On a sunny day (Fri, 23 Jan 2015 12:36:54 -0800 (PST)) it happened George Herold <gherold@teachspin.com> wrote in <c4eb58c6-721f-4bc5-84dd-55d3e3b32816@googlegroups.com>:>On Friday, January 23, 2015 at 11:45:16 AM UTC-5, Jan Panteltje wrote: >> On a sunny day (Fri, 23 Jan 2015 07:54:21 -0800 (PST)) it happened George >> Herold <gherold@teachspin.com> wrote in >> <9263cc76-7046-4a61-8a13-280fc4c0d917@googlegroups.com>: >> >> >OK first the numbers are almost too good to believe, but here they are. >> >(I only tested 4 FET's I had to solder wires on to go down into the dewar. The first one I had clip leads, but the dang >> >thick >> >plastic on the leads froze up, and I was afraid I'd have to break it to get it back out of the dewar neck.) >> > >> > V V >> > Room temp. 77K >> >0.5500 1.0154 >> >0.5504 1.0156 >> >0.5508 1.0157 >> >0.5509 1.0159 >> >> What current did you use? Any self-heating? > >This was with my fluke DMM (I think ~ 1mA) > >George H.OK, thanks.
estimating junction temperature of a power mosfet
Started by ●January 21, 2015
Reply by ●January 24, 20152015-01-24
Reply by ●January 24, 20152015-01-24
On 23/01/2015 23:31, Alain Coste wrote:> Thank you John for the interesting information. The use of mosfets in linear > mode is not very common, and it's more difficult to find data than for > switch mode. > >> It often makes sense to use more fets, spread out over the heatsink >> surface, especially if the baseplate part of the heat sink is thin, >> namely has high thermal spreading resistance. >> >> This uses copper heat spreaders to transfer the heat into the aluminum >> sink. >> >> https://dl.dropboxusercontent.com/u/53724080/Thermal/Amp.jpg >> > > Now I see what to use _more_ fets means... > For my electronic load I could have used more transistors, but this > increases the number of current sense resistors and operational amplifiers > to control them. For the power I wanted (400 .. 420W), I thought that two > mosfets was a good compromise.> [...] I am building an electronic load using a single IXTN60N50L2. It uses an unconventional control scheme which in my case was easier to do with a single large mosfet than with many small ones. I am cooling the MOSFET with liquid. I was very surprised that nobody seems to sell water blocks already drilled for SOT-227 packages. I expect that if I drilled the required mounting holes on any of the widely available CPU or GPU water blocks, the drill would hit a water channel and it would leak. Therefore I expect I'll have to make my own water block. Chris
Reply by ●January 24, 20152015-01-24
On Sat, 24 Jan 2015 23:57:24 +1100, Chris Jones <lugnut808@spam.yahoo.com> wrote:>On 23/01/2015 23:31, Alain Coste wrote: >> Thank you John for the interesting information. The use of mosfets in linear >> mode is not very common, and it's more difficult to find data than for >> switch mode. >> >>> It often makes sense to use more fets, spread out over the heatsink >>> surface, especially if the baseplate part of the heat sink is thin, >>> namely has high thermal spreading resistance. >>> >>> This uses copper heat spreaders to transfer the heat into the aluminum >>> sink. >>> >>> https://dl.dropboxusercontent.com/u/53724080/Thermal/Amp.jpg >>> >> >> Now I see what to use _more_ fets means... >> For my electronic load I could have used more transistors, but this >> increases the number of current sense resistors and operational amplifiers >> to control them. For the power I wanted (400 .. 420W), I thought that two >> mosfets was a good compromise. > > [...] > > >I am building an electronic load using a single IXTN60N50L2. It uses an >unconventional control scheme which in my case was easier to do with a >single large mosfet than with many small ones. I am cooling the MOSFET >with liquid. I was very surprised that nobody seems to sell water blocks >already drilled for SOT-227 packages. I expect that if I drilled the >required mounting holes on any of the widely available CPU or GPU water >blocks, the drill would hit a water channel and it would leak. Therefore >I expect I'll have to make my own water block. > >ChrisMcMaster sells cold plates, cheap compared to most others. No problem drilling this kind. https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Coldplate.jpg https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Water_Cooled_Pulser.jpg https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Copper.jpg -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●January 24, 20152015-01-24
On Sat, 24 Jan 2015 10:14:05 GMT, Jan Panteltje <panteltje@yahoo.com> wrote:>On a sunny day (Fri, 23 Jan 2015 14:35:30 -0800) it happened John Larkin ><jlarkin@highlandtechnology.com> wrote in ><j2j5calp70pu1pk7trqdg2kq74ffhbj2qf@4ax.com>: > >>On Fri, 23 Jan 2015 16:45:23 GMT, Jan Panteltje <panteltje@yahoo.com> >>wrote: >> >>>On a sunny day (Fri, 23 Jan 2015 07:54:21 -0800 (PST)) it happened George >>>Herold <gherold@teachspin.com> wrote in >>><9263cc76-7046-4a61-8a13-280fc4c0d917@googlegroups.com>: >>> >>>>OK first the numbers are almost too good to believe, but here they are. >>>>(I only tested 4 FET's I had to solder wires on to go down into the dewar. The first one I had clip leads, but the dang thick >>>>plastic on the leads froze up, and I was afraid I'd have to break it to get it back out of the dewar neck.) >>>> >>>> V V >>>> Room temp. 77K >>>>0.5500 1.0154 >>>>0.5504 1.0156 >>>>0.5508 1.0157 >>>>0.5509 1.0159 >>> >>>What current did you use? Any self-heating? >> >>Cryo-diodes are usually run at 10 uA, but a big mosfet in LN2 probably >>doesn't self-heat much. > >1.0159 > ^ >Well he is specifying at 10^-4 say 100 ppm.... >:-) > >10uA would probably be OK though, 10uW * Rtj >:-) > >Math OK?At LN2 temp, the tempco is probably around 2 mV/K, so he's seeing really good repeatability. PN silicon diodes act like diodes down to about 20K. Below that the voltage drop goes way up and they get more resistive, but less predictable. Some companies, like Lakeshore, test diodes down to liquid helium temps and sell parts with dependable curves. Thermal conductivities go to hell at those temps, hence the 10 uA convention. A big mosfet in boiling LN2 is going to be very well temperature pinned, at least short-term, as long as the LN2 stays LN2. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●January 25, 20152015-01-25
On a sunny day (Sat, 24 Jan 2015 09:40:16 -0800) it happened John Larkin <jlarkin@highlandtechnology.com> wrote in <jnl7cadm33hf00saar3grl0lku1sjc8otd@4ax.com>:>McMaster sells cold plates, cheap compared to most others. No problem >drilling this kind. > >https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Coldplate.jpg > >https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Water_Cooled_Pulser.jpg > >https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Copper.jpgNice! Is that the temp sensor in the back of thr last jpg with the black wires? I am using a BJT as temp sensor here: http://panteltje.com/panteltje/tri_pic/tritium_decay_experiment_black_box_electronics_top_view_IMG_3873.GIF How about this for cooling? http://panteltje.com/pub/tri_pic_with_the_icecream-and_pizzas_IMG_3494.JPG
Reply by ●January 25, 20152015-01-25
On 25/01/2015 04:40, John Larkin wrote:> On Sat, 24 Jan 2015 23:57:24 +1100, Chris Jones > <lugnut808@spam.yahoo.com> wrote: > >> On 23/01/2015 23:31, Alain Coste wrote: >>> Thank you John for the interesting information. The use of mosfets in linear >>> mode is not very common, and it's more difficult to find data than for >>> switch mode. >>> >>>> It often makes sense to use more fets, spread out over the heatsink >>>> surface, especially if the baseplate part of the heat sink is thin, >>>> namely has high thermal spreading resistance. >>>> >>>> This uses copper heat spreaders to transfer the heat into the aluminum >>>> sink. >>>> >>>> https://dl.dropboxusercontent.com/u/53724080/Thermal/Amp.jpg >>>> >>> >>> Now I see what to use _more_ fets means... >>> For my electronic load I could have used more transistors, but this >>> increases the number of current sense resistors and operational amplifiers >>> to control them. For the power I wanted (400 .. 420W), I thought that two >>> mosfets was a good compromise. >>> [...] >> >> >> I am building an electronic load using a single IXTN60N50L2. It uses an >> unconventional control scheme which in my case was easier to do with a >> single large mosfet than with many small ones. I am cooling the MOSFET >> with liquid. I was very surprised that nobody seems to sell water blocks >> already drilled for SOT-227 packages. I expect that if I drilled the >> required mounting holes on any of the widely available CPU or GPU water >> blocks, the drill would hit a water channel and it would leak. Therefore >> I expect I'll have to make my own water block. >> >> Chris > > McMaster sells cold plates, cheap compared to most others. No problem > drilling this kind. > > https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Coldplate.jpg > > https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Water_Cooled_Pulser.jpg > > https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Copper.jpg > >Thanks. Since the "cooling" fluid that I will get arrives already at about 70 deg C, and I want to dissipate a lot of power, I want very low thermal resistance, so I think I will use something made from copper. I also need it to be not much bigger than the SOT-227 package because of the mechanical constraints. I would like to find something already made for this package, but otherwise I might as well silver-braze some pipes into a block of copper - either into grooves made with a ball-end mill, or drill long holes right through the copper (yuck!), drill manifolds in the other direction, and braze plugs into the unnecessary holes and braze on inlet and outlet pipes, then mill the mounting surface flat. I only need a couple of them. If I could buy a small version of this CP25 thing with threaded inserts in the right place for SOT-227 then I would be tempted: http://www.amstechnologies.com/products/thermal-management/liquid-cooling/cold-plates/vacuum-brazed-flat-tube-pin-fin-cold-plates/view/extended-surface-iiTM-cp25/ Chris
Reply by ●January 25, 20152015-01-25
On Sun, 25 Jan 2015 11:16:34 GMT, Jan Panteltje <panteltje@yahoo.com> wrote:>On a sunny day (Sat, 24 Jan 2015 09:40:16 -0800) it happened John Larkin ><jlarkin@highlandtechnology.com> wrote in ><jnl7cadm33hf00saar3grl0lku1sjc8otd@4ax.com>: > >>McMaster sells cold plates, cheap compared to most others. No problem >>drilling this kind. >> >>https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Coldplate.jpg >> >>https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Water_Cooled_Pulser.jpg >> >>https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Copper.jpg > >Nice! >Is that the temp sensor in the back of thr last jpg with the black wires?Yup, it's a snap switch type. Shuts things off if we lose cooling.> >I am using a BJT as temp sensor here: > http://panteltje.com/panteltje/tri_pic/tritium_decay_experiment_black_box_electronics_top_view_IMG_3873.GIFWell, that's one breadboarding style. https://dl.dropboxusercontent.com/u/53724080/Protos/D200_BB_4.JPG LM35s are nice temp sensors. Or thinfilm RTDs. https://dl.dropboxusercontent.com/u/53724080/Thermal/RTD_outside.jpg -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●January 25, 20152015-01-25
On a sunny day (Sun, 25 Jan 2015 08:00:32 -0800) it happened John Larkin <jlarkin@highlandtechnology.com> wrote in <674acah94ih10mmk3ovtq884tf6p3cdb79@4ax.com>:>On Sun, 25 Jan 2015 11:16:34 GMT, Jan Panteltje <panteltje@yahoo.com> >wrote: > >>On a sunny day (Sat, 24 Jan 2015 09:40:16 -0800) it happened John Larkin >><jlarkin@highlandtechnology.com> wrote in >><jnl7cadm33hf00saar3grl0lku1sjc8otd@4ax.com>: >> >>>McMaster sells cold plates, cheap compared to most others. No problem >>>drilling this kind. >>> >>>https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Coldplate.jpg >>> >>>https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Water_Cooled_Pulser.jpg >>> >>>https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Copper.jpg >> >>Nice! >>Is that the temp sensor in the back of thr last jpg with the black wires? > >Yup, it's a snap switch type. Shuts things off if we lose cooling. > >> >>I am using a BJT as temp sensor here: >> http://panteltje.com/panteltje/tri_pic/tritium_decay_experiment_black_box_electronics_top_view_IMG_3873.GIF > >Well, that's one breadboarding style.Breadboard now been working 24/7 for > 2 years, say 2.5 years. temp control has been within a half degree C or so all the time. As _relative_ sensors these transistor junctions are great.>https://dl.dropboxusercontent.com/u/53724080/Protos/D200_BB_4.JPGIt looks so expensive it scares me to solder on it...>LM35s are nice temp sensors. Or thinfilm RTDs. > >https://dl.dropboxusercontent.com/u/53724080/Thermal/RTD_outside.jpgYes I have some, or was it LM135 or LM335 is use cold side sensor on my thermocouple amplifier http://panteltje.com/pub/thermocouple_interface_with_sunshade_IMG_3394.JPG it is next to the trimpot, I used the adjustment lead of the LM. In action here with the cryo-cooler: http://panteltje.com/pub/cryo/
Reply by ●January 25, 20152015-01-25
On Sun, 25 Jan 2015 22:37:06 +1100, Chris Jones <lugnut808@spam.yahoo.com> wrote:>On 25/01/2015 04:40, John Larkin wrote: >> On Sat, 24 Jan 2015 23:57:24 +1100, Chris Jones >> <lugnut808@spam.yahoo.com> wrote: >> >>> On 23/01/2015 23:31, Alain Coste wrote: >>>> Thank you John for the interesting information. The use of mosfets in linear >>>> mode is not very common, and it's more difficult to find data than for >>>> switch mode. >>>> >>>>> It often makes sense to use more fets, spread out over the heatsink >>>>> surface, especially if the baseplate part of the heat sink is thin, >>>>> namely has high thermal spreading resistance. >>>>> >>>>> This uses copper heat spreaders to transfer the heat into the aluminum >>>>> sink. >>>>> >>>>> https://dl.dropboxusercontent.com/u/53724080/Thermal/Amp.jpg >>>>> >>>> >>>> Now I see what to use _more_ fets means... >>>> For my electronic load I could have used more transistors, but this >>>> increases the number of current sense resistors and operational amplifiers >>>> to control them. For the power I wanted (400 .. 420W), I thought that two >>>> mosfets was a good compromise. >>>> [...] >>> >>> >>> I am building an electronic load using a single IXTN60N50L2. It uses an >>> unconventional control scheme which in my case was easier to do with a >>> single large mosfet than with many small ones. I am cooling the MOSFET >>> with liquid. I was very surprised that nobody seems to sell water blocks >>> already drilled for SOT-227 packages. I expect that if I drilled the >>> required mounting holes on any of the widely available CPU or GPU water >>> blocks, the drill would hit a water channel and it would leak. Therefore >>> I expect I'll have to make my own water block. >>> >>> Chris >> >> McMaster sells cold plates, cheap compared to most others. No problem >> drilling this kind. >> >> https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Coldplate.jpg >> >> https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Water_Cooled_Pulser.jpg >> >> https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Copper.jpg >> >> > >Thanks. Since the "cooling" fluid that I will get arrives already at >about 70 deg C, and I want to dissipate a lot of power, I want very low >thermal resistance, so I think I will use something made from copper. I >also need it to be not much bigger than the SOT-227 package because of >the mechanical constraints. I would like to find something already made >for this package, but otherwise I might as well silver-braze some pipes >into a block of copper - either into grooves made with a ball-end mill, >or drill long holes right through the copper (yuck!), drill manifolds in >the other direction, and braze plugs into the unnecessary holes and >braze on inlet and outlet pipes, then mill the mounting surface flat. I >only need a couple of them. > >If I could buy a small version of this CP25 thing with threaded inserts >in the right place for SOT-227 then I would be tempted: >http://www.amstechnologies.com/products/thermal-management/liquid-cooling/cold-plates/vacuum-brazed-flat-tube-pin-fin-cold-plates/view/extended-surface-iiTM-cp25/ > >Chris >You could get a small copper block and solder a zigzag copper tube to it. Mill some channels first maybe, like the one in my pic. Low hassle level, except that copper is a bitch to machine. We use Alloy 110, not quite as gummy as soft copper. Alloys generally have much reduced electrical and thermal conductivity. One GPM has a net theta of 0.0037 K/W, so you don't need much water flow to cool a few hundred watts of mosfet. Water has a very high specific heat, which is why long hot showers are expensive. But worth it. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●January 25, 20152015-01-25
On Sun, 25 Jan 2015 17:04:03 GMT, Jan Panteltje <panteltje@yahoo.com> wrote:>On a sunny day (Sun, 25 Jan 2015 08:00:32 -0800) it happened John Larkin ><jlarkin@highlandtechnology.com> wrote in ><674acah94ih10mmk3ovtq884tf6p3cdb79@4ax.com>: > >>On Sun, 25 Jan 2015 11:16:34 GMT, Jan Panteltje <panteltje@yahoo.com> >>wrote: >> >>>On a sunny day (Sat, 24 Jan 2015 09:40:16 -0800) it happened John Larkin >>><jlarkin@highlandtechnology.com> wrote in >>><jnl7cadm33hf00saar3grl0lku1sjc8otd@4ax.com>: >>> >>>>McMaster sells cold plates, cheap compared to most others. No problem >>>>drilling this kind. >>>> >>>>https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Coldplate.jpg >>>> >>>>https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Water_Cooled_Pulser.jpg >>>> >>>>https://dl.dropboxusercontent.com/u/53724080/Thermal/T222_Copper.jpg >>> >>>Nice! >>>Is that the temp sensor in the back of thr last jpg with the black wires? >> >>Yup, it's a snap switch type. Shuts things off if we lose cooling. >> >>> >>>I am using a BJT as temp sensor here: >>> http://panteltje.com/panteltje/tri_pic/tritium_decay_experiment_black_box_electronics_top_view_IMG_3873.GIF >> >>Well, that's one breadboarding style. > >Breadboard now been working 24/7 for > 2 years, say 2.5 years. >temp control has been within a half degree C or so all the time. >As _relative_ sensors these transistor junctions are great. > > >>https://dl.dropboxusercontent.com/u/53724080/Protos/D200_BB_4.JPG > >It looks so expensive it scares me to solder on it...Gold plated FR4, never tarnishes, wonderful to solder. Cost me $100 per square foot, but a square foot makes a lot of breadboards.> > >>LM35s are nice temp sensors. Or thinfilm RTDs. >> >>https://dl.dropboxusercontent.com/u/53724080/Thermal/RTD_outside.jpg > >Yes I have some, or was it LM135 or LM335 is use cold side sensor on my thermocouple amplifier > http://panteltje.com/pub/thermocouple_interface_with_sunshade_IMG_3394.JPG >it is next to the trimpot, I used the adjustment lead of the LM. >In action here with the cryo-cooler: > http://panteltje.com/pub/cryo/The semiconductor sensors are convenient but not super accurate. We've found the thinfilm RTDs to generally be very accurate, for t/c reference junction sensing and such. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
