MOSFET is a commonly used type of transistor that is used for amplifying and/or switching electronic signals. It stands for ‘Metal Oxide Semiconductor Field Effect Transistor’. It has generally four terminals, which are, source (S), gate (G), drain (D) and body or substrate (B). But, body or substrate terminal is often internally connected to source (S) terminal, and thus, making it a three terminal device like other transistors.
Power MOSFET is specially designed type to handle larger power ratings. Basically, it is a voltage controlled device. Though, it is hard to explain the working principle without diagram (this forum is new and I’m yet to add support for images in these forums), working of a mosfet can be told at its most basic form as follows. Considering an n channel MOSFET, if a positive voltage is applied to the Gate (G) terminal with respect to the Source (S) terminal, the holes in the p type substrate are pushed away and at the same time electrons from the n+ type Source and Drain are attracted to form a channel just below the insulation layer (called as MOS capacitor) of the gate. Thus, an n type channel with movable electrons is formed between the Source and Drain. Thus, the cannel allows flow of current from drain to source. If the gate voltage is increased, width of the channel increases, and thus, allowing more amount of current. Hence, drain to source current can be controlled by controlling the Gate voltage.
Apologies again as the characteristics of a powet mosfet can not be explained without proper diagram. I’ll add the support for images in this forum asap!