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From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>
Newsgroups: sci.electronics.design
Subject: Re: MOSFET varieties
Date: Tue, 7 Jan 2025 23:57:23 -0000 (UTC)
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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