Which Arduino?
What do you mean by "then the 5v supply is providing ~40mA"
If you power the Arduino via the Vin that voltage needs to be at least 7V. You need the extra for the regulator drop and only that way the USB power is turned off.
Which Arduino?
What do you mean by "then the 5v supply is providing ~40mA"
If you power the Arduino via the Vin that voltage needs to be at least 7V. You need the extra for the regulator drop and only that way the USB power is turned off.