What is the simplest explanation of what a MOSFET is and does?
A mosfet is a type of transistor controlled by a gate voltage.
there are two applications of a mosfet. if it is used as a switch, if the source-to-source voltage exceeds the threshold voltage of the gate, the switch is activated, otherwise it is disabled. The other application of a mosfet is that of a voltage controlled current source. if the gate-to-gate voltage exceeds the threshold voltage and the source drain voltage is sufficiently positive, the source-to-source drain current will be proportional to the source gate voltage.
differs from a transistor, where a small current in the base controls a larger current from the collector to the emitter. a mosfet acts rather like a vacuum tube. it uses a voltage applied to the base to control the current through the device, from the drain to the source. a mosfet very much resembles a fetus in this respect.
finally, mosfets are much cheaper for high-current switching. when used as a simple switch, no heat sink is usually required.
For simplicity, ignore the first five letters. t represents the transistor. it is an electrical component that controls the flow of current, like a dimmer on the chandelier of your dining room.
by applying a voltage on the gate terminal, the current flows from the source terminal to the drain terminal. that’s what transistors do. more tension at the door, more flow. no voltage, no flow.
the most recent part refers to the type of transistor and its characteristics, you can read it on wikipedia.
a mosfet is like an aspiring dam! Water flowing through the turbines of the vacuum dam can feed a whole city of tens of thousands of houses and apartment buildings with hundreds of thousands of inhabitants. If you’ve ever visited a science museum and cycled with a dynamo, you know it takes a huge job just to power a 60-watt light bulb. you must pedal fully so that the bulb stays on.
What does my configuration have to do with your question?
imagine going to the dam of the vacuum cleaner. there is no water flowing through the turbines. your task is to turn on the power for the whole city. can you do it? Remember, you can not even generate enough power for a 60-watt light bulb.
… of course you can. simply turn the gate valves to allow massive flow of water to the turbines. you would have finished in less than an hour. you do not need to provide energy, you just have to release the massive energy from the dam water.
What does all this have to do with a mosfet?
the door of a mosfet lights the current from source to drain (do the rivers have springs and drains?). this current provides much more power than the small amount required to turn it on. it is the gain, the ability of a transistor to amplify a signal. the amplified signal can now power many more transistors.
A mosfet can control a large current with only a weak signal input.