• mosfet strings

    From John Larkin@21:1/5 to All on Wed Apr 20 10:09:53 2022
    https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.

    --

    If a man will begin with certainties, he shall end with doubts,
    but if he will be content to begin with doubts he shall end in certainties. Francis Bacon

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Jan Panteltje@21:1/5 to jlarkin@highland_atwork_technology. on Wed Apr 20 17:41:17 2022
    On a sunny day (Wed, 20 Apr 2022 10:09:53 -0700) it happened John Larkin <jlarkin@highland_atwork_technology.com> wrote in <26f06hdar70hcvasi9l7m29agpafd9ui1o@4ax.com>:

    https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.

    Just wondering
    is it not simpler to use them all in parallel and connect the drains directly to the metal of the heatsink?
    Washers decrease thermal resistance

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Jan Panteltje@21:1/5 to pNaonStpealmtje@yahoo.com on Wed Apr 20 17:45:21 2022
    On a sunny day (Wed, 20 Apr 2022 17:41:17 GMT) it happened Jan Panteltje <pNaonStpealmtje@yahoo.com> wrote in <t3pgoe$el$1@dont-email.me>:

    On a sunny day (Wed, 20 Apr 2022 10:09:53 -0700) it happened John Larkin ><jlarkin@highland_atwork_technology.com> wrote in ><26f06hdar70hcvasi9l7m29agpafd9ui1o@4ax.com>:

    https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.

    Just wondering
    is it not simpler to use them all in parallel and connect the drains directly to the metal of the heatsink?
    Washers decrease thermal resistance

    oops increase I mean,
    and then insulate the heatsink.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Klaus Kragelund@21:1/5 to John Larkin on Wed Apr 20 22:41:14 2022
    20.04.22 20:09, John Larkin wrote: >https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.

    MOSFET strings are prone to problems. Dynamic switching can be solved with adding capacitors in the divider string

    --
    Klaus

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From John Larkin@21:1/5 to klauskvik@hotmail.com on Wed Apr 20 13:51:50 2022
    On Wed, 20 Apr 2022 22:41:14 +0300, Klaus Kragelund
    <klauskvik@hotmail.com> wrote:

    20.04.22 20:09, John Larkin wrote: >>https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.

    MOSFET strings are prone to problems. Dynamic switching can be solved with adding capacitors in the divider string

    I just want to burn watts to test the thermals. I do want the
    dissipations to be about equal among the fets.

    --

    If a man will begin with certainties, he shall end with doubts,
    but if he will be content to begin with doubts he shall end in certainties. Francis Bacon

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Martin Rid@21:1/5 to John Larkin on Wed Apr 20 17:19:58 2022
    John Larkin <jlarkin@highland_atwork_technology.com> Wrote in message:r
    https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1This is to test four fets on a heat sink for power dissipation.-- If a man will begin with certainties, he shall end with doubts, but if he will be content to begin with doubts he shall end
    in certainties.Francis Bacon

    I've seen the zener version used in a HV power supply about 20
    years ago.

    Cheers
    --


    ----Android NewsGroup Reader---- https://piaohong.s3-us-west-2.amazonaws.com/usenet/index.html

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From John Larkin@21:1/5 to klauskvik@hotmail.com on Wed Apr 20 16:43:37 2022
    On Wed, 20 Apr 2022 22:41:14 +0300, Klaus Kragelund
    <klauskvik@hotmail.com> wrote:

    20.04.22 20:09, John Larkin wrote: >>https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.

    MOSFET strings are prone to problems. Dynamic switching can be solved with adding capacitors in the divider string

    In this case, I just want the fets to get hot, to test a heat sink.

    --

    If a man will begin with certainties, he shall end with doubts,
    but if he will be content to begin with doubts he shall end in certainties. Francis Bacon

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Jan Panteltje@21:1/5 to jlarkin@highland_atwork_technology. on Thu Apr 21 05:28:27 2022
    On a sunny day (Wed, 20 Apr 2022 13:51:50 -0700) it happened John Larkin <jlarkin@highland_atwork_technology.com> wrote in <hhs06hpq06r1a50v8k6vknva5l34bp6vf0@4ax.com>:

    On Wed, 20 Apr 2022 22:41:14 +0300, Klaus Kragelund
    <klauskvik@hotmail.com> wrote:

    20.04.22 20:09, John Larkin wrote: >>>https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.

    MOSFET strings are prone to problems. Dynamic switching can be solved with adding capacitors in the divider string

    I just want to burn watts to test the thermals. I do want the
    dissipations to be about equal among the fets.

    Use power resistirs?
    Much simpler.
    http://panteltje.com/pub/power_resistors_IMG_6291.JPG

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From jlarkin@highlandsniptechnology.com@21:1/5 to pNaonStpealmtje@yahoo.com on Thu Apr 21 07:01:19 2022
    On Thu, 21 Apr 2022 05:28:27 GMT, Jan Panteltje
    <pNaonStpealmtje@yahoo.com> wrote:

    On a sunny day (Wed, 20 Apr 2022 13:51:50 -0700) it happened John Larkin ><jlarkin@highland_atwork_technology.com> wrote in ><hhs06hpq06r1a50v8k6vknva5l34bp6vf0@4ax.com>:

    On Wed, 20 Apr 2022 22:41:14 +0300, Klaus Kragelund
    <klauskvik@hotmail.com> wrote:

    20.04.22 20:09, John Larkin wrote: >>>>https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.

    MOSFET strings are prone to problems. Dynamic switching can be solved with adding capacitors in the divider string

    I just want to burn watts to test the thermals. I do want the
    dissipations to be about equal among the fets.

    Use power resistirs?
    Much simpler.
    http://panteltje.com/pub/power_resistors_IMG_6291.JPG


    The question is, how hot do these fets get on this heat sink?

    One issue with heat sinks is that the theta is usually/probably
    measured with heat uniformly applied to the baseplate. Real parts
    don't do that... they are usually a small number of hot spots. So
    footprints matter.

    My tests will use the real fets and the real insulators and we'll
    measure real fet temperatures.




    --

    I yam what I yam - Popeye

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Jan Panteltje@21:1/5 to jlarkin@highlandsniptechnology.com on Thu Apr 21 14:44:59 2022
    On a sunny day (Thu, 21 Apr 2022 07:01:19 -0700) it happened jlarkin@highlandsniptechnology.com wrote in <ilo26hlaqq7e711j4klot7ekc9oc5dgsng@4ax.com>:

    On Thu, 21 Apr 2022 05:28:27 GMT, Jan Panteltje
    <pNaonStpealmtje@yahoo.com> wrote:

    On a sunny day (Wed, 20 Apr 2022 13:51:50 -0700) it happened John Larkin >><jlarkin@highland_atwork_technology.com> wrote in >><hhs06hpq06r1a50v8k6vknva5l34bp6vf0@4ax.com>:

    On Wed, 20 Apr 2022 22:41:14 +0300, Klaus Kragelund >>><klauskvik@hotmail.com> wrote:

    20.04.22 20:09, John Larkin wrote: >>>>>https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.

    MOSFET strings are prone to problems. Dynamic switching can be solved with adding capacitors in the divider string

    I just want to burn watts to test the thermals. I do want the >>>dissipations to be about equal among the fets.

    Use power resistirs?
    Much simpler.
    http://panteltje.com/pub/power_resistors_IMG_6291.JPG


    The question is, how hot do these fets get on this heat sink?

    One issue with heat sinks is that the theta is usually/probably
    measured with heat uniformly applied to the baseplate. Real parts
    don't do that... they are usually a small number of hot spots. So
    footprints matter.

    My tests will use the real fets and the real insulators and we'll
    measure real fet temperatures.

    OK, if that is what you want to do,
    looks like a nice application for my FLIR camera recording.
    http://panteltje.com/panteltje/newsflex/download.html#xflir

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From jlarkin@highlandsniptechnology.com@21:1/5 to pNaonStpealmtje@yahoo.com on Thu Apr 21 08:16:01 2022
    On Thu, 21 Apr 2022 14:44:59 GMT, Jan Panteltje
    <pNaonStpealmtje@yahoo.com> wrote:

    On a sunny day (Thu, 21 Apr 2022 07:01:19 -0700) it happened >jlarkin@highlandsniptechnology.com wrote in ><ilo26hlaqq7e711j4klot7ekc9oc5dgsng@4ax.com>:

    On Thu, 21 Apr 2022 05:28:27 GMT, Jan Panteltje
    <pNaonStpealmtje@yahoo.com> wrote:

    On a sunny day (Wed, 20 Apr 2022 13:51:50 -0700) it happened John Larkin >>><jlarkin@highland_atwork_technology.com> wrote in >>><hhs06hpq06r1a50v8k6vknva5l34bp6vf0@4ax.com>:

    On Wed, 20 Apr 2022 22:41:14 +0300, Klaus Kragelund >>>><klauskvik@hotmail.com> wrote:

    20.04.22 20:09, John Larkin wrote: >>>>>>https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.

    MOSFET strings are prone to problems. Dynamic switching can be solved with adding capacitors in the divider string

    I just want to burn watts to test the thermals. I do want the >>>>dissipations to be about equal among the fets.

    Use power resistirs?
    Much simpler.
    http://panteltje.com/pub/power_resistors_IMG_6291.JPG


    The question is, how hot do these fets get on this heat sink?

    One issue with heat sinks is that the theta is usually/probably
    measured with heat uniformly applied to the baseplate. Real parts
    don't do that... they are usually a small number of hot spots. So >>footprints matter.

    My tests will use the real fets and the real insulators and we'll
    measure real fet temperatures.

    OK, if that is what you want to do,
    looks like a nice application for my FLIR camera recording.
    http://panteltje.com/panteltje/newsflex/download.html#xflir

    We have a big old E45 Flir with the gorgeous wide-angle germanium
    lens. That should be pretty good for snooping the tops of the mosfets
    and estimating junction temp.

    https://www.dropbox.com/s/bz6ueadispq6ril/CPU_Cooler_Washers.jpg?raw=1

    The option is to squash some of the thin foil thermocouples between
    the neoprene washer and the tops of the fets.

    We don't need extreme temp accuracy because the maximum power
    dissipation spec, and the max allowable Tj, will be mostly guesses.



    --

    I yam what I yam - Popeye

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From legg@21:1/5 to jlarkin@highland_atwork_technology. on Thu Apr 21 13:34:04 2022
    On Wed, 20 Apr 2022 10:09:53 -0700, John Larkin <jlarkin@highland_atwork_technology.com> wrote:

    https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.

    There has to be one element in the string to determine the
    string's function, before they can share the voltage stress.

    Rgs >> Rdiv and should not be in series with the divider
    string.

    Zeners can only zener. connecting drain to gate just gets a
    zener at Vgson.

    RL

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From John Larkin@21:1/5 to legg on Thu Apr 21 12:00:14 2022
    On Thu, 21 Apr 2022 13:34:04 -0400, legg <legg@nospam.magma.ca> wrote:

    On Wed, 20 Apr 2022 10:09:53 -0700, John Larkin ><jlarkin@highland_atwork_technology.com> wrote:

    https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.

    There has to be one element in the string to determine the
    string's function, before they can share the voltage stress.

    Rgs >> Rdiv and should not be in series with the divider
    string.

    Zeners can only zener. connecting drain to gate just gets a
    zener at Vgson.

    RL


    We will power the string from a big bench power supply, and we can set
    its voltage and current limit to get whatever power dissipation we
    want. We'd like the power per fet to be about the same, namely
    identical Vds, but we can measure the drop across each fet and
    calculate its actual dissipation.

    I wish we had software tools to simulate thermal situations like this,
    but lacking that we measure.

    --

    If a man will begin with certainties, he shall end with doubts,
    but if he will be content to begin with doubts he shall end in certainties. Francis Bacon

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Lasse Langwadt Christensen@21:1/5 to All on Thu Apr 21 12:53:45 2022
    onsdag den 20. april 2022 kl. 19.10.06 UTC+2 skrev John Larkin:
    https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.


    run them in reverse (using the body diode) from a current limited supply ?

    you might even be able to periodically get the actual die temperature,
    applying a small current and looking at the voltage drop

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From John Larkin@21:1/5 to langwadt@fonz.dk on Thu Apr 21 15:43:19 2022
    On Thu, 21 Apr 2022 12:53:45 -0700 (PDT), Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:

    onsdag den 20. april 2022 kl. 19.10.06 UTC+2 skrev John Larkin:
    https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.


    run them in reverse (using the body diode) from a current limited supply ?

    I want about 200 watts, but I guess as long as I can get some good
    thermal coefficients, I can scale.

    My "A" circuit would drop about 5 volts per fet at 10 amps, about 50
    watts per fet, which ain't bad. Those high voltage fets, IRFPS37N50A,
    need a lot of gate drive. Since I need to jump the gates to the
    drains, a resistor wouldn't be a bad way to do it, to keep the string
    from oscillating.


    you might even be able to periodically get the actual die temperature, >applying a small current and looking at the voltage drop

    That's a cute trick, but a lot of work. I can use a FLIR or
    thermocouples to look at the top of the fet package, which should
    work. The silicon slab is huge.

    The pulsed junction temperature trick needs a fast sampling voltage measurement. The old Tek differential comparator plugins like the type
    W or Z or 7A13 were great for this. There's nothing like that around
    any more, although a good digital scope should work.

    --

    If a man will begin with certainties, he shall end with doubts,
    but if he will be content to begin with doubts he shall end in certainties. Francis Bacon

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Lasse Langwadt Christensen@21:1/5 to All on Thu Apr 21 16:14:09 2022
    fredag den 22. april 2022 kl. 00.43.31 UTC+2 skrev John Larkin:
    On Thu, 21 Apr 2022 12:53:45 -0700 (PDT), Lasse Langwadt Christensen <lang...@fonz.dk> wrote:

    onsdag den 20. april 2022 kl. 19.10.06 UTC+2 skrev John Larkin:
    https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.


    run them in reverse (using the body diode) from a current limited supply ?
    I want about 200 watts, but I guess as long as I can get some good
    thermal coefficients, I can scale.

    My "A" circuit would drop about 5 volts per fet at 10 amps, about 50
    watts per fet, which ain't bad. Those high voltage fets, IRFPS37N50A,
    need a lot of gate drive. Since I need to jump the gates to the
    drains, a resistor wouldn't be a bad way to do it, to keep the string
    from oscillating.

    you might even be able to periodically get the actual die temperature, >applying a small current and looking at the voltage drop
    That's a cute trick, but a lot of work. I can use a FLIR or
    thermocouples to look at the top of the fet package, which should
    work. The silicon slab is huge.

    The pulsed junction temperature trick needs a fast sampling voltage measurement. The old Tek differential comparator plugins like the type
    W or Z or 7A13 were great for this. There's nothing like that around
    any more, although a good digital scope should work.
    --

    I imagine something like a resistor in series with a CC/CV supply
    CV and resistor set measurement current, short the resistor CC sets the power level
    scope or multimeter across the mosfet stack measure voltage drop
    calibrating at two known temperatures will probably do

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From legg@21:1/5 to jlarkin@highland_atwork_technology. on Fri Apr 22 17:11:59 2022
    On Thu, 21 Apr 2022 12:00:14 -0700, John Larkin <jlarkin@highland_atwork_technology.com> wrote:

    On Thu, 21 Apr 2022 13:34:04 -0400, legg <legg@nospam.magma.ca> wrote:

    On Wed, 20 Apr 2022 10:09:53 -0700, John Larkin >><jlarkin@highland_atwork_technology.com> wrote:

    https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.

    There has to be one element in the string to determine the
    string's function, before they can share the voltage stress.

    Rgs >> Rdiv and should not be in series with the divider
    string.

    Zeners can only zener. connecting drain to gate just gets a
    zener at Vgson.

    RL


    We will power the string from a big bench power supply, and we can set
    its voltage and current limit to get whatever power dissipation we
    want. We'd like the power per fet to be about the same, namely
    identical Vds, but we can measure the drop across each fet and
    calculate its actual dissipation.

    I wish we had software tools to simulate thermal situations like this,
    but lacking that we measure.

    watch for text wrap on PWL

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    SYMATTR Value 1K
    TEXT -182 750 Left 2 !.tran 5E-3

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From legg@21:1/5 to jlarkin@highland_atwork_technology. on Fri Apr 22 17:17:15 2022
    On Thu, 21 Apr 2022 12:00:14 -0700, John Larkin <jlarkin@highland_atwork_technology.com> wrote:

    On Thu, 21 Apr 2022 13:34:04 -0400, legg <legg@nospam.magma.ca> wrote:

    On Wed, 20 Apr 2022 10:09:53 -0700, John Larkin >><jlarkin@highland_atwork_technology.com> wrote:

    https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.

    There has to be one element in the string to determine the
    string's function, before they can share the voltage stress.

    Rgs >> Rdiv and should not be in series with the divider
    string.

    Zeners can only zener. connecting drain to gate just gets a
    zener at Vgson.

    RL


    We will power the string from a big bench power supply, and we can set
    its voltage and current limit to get whatever power dissipation we
    want. We'd like the power per fet to be about the same, namely
    identical Vds, but we can measure the drop across each fet and
    calculate its actual dissipation.

    I wish we had software tools to simulate thermal situations like this,
    but lacking that we measure.

    Check out the voltage compliance of the control element for constant
    current

    Version 4
    SHEET 1 1784 768
    WIRE 64 -16 -80 -16
    WIRE 320 -16 64 -16
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    WIRE -80 64 -80 48
    WIRE 272 96 112 96
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    WIRE 176 112 112 112
    WIRE 288 112 240 112
    WIRE -80 160 -80 144
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    WIRE 64 176 64 160
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    WIRE 352 320 320 320
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    WIRE -80 400 -80 384
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    WIRE -80 496 -80 480
    WIRE 64 496 64 480
    WIRE 560 528 560 -16
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    FLAG 560 704 0
    SYMBOL res 48 0 R0
    SYMATTR InstName R1
    SYMATTR Value 100K
    SYMBOL res 48 160 R0
    SYMATTR InstName R2
    SYMATTR Value 100K
    SYMBOL res 48 304 R0
    SYMATTR InstName R3
    SYMATTR Value 100K
    SYMBOL res 48 480 R0
    SYMATTR InstName R4
    SYMATTR Value 100K
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    WINDOW 0 55 95 VBottom 2
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    SYMATTR Value 1E6
    SYMBOL res 256 304 R90
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    SYMATTR Value 1E6
    SYMBOL res 256 464 R90
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    SYMATTR Value 1E6
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    SYMATTR InstName M1
    SYMATTR Value BSC340N08NS3
    SYMBOL nmos 272 176 R0
    SYMATTR InstName M2
    SYMATTR Value BSC340N08NS3
    SYMBOL nmos 272 336 R0
    SYMATTR InstName M3
    SYMATTR Value BSC340N08NS3
    SYMBOL zener 240 96 R90
    WINDOW 0 0 32 VBottom 2
    WINDOW 3 32 32 VTop 2
    SYMATTR InstName D1
    SYMATTR Value BZX84C6V2L
    SYMATTR Description Diode
    SYMATTR Type diode
    SYMBOL zener 240 256 R90
    WINDOW 0 0 32 VBottom 2
    WINDOW 3 32 32 VTop 2
    SYMATTR InstName D2
    SYMATTR Value BZX84C6V2L
    SYMATTR Description Diode
    SYMATTR Type diode
    SYMBOL zener 240 416 R90
    WINDOW 0 0 32 VBottom 2
    WINDOW 3 32 32 VTop 2
    SYMATTR InstName D3
    SYMATTR Value BZX84C6V2L
    SYMATTR Description Diode
    SYMATTR Type diode
    SYMBOL current 320 544 R0
    WINDOW 3 29 80 Left 2
    WINDOW 123 0 0 Left 2
    WINDOW 39 0 0 Left 2
    SYMATTR InstName I1
    SYMATTR Value 1
    SYMBOL voltage 560 512 R0
    WINDOW 123 0 0 Left 2
    WINDOW 39 0 0 Left 2
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    SYMATTR Value PWL(0 10 1E-3 10 1.001E-3 100 2E-3 100 2.001E-3 40 3E-3
    40 3.001E-3 140 4E-3 140 4.001E-3 0)
    SYMBOL cap -96 -16 R0
    SYMATTR InstName C1
    SYMATTR Value 10n
    SYMBOL cap -96 160 R0
    SYMATTR InstName C2
    SYMATTR Value 10n
    SYMBOL cap -96 320 R0
    SYMATTR InstName C3
    SYMATTR Value 10n
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    SYMATTR InstName C4
    SYMATTR Value 10n
    SYMBOL res -96 48 R0
    SYMATTR InstName R8
    SYMATTR Value 1K
    SYMBOL res -96 224 R0
    SYMATTR InstName R9
    SYMATTR Value 1K
    SYMBOL res -96 384 R0
    SYMATTR InstName R10
    SYMATTR Value 1K
    SYMBOL res -96 560 R0
    SYMATTR InstName R11
    SYMATTR Value 1K
    TEXT -182 750 Left 2 !.tran 5E-3

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From jlarkin@highlandsniptechnology.com@21:1/5 to legg on Fri Apr 22 19:52:29 2022
    On Fri, 22 Apr 2022 17:17:15 -0400, legg <legg@nospam.magma.ca> wrote:

    On Thu, 21 Apr 2022 12:00:14 -0700, John Larkin ><jlarkin@highland_atwork_technology.com> wrote:

    On Thu, 21 Apr 2022 13:34:04 -0400, legg <legg@nospam.magma.ca> wrote:

    On Wed, 20 Apr 2022 10:09:53 -0700, John Larkin >>><jlarkin@highland_atwork_technology.com> wrote:

    https://www.dropbox.com/s/s6nfu30ldyzvpqy/Fet_String.jpg?raw=1

    This is to test four fets on a heat sink for power dissipation.

    There has to be one element in the string to determine the
    string's function, before they can share the voltage stress.

    Rgs >> Rdiv and should not be in series with the divider
    string.

    Zeners can only zener. connecting drain to gate just gets a
    zener at Vgson.

    RL


    We will power the string from a big bench power supply, and we can set
    its voltage and current limit to get whatever power dissipation we
    want. We'd like the power per fet to be about the same, namely
    identical Vds, but we can measure the drop across each fet and
    calculate its actual dissipation.

    I wish we had software tools to simulate thermal situations like this,
    but lacking that we measure.

    Check out the voltage compliance of the control element for constant
    current

    I was recently scribbling something similar for a high voltage power
    supply, namely a stack of fets. In my case, your I1 becomes my
    optocoupler. M3 could be a depletion fet.



    --

    I yam what I yam - Popeye

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Jan Panteltje@21:1/5 to jlarkin@highlandsniptechnology.com on Sun Apr 24 05:58:15 2022
    On a sunny day (Thu, 21 Apr 2022 08:16:01 -0700) it happened jlarkin@highlandsniptechnology.com wrote in <vrs26h5si785ma2742kns05rvbpoa0optg@4ax.com>:

    On Thu, 21 Apr 2022 14:44:59 GMT, Jan Panteltje
    <pNaonStpealmtje@yahoo.com> wrote:
    looks like a nice application for my FLIR camera recording.
    http://panteltje.com/panteltje/newsflex/download.html#xflir

    We have a big old E45 Flir with the gorgeous wide-angle germanium
    lens. That should be pretty good for snooping the tops of the mosfets
    and estimating junction temp.

    The nice thing about being able to record temperature is
    that you can fast forward or slow motion it later in playback to see
    how heat spreads over time etc.
    should not be that hard to add current or voltage or some other parameter as subtitle.
    (idea!).

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