OT: Power BJT Power Limit...

[Cursitor Doom]

Gentlemen,

Taking the 2N3055 as an example (as I\'m sure we\'re all familiar with
this once-ubiquitous decades-old device) say if you were to rig up
some apparatus which enabled you to flood its case with a stream of
say liquid helium, how much power could you wring out of it? I don\'t
mean theoretically, I mean *practically* taking into account its
real-world limitations. Any idea?

Thanks,

CD

 

[Phil Hobbs]

On 2020-07-26 12:50, Cursitor Doom wrote:

Gentlemen,

Taking the 2N3055 as an example (as I\'m sure we\'re all familiar with
this once-ubiquitous decades-old device) say if you were to rig up
some apparatus which enabled you to flood its case with a stream of
say liquid helium, how much power could you wring out of it? I don\'t
mean theoretically, I mean *practically* taking into account its
real-world limitations. Any idea?

Thanks,

CD

It would probably be limited by die cracking due to differential thermal
expansion at the high voltage end and bond wires blowing off at the high
current end.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Cursitor Doom]

hOn Sun, 26 Jul 2020 12:51:46 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

It would probably be limited by die cracking due to differential thermal
expansion at the high voltage end and bond wires blowing off at the high
current end.

Wow, Phil, you broke the speed of light with that reply!! :-D

 

[Phil Hobbs]

On 2020-07-26 12:55, Cursitor Doom wrote:

hOn Sun, 26 Jul 2020 12:51:46 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

It would probably be limited by die cracking due to differential
thermal expansion at the high voltage end and bond wires blowing
off at the high current end.

Wow, Phil, you broke the speed of light with that reply!! :-D

Bored, bored, bored.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[server]

On Sun, 26 Jul 2020 17:50:05 +0100, Cursitor Doom
<curd@notformail.com> wrote:

Gentlemen,

Taking the 2N3055 as an example (as I\'m sure we\'re all familiar with
this once-ubiquitous decades-old device) say if you were to rig up
some apparatus which enabled you to flood its case with a stream of
say liquid helium, how much power could you wring out of it? I don\'t
mean theoretically, I mean *practically* taking into account its
real-world limitations. Any idea?

Thanks,

CD

Bipolar transistors don\'t work at liquid helium temps! Better try
liquid nitrogen. Or cold water.





--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Phil Hobbs]

On 2020-07-26 14:06, jlarkin@highlandsniptechnology.com wrote:

On Sun, 26 Jul 2020 17:50:05 +0100, Cursitor Doom
curd@notformail.com> wrote:

Gentlemen,

Taking the 2N3055 as an example (as I\'m sure we\'re all familiar with
this once-ubiquitous decades-old device) say if you were to rig up
some apparatus which enabled you to flood its case with a stream of
say liquid helium, how much power could you wring out of it? I don\'t
mean theoretically, I mean *practically* taking into account its
real-world limitations. Any idea?

Thanks,

CD

Bipolar transistors don\'t work at liquid helium temps! Better try
liquid nitrogen. Or cold water.

You just have to turn the current on before the helium, and do the
measurement fast before you run out of money.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[bitrex]

On 7/26/2020 2:06 PM, jlarkin@highlandsniptechnology.com wrote:

On Sun, 26 Jul 2020 17:50:05 +0100, Cursitor Doom
curd@notformail.com> wrote:

Gentlemen,

Taking the 2N3055 as an example (as I\'m sure we\'re all familiar with
this once-ubiquitous decades-old device) say if you were to rig up
some apparatus which enabled you to flood its case with a stream of
say liquid helium, how much power could you wring out of it? I don\'t
mean theoretically, I mean *practically* taking into account its
real-world limitations. Any idea?

Thanks,

CD

Bipolar transistors don\'t work at liquid helium temps! Better try
liquid nitrogen. Or cold water.

LTSpice includes thermal modelling blocks, you could probably use it to
model liquid cooling loops, too.

Not that it makes much sense in most applications to liquid-cool BJTs.
Maybe in avionics bays in aircraft or on spaceships something.

 

[bitrex]

On 7/26/2020 2:14 PM, Phil Hobbs wrote:

On 2020-07-26 14:06, jlarkin@highlandsniptechnology.com wrote:
On Sun, 26 Jul 2020 17:50:05 +0100, Cursitor Doom
curd@notformail.com> wrote:

Gentlemen,

Taking the 2N3055 as an example (as I\'m sure we\'re all familiar with
this once-ubiquitous decades-old device) say if you were to rig up
some apparatus which enabled you to flood its case with a stream of
say liquid helium, how much power could you wring out of it? I don\'t
mean theoretically, I mean *practically* taking into account its
real-world limitations. Any idea?

Thanks,

CD

Bipolar transistors don\'t work at liquid helium temps! Better try
liquid nitrogen. Or cold water.

You just have to turn the current on before the helium, and do the
measurement fast before you run out of money.

Cheers

Phil Hobbs

Silly thing I did, put a ~70 watt TDP processor in this teeny lil
aluminum box. Thermal epoxied the cooler blocks to the enclosure and
fashioned the right-angle headers from brass plumbing T-joints, solder
and a Dremel. External PSU and coolant pump, just deionized water with
the pump speed under control of the processor temp sensor. 40mm fan at
~700 rpm on the final block.

Box got very toasty but the processor stayed within limits under full load.

<https://www.dropbox.com/s/q8kytisld2w2fls/IMG_20181223_224949148_HDR.jpg?dl=0>

 

[Cursitor Doom]

On Sun, 26 Jul 2020 11:06:48 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sun, 26 Jul 2020 17:50:05 +0100, Cursitor Doom
curd@notformail.com> wrote:

Gentlemen,

Taking the 2N3055 as an example (as I\'m sure we\'re all familiar with
this once-ubiquitous decades-old device) say if you were to rig up
some apparatus which enabled you to flood its case with a stream of
say liquid helium, how much power could you wring out of it? I don\'t
mean theoretically, I mean *practically* taking into account its
real-world limitations. Any idea?

Thanks,

CD

Bipolar transistors don\'t work at liquid helium temps! Better try
liquid nitrogen. Or cold water.

Okay, the liquid helium bit is unworkable for various reasons. Let\'s
be realistic and say forced water cooling. Mount the transistor on a
finned copper heatskink and force water through the fins sufficiently
fast to carry away the excess heat. Under those circs., how many Watts
could be screwed out of it? The normal max dissipation for this device
is 115W and there\'s a datasheet here:

https://www.onsemi.com/pub/Collateral/2N3055-D.PDF


--

Walk away, Boris!

 

[Bill Sloman]

On Monday, July 27, 2020 at 2:50:09 AM UTC+10, Cursitor Doom wrote:

Gentlemen,

Taking the 2N3055 as an example (as I\'m sure we\'re all familiar with
this once-ubiquitous decades-old device) say if you were to rig up
some apparatus which enabled you to flood its case with a stream of
say liquid helium, how much power could you wring out of it? I don\'t
mean theoretically, I mean *practically* taking into account its
real-world limitations. Any idea?

The transistor is a lump of silicon bonded to the metal base of the transistor case. There a thermal resistance from junction to case, more thermal resistance through metal that forms the bottom of the case, and if you clamp the case hard down on the top of a nice thick heat-sink you need a smear of zinc-oxide loaded thermal grease to fill in the air-gaps between the two.

https://alltransistors.com/pdfdatasheet_motorola/2n5684_2n5685_2n5686.pdf

lists the junction to case thermal resistance as 0.584 C/W.

If I remember rightly, the bottom of the case is fairly thick lump of copper, and I used one once to save a design where the original designer had messed up his heat-dissipation calculations.

https://www.onsemi.com/pub/Collateral/2N3055-D.PDF

For the 2N3055 it is 1.52 C/W

The liquid helium would be outside the case. The junction temperature is limited to 200C. Liquid helium boils at -268.75C, so you could get 308W out of a 2N3055, or 801 W out of 2N5685.

You\'d be boiling off a great deal of liquid helium - it\'s heat of vaporisation is 0.0854 kJ/mole, so 801 W is about 10,000 moles per seconds, or 200,000 litres of gas at STP. 4.25K is lot lower than standard temperature, so it\'s 3030 litres of helium gas at -268.75C.

It may not be impracticable - you probably could squirt a high pressure stream of liquid helium at the base of the heat sink and pump away about 3 cubic metres of gas every second - but it certainly wouldn\'t be worth doing.

The 2N3055 is nominally rated at 115W and the 2N5685 at 300W (and you aren\'t going to come close to either figure in a practical set-up).

--
Bill Sloman, Sydney

 

[server]

On Sun, 26 Jul 2020 21:49:52 +0100, Cursitor Doom
<curd@notformail.com> wrote:

On Sun, 26 Jul 2020 11:06:48 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sun, 26 Jul 2020 17:50:05 +0100, Cursitor Doom
curd@notformail.com> wrote:

Gentlemen,

Taking the 2N3055 as an example (as I\'m sure we\'re all familiar with
this once-ubiquitous decades-old device) say if you were to rig up
some apparatus which enabled you to flood its case with a stream of
say liquid helium, how much power could you wring out of it? I don\'t
mean theoretically, I mean *practically* taking into account its
real-world limitations. Any idea?

Thanks,

CD

Bipolar transistors don\'t work at liquid helium temps! Better try
liquid nitrogen. Or cold water.

Okay, the liquid helium bit is unworkable for various reasons. Let\'s
be realistic and say forced water cooling. Mount the transistor on a
finned copper heatskink and force water through the fins sufficiently
fast to carry away the excess heat. Under those circs., how many Watts
could be screwed out of it? The normal max dissipation for this device
is 115W and there\'s a datasheet here:

https://www.onsemi.com/pub/Collateral/2N3055-D.PDF

Based on that data sheet, 115 watts is the max.

But based on the other numbers, if you cool the case to absolute zero,
Tj hits 200C at 311 watts.

If you blast ice cold water directly onto the bottom of the can (no
heat sink needed) it looks like 131 watts to me.

Some 2N5055s had a tiny chip, Fairchild I think, and blew up fast.

We use one fet that\'s claimed to be able to dissipate 1000 watts.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[bitrex]

On 7/26/2020 7:53 PM, Bill Sloman wrote:

On Monday, July 27, 2020 at 2:50:09 AM UTC+10, Cursitor Doom wrote:
Gentlemen,

Taking the 2N3055 as an example (as I\'m sure we\'re all familiar with
this once-ubiquitous decades-old device) say if you were to rig up
some apparatus which enabled you to flood its case with a stream of
say liquid helium, how much power could you wring out of it? I don\'t
mean theoretically, I mean *practically* taking into account its
real-world limitations. Any idea?

The transistor is a lump of silicon bonded to the metal base of the transistor case. There a thermal resistance from junction to case, more thermal resistance through metal that forms the bottom of the case, and if you clamp the case hard down on the top of a nice thick heat-sink you need a smear of zinc-oxide loaded thermal grease to fill in the air-gaps between the two.

https://alltransistors.com/pdfdatasheet_motorola/2n5684_2n5685_2n5686.pdf

lists the junction to case thermal resistance as 0.584 C/W.

If I remember rightly, the bottom of the case is fairly thick lump of copper, and I used one once to save a design where the original designer had messed up his heat-dissipation calculations.

https://www.onsemi.com/pub/Collateral/2N3055-D.PDF

For the 2N3055 it is 1.52 C/W

The liquid helium would be outside the case. The junction temperature is limited to 200C. Liquid helium boils at -268.75C, so you could get 308W out of a 2N3055, or 801 W out of 2N5685.

You\'d be boiling off a great deal of liquid helium - it\'s heat of vaporisation is 0.0854 kJ/mole, so 801 W is about 10,000 moles per seconds, or 200,000 litres of gas at STP. 4.25K is lot lower than standard temperature, so it\'s 3030 litres of helium gas at -268.75C.

It may not be impracticable - you probably could squirt a high pressure stream of liquid helium at the base of the heat sink and pump away about 3 cubic metres of gas every second - but it certainly wouldn\'t be worth doing.

The 2N3055 is nominally rated at 115W and the 2N5685 at 300W (and you aren\'t going to come close to either figure in a practical set-up).

Liquid helium isn\'t particularly cheap either, it\'s a non-renewable
resource, or at least not in large volumes at reasonable cost.

Use liquid hydrogen!

 

[bitrex]

On 7/26/2020 8:09 PM, bitrex wrote:

On 7/26/2020 7:53 PM, Bill Sloman wrote:
On Monday, July 27, 2020 at 2:50:09 AM UTC+10, Cursitor Doom wrote:
Gentlemen,

Taking the 2N3055 as an example (as I\'m sure we\'re all familiar with
this once-ubiquitous decades-old device) say if you were to rig up
some apparatus which enabled you to flood its case with a stream of
say liquid helium, how much power could you wring out of it? I don\'t
mean theoretically, I mean *practically* taking into account its
real-world limitations. Any idea?

The transistor is a lump of silicon bonded to the metal base of the
transistor case. There a thermal resistance from junction to case,
more thermal resistance through metal that forms the bottom of the
case, and if you clamp the case hard down on the top of a nice thick
heat-sink you need a smear of zinc-oxide loaded thermal grease to fill
in the air-gaps between the two.

https://alltransistors.com/pdfdatasheet_motorola/2n5684_2n5685_2n5686.pdf

lists the junction to case thermal resistance as 0.584 C/W.

If I remember rightly, the bottom of the case is fairly thick lump of
copper, and I used one once to save a design where the original
designer had messed up his heat-dissipation calculations.

https://www.onsemi.com/pub/Collateral/2N3055-D.PDF

For the 2N3055 it is 1.52 C/W

The liquid helium would be outside the case. The junction temperature
is limited to 200C. Liquid helium boils at -268.75C, so you could get
308W out of a 2N3055, or 801 W out of 2N5685.

You\'d be boiling off a great deal of liquid helium - it\'s heat of
vaporisation is 0.0854 kJ/mole, so 801 W is about 10,000 moles per
seconds, or 200,000 litres of gas at STP. 4.25K is lot lower than
standard temperature, so it\'s 3030 litres of helium gas at -268.75C.

It may not be impracticable - you probably could squirt a high
pressure stream of liquid helium at the base of the heat sink and pump
away about 3 cubic metres of gas every second - but it certainly
wouldn\'t be worth doing.

The 2N3055 is nominally rated at 115W and the 2N5685 at 300W (and you
aren\'t going to come close to either figure in a practical set-up).


Liquid helium isn\'t particularly cheap either, it\'s a non-renewable
resource, or at least not in large volumes at reasonable cost.

Use liquid hydrogen!

Actually given that it\'s CD asking I expect it\'s some hare-brained
scheme to use power transistors to blow all the world\'s helium reserves
into space to \"prove\" there\'s actually an infinite supply.

 

[Chris Jones]

On 27/07/2020 09:53, Bill Sloman wrote:

On Monday, July 27, 2020 at 2:50:09 AM UTC+10, Cursitor Doom wrote:
Gentlemen,

Taking the 2N3055 as an example (as I\'m sure we\'re all familiar with
this once-ubiquitous decades-old device) say if you were to rig up
some apparatus which enabled you to flood its case with a stream of
say liquid helium, how much power could you wring out of it? I don\'t
mean theoretically, I mean *practically* taking into account its
real-world limitations. Any idea?

The transistor is a lump of silicon bonded to the metal base of the transistor case. There a thermal resistance from junction to case, more thermal resistance through metal that forms the bottom of the case, and if you clamp the case hard down on the top of a nice thick heat-sink you need a smear of zinc-oxide loaded thermal grease to fill in the air-gaps between the two.

https://alltransistors.com/pdfdatasheet_motorola/2n5684_2n5685_2n5686.pdf

lists the junction to case thermal resistance as 0.584 C/W.

If I remember rightly, the bottom of the case is fairly thick lump of copper, and I used one once to save a design where the original designer had messed up his heat-dissipation calculations.

https://www.onsemi.com/pub/Collateral/2N3055-D.PDF

For the 2N3055 it is 1.52 C/W

The liquid helium would be outside the case. The junction temperature is limited to 200C. Liquid helium boils at -268.75C, so you could get 308W out of a 2N3055, or 801 W out of 2N5685.

You\'d be boiling off a great deal of liquid helium - it\'s heat of vaporisation is 0.0854 kJ/mole, so 801 W is about 10,000 moles per seconds, or 200,000 litres of gas at STP. 4.25K is lot lower than standard temperature, so it\'s 3030 litres of helium gas at -268.75C.

It may not be impracticable - you probably could squirt a high pressure stream of liquid helium at the base of the heat sink and pump away about 3 cubic metres of gas every second - but it certainly wouldn\'t be worth doing.

The 2N3055 is nominally rated at 115W and the 2N5685 at 300W (and you aren\'t going to come close to either figure in a practical set-up).

I saw a design once where they carefully drilled a hole in the top of
the TO-3 case, and soldered in a pipe with a nozzle pointed right at the
face of the die, and another pipe was soldered to an outlet hole
somewhere at the edge of the TO-3 can. I think it was a German project
but can\'t recall.

By spraying or squirting an inert, insulating coolant (fluorinert or
maybe transformer oil, or a low-boiling-point liquid e.g. butane or
freon) right at the surface of the die, it ought to be possible to
ignore the junction-to-case thermal resistance and also to exceed the
usual current capacity of the bondwires.

I am dubious of the long-term reliability of such a scheme, and I\'m not
aware of any magic device in TO-3 that couldn\'t be replaced by multiple
parts in a different package on a water-cooled heatsink, but if you had
to do it, I expect it would work for a while. If you could do it with
some fancy RF power amplifier part it might be worth it, but they
generally don\'t come in TO-3.

 

[Cursitor Doom]

On Sun, 26 Jul 2020 17:00:19 -0700, jlarkin@highlandsniptechnology.com
wrote:

Based on that data sheet, 115 watts is the max.

But based on the other numbers, if you cool the case to absolute zero,
Tj hits 200C at 311 watts.

I guess that\'s the killer here: the junction temp.

If you blast ice cold water directly onto the bottom of the can (no
heat sink needed) it looks like 131 watts to me.

Some 2N5055s had a tiny chip, Fairchild I think, and blew up fast.

We use one fet that\'s claimed to be able to dissipate 1000 watts.

Does it?

 

[Bill Sloman]

On Monday, July 27, 2020 at 10:14:51 AM UTC+10, bitrex wrote:

On 7/26/2020 8:09 PM, bitrex wrote:
On 7/26/2020 7:53 PM, Bill Sloman wrote:
On Monday, July 27, 2020 at 2:50:09 AM UTC+10, Cursitor Doom wrote:
Gentlemen,

Taking the 2N3055 as an example (as I\'m sure we\'re all familiar with
this once-ubiquitous decades-old device) say if you were to rig up
some apparatus which enabled you to flood its case with a stream of
say liquid helium, how much power could you wring out of it? I don\'t
mean theoretically, I mean *practically* taking into account its
real-world limitations. Any idea?

The transistor is a lump of silicon bonded to the metal base of the
transistor case. There a thermal resistance from junction to case,
more thermal resistance through metal that forms the bottom of the
case, and if you clamp the case hard down on the top of a nice thick
heat-sink you need a smear of zinc-oxide loaded thermal grease to fill
in the air-gaps between the two.

https://alltransistors.com/pdfdatasheet_motorola/2n5684_2n5685_2n5686.pdf

lists the junction to case thermal resistance as 0.584 C/W.

If I remember rightly, the bottom of the case is fairly thick lump of
copper, and I used one once to save a design where the original
designer had messed up his heat-dissipation calculations.

https://www.onsemi.com/pub/Collateral/2N3055-D.PDF

For the 2N3055 it is 1.52 C/W

The liquid helium would be outside the case. The junction temperature
is limited to 200C. Liquid helium boils at -268.75C, so you could get
308W out of a 2N3055, or 801 W out of 2N5685.

You\'d be boiling off a great deal of liquid helium - it\'s heat of
vaporisation is 0.0854 kJ/mole, so 801 W is about 10,000 moles per
seconds, or 200,000 litres of gas at STP. 4.25K is lot lower than
standard temperature, so it\'s 3030 litres of helium gas at -268.75C.

It may not be impracticable - you probably could squirt a high
pressure stream of liquid helium at the base of the heat sink and pump
away about 3 cubic metres of gas every second - but it certainly
wouldn\'t be worth doing.

The 2N3055 is nominally rated at 115W and the 2N5685 at 300W (and you
aren\'t going to come close to either figure in a practical set-up).


Liquid helium isn\'t particularly cheap either, it\'s a non-renewable
resource, or at least not in large volumes at reasonable cost.

You recirculate it in any practical set-up - recondense it and pump it back

> > Use liquid hydrogen!

Fine until it leaks - mixture of hydrogen gas and air are explosive over a very wide range of concentrations.

Actually given that it\'s CD asking I expect it\'s some hare-brained
scheme to use power transistors to blow all the world\'s helium reserves
into space to \"prove\" there\'s actually an infinite supply.

Cursitor Doom isn\'t hare-brained - that would be unkind to hares. He\'s just a rather nasty half-wit who cuts and pastes a lot of nonsense that he doesn\'t actually understand.

--
Bill Sloman, Sydney

 

[Phil Allison]

jla...@highlandsniptechnology.com wrote:

===========================================

Some 2N5055s had a tiny chip, Fairchild I think, and blew up fast.

** So did Motorola, when back they used Aluminium paks.

Same devices had a short thermal cycle life and by the mid 80s they returned to using steel paks with the chip sitting chip on an alloy slug.

Most other 3055s had far larger chips, eg RCA, while the small chips boasted a higher Ft.

Because of the JEDEC numbering system and rules, any TO3 device which met or exceeded JEDEC specs of a 2N3055 could be labelled as one.

https://en.wikipedia.org/wiki/JEDEC




..... Phil

 

[Phil Allison]

Cursitor Doom wrote:

=======================

Taking the 2N3055 as an example (as I\'m sure we\'re all familiar with
this once-ubiquitous decades-old device) say if you were to rig up
some apparatus which enabled you to flood its case with a stream of
say liquid helium, how much power could you wring out of it? I don\'t
mean theoretically, I mean *practically* taking into account its
real-world limitations. Any idea?

** Q, \"wring out of it \" = what ?

The makers rating is for dissipation, nothing else.

As a linear PSU regulator, it might realistically deliver 8 amps at 60 volts = 480W of useful DC.

Use a pair in a push pull class B stage and you can have 100W at 4 ohms with about 40W dissipation per device at worst case sine wave.


..... Phil
..... Phil

 

[Tony Stewart]

On Sun. 26 Jul.-20 7:53 p.m., Bill Sloman wrote:

On Monday, July 27, 2020 at 2:50:09 AM UTC+10, Cursitor Doom wrote:
Gentlemen,

Taking the 2N3055 as an example (as I\'m sure we\'re all familiar with
this once-ubiquitous decades-old device) say if you were to rig up
some apparatus which enabled you to flood its case with a stream of
say liquid helium, how much power could you wring out of it? I don\'t
mean theoretically, I mean *practically* taking into account its
real-world limitations. Any idea?

The transistor is a lump of silicon bonded to the metal base of the transistor case. There a thermal resistance from junction to case, more thermal resistance through metal that forms the bottom of the case, and if you clamp the case hard down on the top of a nice thick heat-sink you need a smear of zinc-oxide loaded thermal grease to fill in the air-gaps between the two.

https://alltransistors.com/pdfdatasheet_motorola/2n5684_2n5685_2n5686.pdf

lists the junction to case thermal resistance as 0.584 C/W.

If I remember rightly, the bottom of the case is fairly thick lump of copper, and I used one once to save a design where the original designer had messed up his heat-dissipation calculations.

https://www.onsemi.com/pub/Collateral/2N3055-D.PDF

For the 2N3055 it is 1.52 C/W

The liquid helium would be outside the case. The junction temperature is limited to 200C. Liquid helium boils at -268.75C, so you could get 308W out of a 2N3055, or 801 W out of 2N5685.

You\'d be boiling off a great deal of liquid helium - it\'s heat of vaporisation is 0.0854 kJ/mole, so 801 W is about 10,000 moles per seconds, or 200,000 litres of gas at STP. 4.25K is lot lower than standard temperature, so it\'s 3030 litres of helium gas at -268.75C.

It may not be impracticable - you probably could squirt a high pressure stream of liquid helium at the base of the heat sink and pump away about 3 cubic metres of gas every second - but it certainly wouldn\'t be worth doing.

The 2N3055 is nominally rated at 115W and the 2N5685 at 300W (and you aren\'t going to come close to either figure in a practical set-up).

I agree.

The limit could be inside the chip but ON Semi says with thermal greased
bare metal contact you can get the junction to case thermal resistance
down to 0.1 W/\'C if you can manage rated torque or make a contact
pressure > 200 PSI to heatsink.

I\'ve used crushed dry ice with a muffin fan inside a picnic box to test
products down to -45\'C but contact pressure and out gassing won\'t give
you great thermal resistance to the dry ice. So I used forced air inside
while generating 3W and used thermocouples on the D.U.T.

https://www.onsemi.com/pub/Collateral/AN1040-D.PDF

 

[server]

On Sun, 26 Jul 2020 17:00:19 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sun, 26 Jul 2020 21:49:52 +0100, Cursitor Doom
curd@notformail.com> wrote:

On Sun, 26 Jul 2020 11:06:48 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sun, 26 Jul 2020 17:50:05 +0100, Cursitor Doom
curd@notformail.com> wrote:

Gentlemen,

Taking the 2N3055 as an example (as I\'m sure we\'re all familiar with
this once-ubiquitous decades-old device) say if you were to rig up
some apparatus which enabled you to flood its case with a stream of
say liquid helium, how much power could you wring out of it? I don\'t
mean theoretically, I mean *practically* taking into account its
real-world limitations. Any idea?

Thanks,

CD

Bipolar transistors don\'t work at liquid helium temps! Better try
liquid nitrogen. Or cold water.

Okay, the liquid helium bit is unworkable for various reasons. Let\'s
be realistic and say forced water cooling. Mount the transistor on a
finned copper heatskink and force water through the fins sufficiently
fast to carry away the excess heat. Under those circs., how many Watts
could be screwed out of it? The normal max dissipation for this device
is 115W and there\'s a datasheet here:

https://www.onsemi.com/pub/Collateral/2N3055-D.PDF

Based on that data sheet, 115 watts is the max.

But based on the other numbers, if you cool the case to absolute zero,
Tj hits 200C at 311 watts.

If you blast ice cold water directly onto the bottom of the can (no
heat sink needed) it looks like 131 watts to me.

Some 2N5055s had a tiny chip, Fairchild I think, and blew up fast.

On the old days the story was that when a manufacturer tried to make
some high quality power transistors, but some chips did not meet the
original parameters (such as h_FE or f_T) but exceeded the very
relaxed 2N3055 requirements, these were sold as 2N3055 transistors.
This is usually OK, but some manufacturers labeled some VHF power
transistors as 2N3055. However, when installed into a typical LF
circuit layout, the transistor might oscillate wildly somewhere in VHF
or UHF .

We use one fet that\'s claimed to be able to dissipate 1000 watts.