most mobile phone power supply are 0.5-1.0A only, which is not enough under load (according to digilent).
This is what the manual says:Quote
Our out-of-box demo draws ~400mA of
current from the 5V input rail. A few demanding applications, including any that drive multiple peripheral boards,
might require more power than the USB port can provide. Also, some applications may need to run without being
connected to a PC’s USB port. In these instances, an external power supply or battery pack can be used.
An external power supply can be used by plugging into to the power jack (JP3) and setting jumper J13 to “wall”.
The supply must use a coax, center-positive 2.1mm internal-diameter plug, and deliver 4.5VDC to 5.5VDC and at
least 1A of current (i.e., at least 5W of power). Many suitable supplies can be purchased from Digilent, through
Digi-Key, or other catalog vendors.
I use a 3A coax psu, so I can´t really tell if a 1A usb psu (for example) works well...
iirc, Paul is using the PCs USB power to power the Nexys and never encountered problems.
I bought an external Power supply, just to be on the safe side.
I use an 5V/3A supply either. That works fine.
We use 5V/2A refurbished from Pollin. Around 3 Euros each, no problems so far
edit: That's for the pre-series machines, not the Nexys board. However, should be fine too!