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

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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 InstName R1
SYMATTR Value 100K
SYMBOL res 48 160 R0
SYMATTR InstName R2
SYMATTR Value 100K
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SYMATTR InstName R3
SYMATTR Value 100K
SYMBOL res 48 480 R0
SYMATTR InstName R4
SYMATTR Value 100K
SYMBOL res 256 144 R90
WINDOW 0 55 95 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 1E6
SYMBOL res 256 304 R90
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SYMATTR InstName R6
SYMATTR Value 1E6
SYMBOL res 256 464 R90
WINDOW 0 59 103 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 1E6
SYMBOL nmos 272 16 R0
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
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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 -388 186 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName I1
SYMATTR Value PWL(0 0 1E-3 0 1.001E-3 1 2E-3 1 2.001E-3 0.1 3E-3 0.1
3.001E-3 10 4E-3 10 4.001E-3 0)
SYMBOL voltage 560 512 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value 100
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SYMATTR Value 10n
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SYMATTR Value 10n
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SYMATTR Value 10n
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SYMATTR Value 10n
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SYMATTR Value 1K
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SYMATTR Value 1K
SYMBOL res -96 560 R0
SYMATTR InstName R11
SYMATTR Value 1K
TEXT -182 750 Left 2 !.tran 5E-3

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

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FLAG -112 160 VG3
FLAG -112 320 VG2
FLAG -112 480 VG1
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
SYMBOL res 256 144 R90
WINDOW 0 55 95 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 1E6
SYMBOL res 256 304 R90
WINDOW 0 57 103 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R6
SYMATTR Value 1E6
SYMBOL res 256 464 R90
WINDOW 0 59 103 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 1E6
SYMBOL nmos 272 16 R0
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
SYMATTR InstName V1
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
SYMBOL cap -96 496 R0
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

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

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!).