• Re: MOSFET varieties

    From Cursitor Doom@21:1/5 to Phil Hobbs on Tue Jan 7 16:11:48 2025
    On Tue, 7 Jan 2025 15:45:58 -0000 (UTC), Phil Hobbs wrote:

    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


    Reverse supply polarity and use a depletion NFET. (You’re basically
    asking for a depletion PFET, but nobody makes them. )

    Cheers

    Phil Hobbs

    Many thanks, Phil.

    --- SoupGate-Win32 v1.05
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  • From Phil Hobbs@21:1/5 to Cursitor Doom on Tue Jan 7 15:45:58 2025
    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


    Reverse supply polarity and use a depletion NFET. (You’re basically asking for a depletion PFET, but nobody makes them. )

    Cheers

    Phil Hobbs

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

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Cursitor Doom@21:1/5 to All on Tue Jan 7 15:19:08 2025
    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

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to cd999666@notformail.com on Tue Jan 7 08:22:37 2025
    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?

    Supertex is now a Microchip company.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Cursitor Doom@21:1/5 to john larkin on Tue Jan 7 18:59:33 2025
    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! :)

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to cd999666@notformail.com on Tue Jan 7 11:24:56 2025
    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.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Cursitor Doom@21:1/5 to john larkin on Tue Jan 7 22:34:04 2025
    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!

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Hobbs@21:1/5 to john larkin on Tue Jan 7 23:57:23 2025
    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

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to pcdhSpamMeSenseless@electrooptical. on Tue Jan 7 16:17:33 2025
    On Tue, 7 Jan 2025 23:57:23 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> 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

    I used some 1200 volt Cree SiC fets in my Pockels Cell driver. They
    are a niusance to drive, +18 and -12 on the gate. Had to use GaN fets
    to drive that.

    Silicon drives GaN drives SiC.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Cursitor Doom@21:1/5 to Phil Hobbs on Wed Jan 8 18:02:02 2025
    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.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From john larkin@21:1/5 to cd999666@notformail.com on Wed Jan 8 10:18:47 2025
    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.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Cursitor Doom@21:1/5 to john larkin on Wed Jan 8 23:55:06 2025
    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. :)

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)