I'm trying to understand MOSFETs, but I don't understand what I am seeing with my simple test circuit.
I have a FDP8440 logic level N-Channel MOSFET. Drain connected to 12V. Source connected to an LED, a resistor, and GND in series. I am switching the Gate between 12V and Ground to turn the MOSFET on/off. Trying to KISS, I'm leaving out the pull-up or pull-down resistor for now.
Why does my meter measure 12V at the Drain, but 10V at the Source? MOSFETs are "current controlled" and I have zero resistance between the 12V and the Gate. Is there not enough current in the load (LED) for it to make it up to 12V? Or, is there some sort of voltage drop associated with MOSFETs (like BJT?).
I'm confused...
Thanks for any words of wisdom.