IR is insane
in [Design]
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From: krw on 21 Mar 2010 18:42 On Sun, 21 Mar 2010 10:43:02 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Sat, 20 Mar 2010 18:09:39 -0500, "krw(a)att.bizzzzzzzzzzzz" <krw(a)att.bizzzzzzzzzzzz> wrote: > >>On Sat, 20 Mar 2010 12:12:14 -0700, Archimedes' Lever >><OneBigLever(a)InfiniteSeries.Org> wrote: >> >>>On Sat, 20 Mar 2010 10:56:18 -0700, John Larkin >>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>>>Boiling liquid carries away far more heat than still or even flowing >>>>liquid. Since IR cheats as hard as they can, we can assume they used >>>>boiling liquid. I fact, they say so. >>> >>> >>> Chilled fluorinert does not need to be boiling to have thermal >>>efficiency. >> >>Wrong again, AlwaysWrong. How do you think Fluorinert works? By magic? > >While i have seen Flourinert cooling maybe half a dozen times, only once was >it used in phase change mode. I mostly saw circulated chilled liquid baths. >Works real good for temperature stabilizing standard resistors. *Every* time I've seen it used there was a phase change somewhere in the process. There are a *lot* of cheaper and better alternatives if a lowish temper phase change isn't needed. Fluorinert doesn't have a stellar specific heat.
From: John Fields on 22 Mar 2010 10:35 On Sun, 21 Mar 2010 10:14:57 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote: >On Fri, 19 Mar 2010 11:05:14 -0500, John Fields <jfields(a)austininstruments.com> wrote: > >>On Fri, 19 Mar 2010 07:16:29 -0700, John Larkin >><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>IR does insane things. The flyer I got spec'd the max current (340 >>>amps!) and Rds-on different from the part datasheet (270 amps, or 195 >>>amps "package limited")... all or which are preposterous for a dpak. >>> >>>When people play games like that, I don't buy their parts. >> >>--- >>Oh, well, it's your loss... >> >>60Vdss, Rds(on)max 2.5milliohms, 375 watts @25C Tc, it's a nice part. >> >>JF > >Well JF, what is the typical theta(jc) of a dpak? --- For IR, about 4K/W. --- >This sounds like a really crazy infinite heat sink driven by LN2. --- Could be, but if you're not willing to go to those extremes and you want to use it "conventionally" it's still not a bad part, huh? JF
From: Don Klipstein on 22 Mar 2010 16:11 In article <410aq5pjiu4e0ig8j1s10hhfmohnu9o9n6(a)4ax.com>, John Larkin wrote: >On 20 Mar 2010 14:15:15 GMT, Glen Walpert <nospam(a)null.void> wrote: > >>On Sat, 20 Mar 2010 07:24:54 +0000, Don Klipstein wrote: >>(In short, plenty including:) >>ISTR a previous thread where someone turned up a maximum current test >>procedure where the device was submerged in a "phase change fluid" for >>the peak current test. Not a fluid cooled heatsink; direct immersion of >>the device. >><SNIP more along these lines to edit for space> >I haven't done the math on this, but I suspect the source lead would >vaporize at 195 amps, much less 340. If it were immersed in a boiling >liquid, it would probably be OK. I think that's how they test them. I got into a mood to try the math on this. Back to the datasheet, http://www.irf.com/product-info/datasheets/data/irfs3006pbf.pdf My eyeball-estimate of the length of the source lead, between the solder joint and the bonding wire, is 8 mm, about half with a narrow portion (datasheet says .51 by .38 mm minimum), and about half with a wide portion (datasheet says 1.14 by .38 mm minimum). Wikipedia says the resistivity of copper at 20 C is 1.72E-8 ohm-meter, which is 1.72E-5 ohm-mm. I would like a 75 C figure, which is 19.5% higher, and that is 2.055E-5 ohm-mm. From here, I get .425 milliohm for the narrow half and .19 milliohm for the wide half, for a total of .515 milliohm. .000515 times square of 195 amps is 19.6 watts. That sounds unreasonable to me. I seem to think that the narrow part of the source lead will melt. Try for the wide half alone: .00019 ohm times square of 195 amps is 7.2 watts. Repeat for 170 amps, and that is 5.5 watts. That sounds to me able to be heatsunk from the source lead by soldering big fat wire to the wide part of the source lead, but it also sounds to me sort of insane to package such a big MOSFET with such requirements in such a small package. - Don Klipstein (don(a)misty.com)
From: JosephKK on 23 Mar 2010 01:28 On Mon, 22 Mar 2010 09:35:30 -0500, John Fields <jfields(a)austininstruments.com> wrote: >On Sun, 21 Mar 2010 10:14:57 -0700, "JosephKK"<quiettechblue(a)yahoo.com> >wrote: > >>On Fri, 19 Mar 2010 11:05:14 -0500, John Fields <jfields(a)austininstruments.com> wrote: >> >>>On Fri, 19 Mar 2010 07:16:29 -0700, John Larkin >>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: > > >>>>IR does insane things. The flyer I got spec'd the max current (340 >>>>amps!) and Rds-on different from the part datasheet (270 amps, or 195 >>>>amps "package limited")... all or which are preposterous for a dpak. >>>> >>>>When people play games like that, I don't buy their parts. >>> >>>--- >>>Oh, well, it's your loss... >>> >>>60Vdss, Rds(on)max 2.5milliohms, 375 watts @25C Tc, it's a nice part. >>> >>>JF >> >>Well JF, what is the typical theta(jc) of a dpak? > >--- >For IR, about 4K/W. >--- > >>This sounds like a really crazy infinite heat sink driven by LN2. > >--- >Could be, but if you're not willing to go to those extremes and you want >to use it "conventionally" it's still not a bad part, huh? > >JF I certainly might, though companies that use specsmanship that radically do not inspire my trust. Plus i hate fighting through datasheet gibberish to get realistic properties; which gibberish, when detected, will almost always make me change vendors. I do not want to spend the time to get past obvious baloney to find out what the part can do in normal use.
From: JosephKK on 23 Mar 2010 01:39
On Sun, 21 Mar 2010 11:52:41 -0700, WarmUnderbelly <WarmUnderbellyOfAmerica(a)thebarattheendoftheuniverse.org> wrote: >On Sun, 21 Mar 2010 10:43:02 -0700, "JosephKK"<quiettechblue(a)yahoo.com> >wrote: > >>On Sat, 20 Mar 2010 18:09:39 -0500, "krw(a)att.bizzzzzzzzzzzz" <krw(a)att.bizzzzzzzzzzzz> wrote: >> >>>On Sat, 20 Mar 2010 12:12:14 -0700, Archimedes' Lever >>><OneBigLever(a)InfiniteSeries.Org> wrote: >>> >>>>On Sat, 20 Mar 2010 10:56:18 -0700, John Larkin >>>><jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >>>> >>>>>Boiling liquid carries away far more heat than still or even flowing >>>>>liquid. Since IR cheats as hard as they can, we can assume they used >>>>>boiling liquid. I fact, they say so. >>>> >>>> >>>> Chilled fluorinert does not need to be boiling to have thermal >>>>efficiency. >>> >>>Wrong again, AlwaysWrong. How do you think Fluorinert works? By magic? >> >>While i have seen Flourinert cooling maybe half a dozen times, only once was >>it used in phase change mode. I mostly saw circulated chilled liquid baths. >>Works real good for temperature stabilizing standard resistors. > > > It is also a good media, if chilled, for cooling a PC for the >overclocker crowd. > > I would like to put a PC motherboard in a fish tank full of it to freak >people out with. Fish tank, maybe $250, chiller (repurposed small refrigerator) maybe $200 15 gallons Flourinert $600. Will you get $1050 plus time modifying the refrigerator of entertainment out of it? Hiding all the mods and holding the Flourinert at 3 C or less is easily and extra $300 in materials. If you are wiling to put some effort in moisture protection for the tank, you could drop the fluid temperature to about -40 C and OC the hell out the computer. |