I am working on a project with a Fez Cerb40 v1.1.
I need both 5V and 3.3V on this project.
My first prototype has 2 regulators, one for 5V and one for 3.3V, connected in series with an external 9V wall wart.
Runs fine with this setup.
However, I see that GHI now only sells v2 with added onboard regulator and cap, so I guess I will have to deal with that.
My project only uses USB for firmware update, and I want to let the possibility to the user to use a common regulated wall wart.
I guess I can keep one 5V regulator and connect this to VBUS on the Cerb 40 v2.
This will feed the internal regulator and it will work.
But what will happen when both wall wart and usb will be connected at the same time?
I read on this forum that this will work fine but I also know that paralleling voltage sources is not really something to do because voltages may be slightly different (and I think USB specs say that voltage might be between 4.75 - 5.25V, which is a rather huge tolerance).
Any opinion on this issue accepted