I have used commonly-available BJTs such as the 2N2222 and 2N3904 as switches by operating them in "saturation mode" from my MCU. I believe, however, that for these sorts of applications, a MOSFET is a more appropriate device. I have a few questions, however.
1) Does a MOSFET have a "saturation mode" like the BJT does? Is this "saturation" achieved by simply providing a high enough voltage on the base that the MOSFET is completely "on"?
2) Is it safe to drive the MOSFET directly from the MCU? I understand that the gate of the MOSFET behaves like a capacitor, and therefore draws some current while "charging", and then none thereafter. Is this charging current high enough to damage the MCU pin? By placing a resistor in series with the gate, I can protect the pin, but this will slow down the switch, possibly resulting in high heat dissipation by the MOSFET?
3) What is a common "hobbyist" MOSFET suitable for various low-power situation? I.E., what's the MOSFET equivalent to a 2N2222 or 2N3904?