Switching speed FETs §32.5

[@davidjmstewart]

After watching this video, I was disappointed to see you didn't have many videos on your channel. Your clarity and pacing is awesome.

[@gasstationwithoutpumps]

There are 40 hours of videos for my textbook. See the playlists at tinyurl.com/electronics-A and tinyurl.com/electronics-B

[@lohikarhu734]

good presentation...during my time at a certain mobile device manufacturer (13 years ago), developing DC/DC converters, switching speed was the double-edged sword, as you want fast switching, but EMC is a problem, and that "wasted" energy in total capacitance comes from precious run-time, i worked on driver ideas to get to the Miller plateau "instantly", then a controlled slew rate through that, and a terminated/controlled overvoltage for the on-time... you "only" need to know actual capacitance of the first two segments, and a "useful" Vgth + desired headroom...possible, then, to get very quickly to turn-on, have a desired slew rate of the switch, but with very little "extra" gate charge, and equally-fast turn-off... not something you do in discrete logic, but fairly do-able in a complex driver. cheers!

[@gasstationwithoutpumps]

Because my course was the second half of a first electronic course, I had to keep things fairly simple in this video, so I could not get into sophisticated driver design (even if I knew anything about the subject). Students doing the class-D amplifier lab do run into problems from too-slow or too-fast switching. THe problem they have is not so much from the electrical noise as from shoot-through current from not turning off the pFET as fast as the nFET turns on. Changing what pFET and nFET are used (as we did almost every year as cheap FETs reached end of life and became unavailable) or what voltage we operated at changed the tradeoffs, so students couldn't blindly copy designs.

[@magnuswootton6181]

so you can see here fets operate faster than 100 Mhz!!!

[@gasstationwithoutpumps]

Different FETs operate at different speeds-high-current ones tend to have very large gate charges (because of the large area of the gate to get sufficient channel width) and so are difficult to switch quickly-even getting over a MHz can be difficult. Tiny logic FETs, such as are used in modern processors, can switch at several GHz.