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?