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OT: Power BJT Power Limit

Started by Cursitor Doom July 26, 2020
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
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
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
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
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
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
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.
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>
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!
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