it with a 9V powersupply, which connects to a 5V regulator curcuit, which again connects through the Vin pin on the board. The board is built into a box and does now allow direct connection of the 9V powersupply.
Can I use 5V on the Vin pin or is that also a 3,3 V maximum?
VIN. The input voltage to the Arduino board when it's using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin, or if supplying voltage via the power jack, access it through this pin.
5V. This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.
As you see it's clear that you can supply your Due using 7-12 when using Vin.
http://arduino.cc/en/Main/arduinoBoardDue