Re: MOSFET varieties

On Tue, 7 Jan 2025 23:57:23 -0000 (UTC), Phil Hobbs wrote:

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

That is truly impressive. I'll have to look the price up now, just out of
curiosity.