from Hacker News

FET: The Friendly Efficient Transistor

by l8rlump on 5/3/23, 10:34 AM with 21 comments

  • by Animats on 5/4/23, 5:13 AM

    That's a good explanation. Covers all the basics, including mentioning that FETs fail in the ON direction. This is why switching power supplies badly need protection circuitry, and why you don't want wall warts and battery chargers that didn't pass UL testing.

    He mentions electrostatic discharge sensitivity. Yes. It's very easy to blow out the gate of an FET just by touching the gate lead. Once it's attached to a driver transistor, it's protected, but loose FETs need to be stored in conductive foam and handled while wearing a wrist strap.

    FETs are really amazing. ON resistances in the milli-ohm range, and OFF resistances in the megohm range. It's surprising that's physically possible.

  • by cellularmitosis on 5/4/23, 5:59 AM

    > Speaking of the Pinecil, it uses an unorthodox driving circuit – it has an NPN transistor, but its base driven through a capacitor, so that only the AC component of the driving signal gets through. As a result, if the main MCU hangs and the control GPIO is stuck high, the FET won’t stay enabled!

    Clever!

  • by dvh on 5/4/23, 7:48 AM

    Jfets are used a lot in guitar pedals (j201, 2n5457, 2sk30a, ...). Unlike MOSFET they only need one gate resistor (10M gate to ground) in a input buffer configuration. The drain and source resistors are same as MOSFETs.

  • by l8rlump on 5/5/23, 7:07 AM

  • by adql on 5/4/23, 12:15 PM

    I'm annoyed that they just call MOSFETs FETs. There are different types dammit!