I noticed that there are more N-channel mostfets than P-channel mosfets on the market.
Then I realised that probably in many applications, the high powered device runs on a higher voltage and therefore a P-channel mosfet cannot be used.
An N-channel mostfet connects the ground lines of the high-power device to ground. However this is not "common" ground. Its ground + the potential of the mosfet.
I actually have a lot of components (all 5V) to be controlled by one MOSFET switch including digital logic. I need this to isolate out that part of the board when my board is only being powered by PC USB. (ie: 500mA limited, and this part of the board draws 1.5A and should only work when on USB charger)
I was thinking of putting in a P-channel mosfet into my design so that my microcontroller is controlling the highrail of my high-powered device (a light, a motor, etc), rather than the ground rail. It feels like that would make sense because then one maintains a solid ground plane on the entire board. Perhaps this is not as important as I was lead to beleive in school?
Best Answer
I think we'd need to see the exact situation you're thinking about to give you a real answer, but in general,
getting the grounding scheme right can be VERY important, and
Sometimes getting the grounding scheme right can mean separating your grounds, or even isolating part of your circuit such that one part does not share a common ground with the rest of your circuit.