On Friday, January 23, 2015 at 8:31:21 AM UTC-5, George Herold wrote:> On Thursday, January 22, 2015 at 3:18:56 PM UTC-5, John Larkin wrote: > > On Thu, 22 Jan 2015 11:56:15 -0800 (PST), George Herold > > <gherold@teachspin.com> wrote: > > > > >On Thursday, January 22, 2015 at 8:35:11 AM UTC-5, Alain Coste wrote:<snip>> > >I measured the diode drop on ~10 IRF820's in my part box and they were all within 1 mV of each other. (Not bad) (Don't touch with hands while measuring.) > > > > > >George H. > > > > That's impressive, less than 0.5 C. > > Yeah the diodes (transistors) I use for temp sensors have ~5-10 mV > of variation at room temp. > Hey, I've got a dewar of LN2 next to me.. > I'll dunk some in and see how well they track each other. > > later... > George H.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 Hey, what should I connect the gate to? (S or D or doesn't it matter?) I left it floating, which was kinda fun 'cause if I scuffed my shoe and touched the gate the channel would conduct. George H.> > > > > > > -- > > > > John Larkin Highland Technology, Inc > > picosecond timing precision measurement > > > > jlarkin att highlandtechnology dott com > > http://www.highlandtechnology.com
estimating junction temperature of a power mosfet
Started by ●January 21, 2015
Reply by ●January 23, 20152015-01-23
Reply by ●January 23, 20152015-01-23
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 1.0159What current did you use? Any self-heating?
Reply by ●January 23, 20152015-01-23
On Fri, 23 Jan 2015 07:54:21 -0800 (PST), George Herold <gherold@teachspin.com> wrote:>On Friday, January 23, 2015 at 8:31:21 AM UTC-5, George Herold wrote: >> On Thursday, January 22, 2015 at 3:18:56 PM UTC-5, John Larkin wrote: >> > On Thu, 22 Jan 2015 11:56:15 -0800 (PST), George Herold >> > <gherold@teachspin.com> wrote: >> > >> > >On Thursday, January 22, 2015 at 8:35:11 AM UTC-5, Alain Coste wrote: ><snip> >> > >I measured the diode drop on ~10 IRF820's in my part box and they were all within 1 mV of each other. (Not bad) (Don't touch with hands while measuring.) >> > > >> > >George H. >> > >> > That's impressive, less than 0.5 C. >> >> Yeah the diodes (transistors) I use for temp sensors have ~5-10 mV >> of variation at room temp. >> Hey, I've got a dewar of LN2 next to me.. >> I'll dunk some in and see how well they track each other. >> >> later... >> George H. > >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 1.0159That's amazing. Lakeshore won't like that. But I've found same-part same-manufacturer semiconductors to be very repeatable. Which sometimes lets one use measured specs that are way better than guaranteed specs.> >Hey, what should I connect the gate to? (S or D or doesn't it matter?)S or D but not floating. You don't want the channel to conduct and short out the substrate diode. You can bias a mosfet ON and disconnect the gate, and it may stay on for days.>I left it floating, which was kinda fun 'cause if I scuffed my shoe and touched the gate the channel would conduct.Reminds me of my fun-with-a-2N7000 experiments https://dl.dropboxusercontent.com/u/53724080/Parts/Fets/2N7000.jpg Gate leakage on a good 2N7000 is not many electrons per second. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●January 23, 20152015-01-23
On 01/23/2015 11:49 AM, John Larkin wrote:> On Fri, 23 Jan 2015 07:54:21 -0800 (PST), George Herold > <gherold@teachspin.com> wrote: > >> On Friday, January 23, 2015 at 8:31:21 AM UTC-5, George Herold wrote: >>> On Thursday, January 22, 2015 at 3:18:56 PM UTC-5, John Larkin wrote: >>>> On Thu, 22 Jan 2015 11:56:15 -0800 (PST), George Herold >>>> <gherold@teachspin.com> wrote: >>>> >>>>> On Thursday, January 22, 2015 at 8:35:11 AM UTC-5, Alain Coste wrote: >> <snip> >>>>> I measured the diode drop on ~10 IRF820's in my part box and they were all within 1 mV of each other. (Not bad) (Don't touch with hands while measuring.) >>>>> >>>>> George H. >>>> >>>> That's impressive, less than 0.5 C. >>> >>> Yeah the diodes (transistors) I use for temp sensors have ~5-10 mV >>> of variation at room temp. >>> Hey, I've got a dewar of LN2 next to me.. >>> I'll dunk some in and see how well they track each other. >>> >>> later... >>> George H. >> >> 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 > > That's amazing. Lakeshore won't like that. > > But I've found same-part same-manufacturer semiconductors to be very > repeatable. Which sometimes lets one use measured specs that are way > better than guaranteed specs. > >> >> Hey, what should I connect the gate to? (S or D or doesn't it matter?) > > S or D but not floating. You don't want the channel to conduct and > short out the substrate diode. You can bias a mosfet ON and disconnect > the gate, and it may stay on for days. > > >> I left it floating, which was kinda fun 'cause if I scuffed my shoe and touched the gate the channel would conduct. > > Reminds me of my fun-with-a-2N7000 experiments > > https://dl.dropboxusercontent.com/u/53724080/Parts/Fets/2N7000.jpg > > Gate leakage on a good 2N7000 is not many electrons per second.The unprotected 2N7002E parts are going away, though. Better buy a few reels while they last! Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●January 23, 20152015-01-23
On Fri, 23 Jan 2015 12:11:26 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 01/23/2015 11:49 AM, John Larkin wrote: >> On Fri, 23 Jan 2015 07:54:21 -0800 (PST), George Herold >> <gherold@teachspin.com> wrote: >> >>> On Friday, January 23, 2015 at 8:31:21 AM UTC-5, George Herold wrote: >>>> On Thursday, January 22, 2015 at 3:18:56 PM UTC-5, John Larkin wrote: >>>>> On Thu, 22 Jan 2015 11:56:15 -0800 (PST), George Herold >>>>> <gherold@teachspin.com> wrote: >>>>> >>>>>> On Thursday, January 22, 2015 at 8:35:11 AM UTC-5, Alain Coste wrote: >>> <snip> >>>>>> I measured the diode drop on ~10 IRF820's in my part box and they were all within 1 mV of each other. (Not bad) (Don't touch with hands while measuring.) >>>>>> >>>>>> George H. >>>>> >>>>> That's impressive, less than 0.5 C. >>>> >>>> Yeah the diodes (transistors) I use for temp sensors have ~5-10 mV >>>> of variation at room temp. >>>> Hey, I've got a dewar of LN2 next to me.. >>>> I'll dunk some in and see how well they track each other. >>>> >>>> later... >>>> George H. >>> >>> 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 >> >> That's amazing. Lakeshore won't like that. >> >> But I've found same-part same-manufacturer semiconductors to be very >> repeatable. Which sometimes lets one use measured specs that are way >> better than guaranteed specs. >> >>> >>> Hey, what should I connect the gate to? (S or D or doesn't it matter?) >> >> S or D but not floating. You don't want the channel to conduct and >> short out the substrate diode. You can bias a mosfet ON and disconnect >> the gate, and it may stay on for days. >> >> >>> I left it floating, which was kinda fun 'cause if I scuffed my shoe and touched the gate the channel would conduct. >> >> Reminds me of my fun-with-a-2N7000 experiments >> >> https://dl.dropboxusercontent.com/u/53724080/Parts/Fets/2N7000.jpg >> >> Gate leakage on a good 2N7000 is not many electrons per second. > >The unprotected 2N7002E parts are going away, though. Better buy a few >reels while they last! > >Cheers > >Phil HobbsI don't really care about gate leakage in a 2N7000, except for fun things. But I hope the gate protection zener is symmetrical, in case I have some old application where I pull the gate negative. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●January 23, 20152015-01-23
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.
Reply by ●January 23, 20152015-01-23
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. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●January 23, 20152015-01-23
On Friday, January 23, 2015 at 7:54:28 AM UTC-8, George Herold wrote:> On Friday, January 23, 2015 at 8:31:21 AM UTC-5, George Herold wrote: > > On Thursday, January 22, 2015 at 3:18:56 PM UTC-5, John Larkin wrote: > > > On Thu, 22 Jan 2015 11:56:15 -0800 (PST), George Herold > > > <gherold@teachspin.com> wrote: > > > > > > >On Thursday, January 22, 2015 at 8:35:11 AM UTC-5, Alain Coste wrote: > <snip> > > > >I measured the diode drop on ~10 IRF820's in my part box and they were all within 1 mV ...> > > That's impressive, less than 0.5 C.> > Hey, I've got a dewar of LN2 next to me.. > > I'll dunk some in and see how well they track each other.> (I only tested 4 FET's I had to solder wires on to go down into the dewar> V V > Room temp. 77K > 0.5500 1.0154 > 0.5504 1.0156 > 0.5508 1.0157 > 0.5509 1.0159So, it's up to plus/minus a part per thousand? That's encouraging, it translates to a fraction of a degree K (or C) . It's hard to be sure of 'room temp' matching, an oil or Fluorinert bath would be a prudent enhancement for that column. The 77K numbers are matched to 3 parts per ten thousand... Screw torque and bubbles in the heatsink goo are a bigger variable than the thermometric precision of the MOSFET junction. Torque on the screw fasteners and dust on the fan blades is a bigger uncertainty than the
Reply by ●January 23, 20152015-01-23
On Friday, January 23, 2015 at 6:13:38 PM UTC-5, whit3rd wrote:> On Friday, January 23, 2015 at 7:54:28 AM UTC-8, George Herold wrote: > > On Friday, January 23, 2015 at 8:31:21 AM UTC-5, George Herold wrote: > > > On Thursday, January 22, 2015 at 3:18:56 PM UTC-5, John Larkin wrote: > > > > On Thu, 22 Jan 2015 11:56:15 -0800 (PST), George Herold > > > > <gherold@teachspin.com> wrote: > > > > > > > > >On Thursday, January 22, 2015 at 8:35:11 AM UTC-5, Alain Coste wrote: > > <snip> > > > > >I measured the diode drop on ~10 IRF820's in my part box and they were all within 1 mV ... > > > > > That's impressive, less than 0.5 C. > > > > Hey, I've got a dewar of LN2 next to me.. > > > I'll dunk some in and see how well they track each other. > > > > (I only tested 4 FET's I had to solder wires on to go down into the dewar > > > V V > > Room temp. 77K > > 0.5500 1.0154 > > 0.5504 1.0156 > > 0.5508 1.0157 > > 0.5509 1.0159 > > So, it's up to plus/minus a part per thousand? That's encouraging, it translates > to a fraction of a degree K (or C) . It's hard to be sure of 'room temp' matching, an oil > or Fluorinert bath would be a prudent enhancement for that column. The 77K numbers > are matched to 3 parts per ten thousand... > > Screw torque and bubbles in the heatsink goo are a bigger variable than the > thermometric precision of the MOSFET junction. > > Torque on the screw fasteners and dust on the fan blades is a bigger uncertainty than > theYeah, the room temperature numbers were drifting all over the place. Fet's just lying on my lab bench, taped to a piece of paper. Just bolting 'em down to a single hunk of metal would help a lot. I'm not all that surprised by the decrease in variation with temperature. I've seen that before. George H. PS. I need to post an epoxy update, the glass beads failed miserably, Cracks everywhere, as you predicted.
Reply by ●January 24, 20152015-01-24
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?
