Re: MOSFET varieties

john larkin <jl@glen--canyon.com> wrote:

On Tue, 7 Jan 2025 18:59:33 -0000 (UTC), Cursitor Doom
<cd999666@notformail.com> wrote:
 

On Tue, 07 Jan 2025 08:22:37 -0800, john larkin wrote:
 

On Tue, 7 Jan 2025 15:19:08 -0000 (UTC), Cursitor Doom
<cd999666@notformail.com> wrote:
 

Gentlemen,
 
Is there a type of MOSFET which is normally 'on' with zero or low
positive gate voltage wrt source, but turns 'off' when Vgs is increased
to a higher positive 'threshold' value?
 
CD

 
A p-channel JFET would do that.
 
Supertex makes some great depletion-mode NFETS, and someone else has
equivalents. They make nice constant-current loads and current limiters.
 
What are you trying to do?

 
Thanks, John, but I don't want to start another lengthy thread here which
would no doubt happen if I explained - and everyone chipping in a
different idea so I end up losing track. So - no comment! :)

 
Well, OK. I like to post problems here to brainstorm possibilities.
Even silly ideas help me think about possibilities.
 
But one can get lost-in-space too. Confusion is good, but not forever.
 
Depletion fets are great fun. I like to discharge power supply caps
with a depletion fet and an LED. It discharges linearly and winks out
at 2 or 3 volts.
 
 

BTW I discover that there are 1700V SiC JFETs, such as the Qorvo
UF3N170400B7S.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics