I'm working on a fairly complicated project and in the process I encountered a fairly simple problem. My project has a microcontroller which will, of course require programming. However, the PCB will draw its power from a custom designed motherboard, and for the purpose of testing and writing the firmware, it would be grossly inconvenient to require that it be connected to the motherboard simply to program it.
My solution was to simply stick a header onto the 5 V rail and power it externally. However, the 5 V rail is supplied by a linear regulator (LDL1117), which bucks 6 V from the mobo down to 5 V. This means that if I power the rail externally, the regulator will have 5 V at the output, while the input would be floating. Is this inherently a problem? Could this damage the regulator?