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What is the difference between source and drain?
From a circuit perspective, the “source” of an Nchannel MOSFET is the terminal at the LOWER voltage and the “drain” of an Nchannel MOSFET is the terminal at the HIGHER voltage.
Why source and drain are heavily doped?
The source/drain regions of a MOSFET (see figure 5 are, as a consequence, heavily doped to provide a good contact between the source/drain region on the semiconductor and the source/drain metallization (black areas in the image) and to avoid unwanted Schottky junctions.
Are source and drain interchangeable?
Theoretically, the drain and source can be swapped, and when you do this, the source becomes the drain and the drain becomes the source. For an N-MOSFET, the source is the lower potential, and the drain is the higher potential.
What is the symetry between drain and source in a MOSFET?
For a N channel mosfet the doping arrangements result in diodes that permit current flow from body to drain and from body to source. If you have a mosfet with all four terminals brought out seperately then there is a symetry between drain and source.
How is the gate lowered in a p channel MOSFET?
To turn it on, the gate is lowered by 12-15V with respect to the source for most normal MOSFETs. If you want a ground-referenced load, you can use a P channel MOSFET. This will be a mirror-image of the circuit you describe, ie with the source connected to the higher voltage and the drain connected to 0V via the load.
Can a MOSFET be a ground referenced load?
If you want a ground-referenced load, you can use a P channel MOSFET. This will be a mirror-image of the circuit you describe, ie with the source connected to the higher voltage and the drain connected to 0V via the load. However, your gate drive will need to be reversed and will need to be close to your higher voltage to turn the load off.
Where does the diode point in a MOSFET?
To clarify a bit what others have already said, a MOSFET has a internal diode that points from source to drain in N channel devices and drain to source in P channel devices. This is not something added deliberately by the manufacturer, but is a byproduct of the way MOSFETs are made.