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From: Cursitor Doom <cd999666@notformail.com>
Newsgroups: sci.electronics.design
Subject: Re: MOSFET varieties
Date: Wed, 8 Jan 2025 23:55:06 -0000 (UTC)
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On Wed, 08 Jan 2025 10:18:47 -0800, john larkin wrote:

> On Wed, 8 Jan 2025 18:02:02 -0000 (UTC), Cursitor Doom
> <cd999666@notformail.com> wrote:
> 
>>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.
> 
> Ixys, now Littlefuse, makes a 4700 volt mosfet. It's about $100.

Wow! I am just so out of touch with what's available today. Fortunately, 
since I'm not a designer, I can afford to be. :)