Re: MOSFET varieties

On Tue, 07 Jan 2025 11:24:56 -0800, john larkin 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.

Not sure I have *any* depletion mode FETs 'in stock' here. I have hundreds
of E-mode ones. Never ceases to amaze me how despite having tens of
thousands of parts, the design always seems to call for something I don't
have. Even if it's something - as in this case - that I designed myself!