Why? Excuse my ignorance, I had my studies finished 30 years ago
Here are the advantages of MOSFETS:
(1) MOSFETs have an infinite power gain: you just place a voltage on the gate, of between 600mV to 12V, depending on the particular MOSFET, and the MOSFET can conduct up to around 50A, in practical terms. No current flows into the gate. Note that this is at DC. Because of the MOSFETs large effective input capacitance, you do need to provide more and more current to turn the MOSFET on and off fast. But once the MOSFET is on or off, no current, practically speaking, is required.
(2) When a MOSFET is turned on the MOSFET forms a a resistance between its drain and gate and the current can flow in either direction. Some MOSFETs can have a drain to source resistance as low as 3 mili Ohms. This relates to a forward drop of only, 3mR * 50A = 150mV. No other, reasonably priced, semiconductor device could match this.
(3) MOSFETs tend to have a better safe operating area (SOA), then bipolar junction transistors (BJTs). SOA indicates a devices ability to handle voltage and current at the same time.
(4) MOSFETs are incredibly fast compared to bipolar transistors, to a first approximation. But the parasitic capacitances of MOSFETS: Cds, Cdg, and Cgs, means that you need to use special circuits to realise the MOSFET's inherent speed. Cds can be especially significant, depending on the circuit configuration.
(5) MOSFETs have a huge parasitic diode from drain to source. The drain/source diode has similar voltage and current ratings to the MOSFET. The drain/source diode can be useful and other times it can be a nuisance. To block current in two direction a reverse blocking configuration is need where two similar MOSFETS are connected in reverse series.
(6) It is generally easier to connect MOSFETs in parallel to increase current handling.
(7) Because MOSFETs are so widely used, especially in switch mode power supplies (SMPs), they have the advantage of production scale, and are thus relatively cheap. This is in complete contrast to the situation up to around 1995.
(8) An unbelievably wide range of MOSFETs, to suit all applications, are available, from a large number of manufacturers.
Here is a link to the International Rectifier IRFPbF3206 which will give you a feel for a nice traditional high power NMOSFET:
https://www.infineon.com/dgdl/irfp3206pbf.pdf?fileId=5546d462533600a401535628d64a1ff0
There are also PMOSFET versions, but PMOSFEts tend to have double the Rdss.
More modern MOSFETs have lower gate drive voltage requirements.
The above covers medium and high power MOSFETs, but there is another general group: junction FETs (JFETs) and small signal MOSFETs.
These handle currents from 1mA to 500mA and are designed for high speed to extremely high speed operation. They have very low parasitic capacitances.
**broken link removed**
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