What is a MOSFET, what does it look like, and how does it work?
MOSFETs come in four different types. They may be enhancement or depletion mode, and they may be n-channel or p-channel. For this application we are only interested in n-channel enhancement mode MOSFETs, and these will be the only ones talked about from now on. There are also logic-level MOSFETs and normal MOSFETs. The only difference between these is the voltage level required on the gate. Unlike bipolar transistors that are basically current-driven devices, MOSFETs are voltage-controlled power devices. If no positive voltage is applied between gate and source the MOSFET is always non-conducting. If we apply a positive voltage UGS to the gate we’ll set up an electrostatic field between it and the rest of the transistor. The positive gate voltage will push away the ‘holes’ inside the p-type substrate and attracts the moveable electrons in the n-type regions under the source and drain electrodes. This produces a layer just under the gate’s insulator through which electrons can get into
