On Sat, 15 Feb 2014 11:33:13 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 2/15/2014 11:30 AM, krw@attt.bizz wrote: >> On Fri, 14 Feb 2014 21:01:06 -0800, josephkk >> <joseph_barrett@sbcglobal.net> wrote: >> >>> On Thu, 13 Feb 2014 18:45:32 -0800 (PST), George Herold >>> <gherold@teachspin.com> wrote: >>> >>>> On Thursday, February 13, 2014 7:43:58 PM UTC-5, Clifford Heath wrote: >>>>> On 14/02/14 02:51, Tim Wescott wrote: >>>>> >>>>>> On Thu, 13 Feb 2014 07:26:01 -0800, George Herold wrote: >>>>>>> Transistor as heater/ temp sensor. >>>>>> Using it as a temperature sensor would be complicated by the fact that, >>>>>> due to its recent service as a heater, it would be warmer than its >>>>>> surroundings. >>>>> >>>>> But you have time - measure the temperature curve after a heating pulse >>>>> and correlate that with a thermal model. Using a thermal model is the >>>>> only way of calculating how much of your heat has reached the target at >>>>> a given point in time, so you have to do it anyway. >>>>> >>>>> Clifford Heath. >>>> Yeah, Well I wasn't thinking as far ahead as curve fitting. I was hoping to be just able to wait ~5 time constants or so. I must admit I thought it might be fun to watch the heat leak out of the transistor. >>>> >>>> George H. >>> >>> Ya know George, the longer i think about this the less i like trying to >>> get a specific power for a specific duration with a transistor, and the >>> more i like SMD resistors, perhaps mounted "upside down". >>> >> How do you get pick-n-place to place them upside down? What sort of >> manufacturing process hoops do you have to jump through to do that? >> >> >Might have to re-reel them, but you don't need to. Indium-solder them >to the anodized Al, top down.Won't the solder short the resistors? ...but you have given me another idea. How expensive is indium solder?
Transitor as heater
Started by ●February 13, 2014
Reply by ●February 15, 20142014-02-15
Reply by ●February 15, 20142014-02-15
On Sat, 15 Feb 2014 11:33:13 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 2/15/2014 11:30 AM, krw@attt.bizz wrote: >> On Fri, 14 Feb 2014 21:01:06 -0800, josephkk >> <joseph_barrett@sbcglobal.net> wrote: >> >>> On Thu, 13 Feb 2014 18:45:32 -0800 (PST), George Herold >>> <gherold@teachspin.com> wrote: >>> >>>> On Thursday, February 13, 2014 7:43:58 PM UTC-5, Clifford Heath wrote: >>>>> On 14/02/14 02:51, Tim Wescott wrote: >>>>> >>>>>> On Thu, 13 Feb 2014 07:26:01 -0800, George Herold wrote: >>>>>>> Transistor as heater/ temp sensor. >>>>>> Using it as a temperature sensor would be complicated by the fact that, >>>>>> due to its recent service as a heater, it would be warmer than its >>>>>> surroundings. >>>>> >>>>> But you have time - measure the temperature curve after a heating pulse >>>>> and correlate that with a thermal model. Using a thermal model is the >>>>> only way of calculating how much of your heat has reached the target at >>>>> a given point in time, so you have to do it anyway. >>>>> >>>>> Clifford Heath. >>>> Yeah, Well I wasn't thinking as far ahead as curve fitting. I was hoping to be just able to wait ~5 time constants or so. I must admit I thought it might be fun to watch the heat leak out of the transistor. >>>> >>>> George H. >>> >>> Ya know George, the longer i think about this the less i like trying to >>> get a specific power for a specific duration with a transistor, and the >>> more i like SMD resistors, perhaps mounted "upside down". >>> >> How do you get pick-n-place to place them upside down? What sort of >> manufacturing process hoops do you have to jump through to do that? >> >> >Might have to re-reel them, but you don't need to. Indium-solder them >to the anodized Al, top down. > >Cheers > >Phil HobbsTo get the heat out, just mount them normally, soldered to biggish copper pours and then vias to copper on the opposite side of the board. Most of the heat flows out of the end caps. Or use some nice copperclad aluminum nitride. Inverted resistor mounting is useful at picosecond speeds. The reduction in inductance can be dramatic. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation
Reply by ●February 15, 20142014-02-15
On 2/15/2014 12:11 PM, krw@attt.bizz wrote:> On Sat, 15 Feb 2014 11:33:13 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 2/15/2014 11:30 AM, krw@attt.bizz wrote: >>> On Fri, 14 Feb 2014 21:01:06 -0800, josephkk >>> <joseph_barrett@sbcglobal.net> wrote: >>> >>>> On Thu, 13 Feb 2014 18:45:32 -0800 (PST), George Herold >>>> <gherold@teachspin.com> wrote: >>>> >>>>> On Thursday, February 13, 2014 7:43:58 PM UTC-5, Clifford Heath wrote: >>>>>> On 14/02/14 02:51, Tim Wescott wrote: >>>>>> >>>>>>> On Thu, 13 Feb 2014 07:26:01 -0800, George Herold wrote: >>>>>>>> Transistor as heater/ temp sensor. >>>>>>> Using it as a temperature sensor would be complicated by the fact that, >>>>>>> due to its recent service as a heater, it would be warmer than its >>>>>>> surroundings. >>>>>> >>>>>> But you have time - measure the temperature curve after a heating pulse >>>>>> and correlate that with a thermal model. Using a thermal model is the >>>>>> only way of calculating how much of your heat has reached the target at >>>>>> a given point in time, so you have to do it anyway. >>>>>> >>>>>> Clifford Heath. >>>>> Yeah, Well I wasn't thinking as far ahead as curve fitting. I was hoping to be just able to wait ~5 time constants or so. I must admit I thought it might be fun to watch the heat leak out of the transistor. >>>>> >>>>> George H. >>>> >>>> Ya know George, the longer i think about this the less i like trying to >>>> get a specific power for a specific duration with a transistor, and the >>>> more i like SMD resistors, perhaps mounted "upside down". >>>> >>> How do you get pick-n-place to place them upside down? What sort of >>> manufacturing process hoops do you have to jump through to do that? >>> >>> >> Might have to re-reel them, but you don't need to. Indium-solder them >> to the anodized Al, top down. > > Won't the solder short the resistors?Not unless you let it bridge between the pads.> > ...but you have given me another idea. How expensive is indium > solder?Expensive. 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 ●February 15, 20142014-02-15
On 2/15/2014 12:21 PM, John Larkin wrote:> On Sat, 15 Feb 2014 11:33:13 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 2/15/2014 11:30 AM, krw@attt.bizz wrote: >>> On Fri, 14 Feb 2014 21:01:06 -0800, josephkk >>> <joseph_barrett@sbcglobal.net> wrote: >>> >>>> On Thu, 13 Feb 2014 18:45:32 -0800 (PST), George Herold >>>> <gherold@teachspin.com> wrote: >>>> >>>>> On Thursday, February 13, 2014 7:43:58 PM UTC-5, Clifford Heath wrote: >>>>>> On 14/02/14 02:51, Tim Wescott wrote: >>>>>> >>>>>>> On Thu, 13 Feb 2014 07:26:01 -0800, George Herold wrote: >>>>>>>> Transistor as heater/ temp sensor. >>>>>>> Using it as a temperature sensor would be complicated by the fact that, >>>>>>> due to its recent service as a heater, it would be warmer than its >>>>>>> surroundings. >>>>>> >>>>>> But you have time - measure the temperature curve after a heating pulse >>>>>> and correlate that with a thermal model. Using a thermal model is the >>>>>> only way of calculating how much of your heat has reached the target at >>>>>> a given point in time, so you have to do it anyway. >>>>>> >>>>>> Clifford Heath. >>>>> Yeah, Well I wasn't thinking as far ahead as curve fitting. I was hoping to be just able to wait ~5 time constants or so. I must admit I thought it might be fun to watch the heat leak out of the transistor. >>>>> >>>>> George H. >>>> >>>> Ya know George, the longer i think about this the less i like trying to >>>> get a specific power for a specific duration with a transistor, and the >>>> more i like SMD resistors, perhaps mounted "upside down". >>>> >>> How do you get pick-n-place to place them upside down? What sort of >>> manufacturing process hoops do you have to jump through to do that? >>> >>> >> Might have to re-reel them, but you don't need to. Indium-solder them >> to the anodized Al, top down. >> >> Cheers >> >> Phil Hobbs > > To get the heat out, just mount them normally, soldered to biggish copper pours > and then vias to copper on the opposite side of the board. Most of the heat > flows out of the end caps.Tends to be slow, though. I'm a big fan of maximizing bandwidth in thermal systems.> > Or use some nice copperclad aluminum nitride. > > Inverted resistor mounting is useful at picosecond speeds. The reduction in > inductance can be dramatic.Interesting idea, thanks. 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 On 2/15/2014 12:21 PM, John Larkin wrote: > On Sat, 15 Feb 2014 11:33:13 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 2/15/2014 11:30 AM, krw@attt.bizz wrote: >>> On Fri, 14 Feb 2014 21:01:06 -0800, josephkk >>> <joseph_barrett@sbcglobal.net> wrote: >>> >>>> On Thu, 13 Feb 2014 18:45:32 -0800 (PST), George Herold >>>> <gherold@teachspin.com> wrote: >>>> >>>>> On Thursday, February 13, 2014 7:43:58 PM UTC-5, Clifford Heath wrote: >>>>>> On 14/02/14 02:51, Tim Wescott wrote: >>>>>> >>>>>>> On Thu, 13 Feb 2014 07:26:01 -0800, George Herold wrote: >>>>>>>> Transistor as heater/ temp sensor. >>>>>>> Using it as a temperature sensor would be complicated by the fact that, >>>>>>> due to its recent service as a heater, it would be warmer than its >>>>>>> surroundings. >>>>>> >>>>>> But you have time - measure the temperature curve after a heating pulse >>>>>> and correlate that with a thermal model. Using a thermal model is the >>>>>> only way of calculating how much of your heat has reached the target at >>>>>> a given point in time, so you have to do it anyway. >>>>>> >>>>>> Clifford Heath. >>>>> Yeah, Well I wasn't thinking as far ahead as curve fitting. I was hoping to be just able to wait ~5 time constants or so. I must admit I thought it might be fun to watch the heat leak out of the transistor. >>>>> >>>>> George H. >>>> >>>> Ya know George, the longer i think about this the less i like trying to >>>> get a specific power for a specific duration with a transistor, and the >>>> more i like SMD resistors, perhaps mounted "upside down". >>>> >>> How do you get pick-n-place to place them upside down? What sort of >>> manufacturing process hoops do you have to jump through to do that? >>> >>> >> Might have to re-reel them, but you don't need to. Indium-solder them >> to the anodized Al, top down. >> >> Cheers >> >> Phil Hobbs > > To get the heat out, just mount them normally, soldered to biggish copper pours > and then vias to copper on the opposite side of the board. Most of the heat > flows out of the end caps. > > Or use some nice copperclad aluminum nitride. > > Inverted resistor mounting is useful at picosecond speeds. The reduction in > inductance can be dramatic. > > -- 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 ●February 15, 20142014-02-15
On Sat, 15 Feb 2014 12:35:47 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 2/15/2014 12:11 PM, krw@attt.bizz wrote: >> On Sat, 15 Feb 2014 11:33:13 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 2/15/2014 11:30 AM, krw@attt.bizz wrote: >>>> On Fri, 14 Feb 2014 21:01:06 -0800, josephkk >>>> <joseph_barrett@sbcglobal.net> wrote: >>>> >>>>> On Thu, 13 Feb 2014 18:45:32 -0800 (PST), George Herold >>>>> <gherold@teachspin.com> wrote: >>>>> >>>>>> On Thursday, February 13, 2014 7:43:58 PM UTC-5, Clifford Heath wrote: >>>>>>> On 14/02/14 02:51, Tim Wescott wrote: >>>>>>> >>>>>>>> On Thu, 13 Feb 2014 07:26:01 -0800, George Herold wrote: >>>>>>>>> Transistor as heater/ temp sensor. >>>>>>>> Using it as a temperature sensor would be complicated by the fact that, >>>>>>>> due to its recent service as a heater, it would be warmer than its >>>>>>>> surroundings. >>>>>>> >>>>>>> But you have time - measure the temperature curve after a heating pulse >>>>>>> and correlate that with a thermal model. Using a thermal model is the >>>>>>> only way of calculating how much of your heat has reached the target at >>>>>>> a given point in time, so you have to do it anyway. >>>>>>> >>>>>>> Clifford Heath. >>>>>> Yeah, Well I wasn't thinking as far ahead as curve fitting. I was hoping to be just able to wait ~5 time constants or so. I must admit I thought it might be fun to watch the heat leak out of the transistor. >>>>>> >>>>>> George H. >>>>> >>>>> Ya know George, the longer i think about this the less i like trying to >>>>> get a specific power for a specific duration with a transistor, and the >>>>> more i like SMD resistors, perhaps mounted "upside down". >>>>> >>>> How do you get pick-n-place to place them upside down? What sort of >>>> manufacturing process hoops do you have to jump through to do that? >>>> >>>> >>> Might have to re-reel them, but you don't need to. Indium-solder them >>> to the anodized Al, top down. >> >> Won't the solder short the resistors? > >Not unless you let it bridge between the pads. > >> >> ...but you have given me another idea. How expensive is indium >> solder? > >Expensive.Yeah, $100 for 3' x .030" wire. It's a bit much for production but still interesting as a lab toy. http://buy.solder.com/Solder-Wire/C61_1/
Reply by ●February 15, 20142014-02-15
On Sat, 15 Feb 2014 12:58:35 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 2/15/2014 12:21 PM, John Larkin wrote: >> On Sat, 15 Feb 2014 11:33:13 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 2/15/2014 11:30 AM, krw@attt.bizz wrote: >>>> On Fri, 14 Feb 2014 21:01:06 -0800, josephkk >>>> <joseph_barrett@sbcglobal.net> wrote: >>>> >>>>> On Thu, 13 Feb 2014 18:45:32 -0800 (PST), George Herold >>>>> <gherold@teachspin.com> wrote: >>>>> >>>>>> On Thursday, February 13, 2014 7:43:58 PM UTC-5, Clifford Heath wrote: >>>>>>> On 14/02/14 02:51, Tim Wescott wrote: >>>>>>> >>>>>>>> On Thu, 13 Feb 2014 07:26:01 -0800, George Herold wrote: >>>>>>>>> Transistor as heater/ temp sensor. >>>>>>>> Using it as a temperature sensor would be complicated by the fact that, >>>>>>>> due to its recent service as a heater, it would be warmer than its >>>>>>>> surroundings. >>>>>>> >>>>>>> But you have time - measure the temperature curve after a heating pulse >>>>>>> and correlate that with a thermal model. Using a thermal model is the >>>>>>> only way of calculating how much of your heat has reached the target at >>>>>>> a given point in time, so you have to do it anyway. >>>>>>> >>>>>>> Clifford Heath. >>>>>> Yeah, Well I wasn't thinking as far ahead as curve fitting. I was hoping to be just able to wait ~5 time constants or so. I must admit I thought it might be fun to watch the heat leak out of the transistor. >>>>>> >>>>>> George H. >>>>> >>>>> Ya know George, the longer i think about this the less i like trying to >>>>> get a specific power for a specific duration with a transistor, and the >>>>> more i like SMD resistors, perhaps mounted "upside down". >>>>> >>>> How do you get pick-n-place to place them upside down? What sort of >>>> manufacturing process hoops do you have to jump through to do that? >>>> >>>> >>> Might have to re-reel them, but you don't need to. Indium-solder them >>> to the anodized Al, top down. >>> >>> Cheers >>> >>> Phil Hobbs >> >> To get the heat out, just mount them normally, soldered to biggish copper pours >> and then vias to copper on the opposite side of the board. Most of the heat >> flows out of the end caps. > >Tends to be slow, though. I'm a big fan of maximizing bandwidth in >thermal systems.I don't think flipping surface-mount resistors will reduce tau much, unless you put some thermal filler between the resistor and the PCB. The air gap there will have a much higher thermal resistance than the path through the alumina. For a huge power-to-mass ratio, use AlN or BeO RF terminator resistors. Maybe George could use a flange-mount terminator as his heater.> >> >> Or use some nice copperclad aluminum nitride. >> >> Inverted resistor mounting is useful at picosecond speeds. The reduction in >> inductance can be dramatic. > >Interesting idea, thanks.Here are some waveforms, 0805 inserted in a gap in a CPW trace: https://dl.dropboxusercontent.com/u/53724080/Parts/Resistors/0805_res_fix.JPG https://dl.dropboxusercontent.com/u/53724080/Parts/Resistors/0805_normal.JPG https://dl.dropboxusercontent.com/u/53724080/Parts/Resistors/0805_flipped.JPG The bump at cm 3.5 is the resistor's inductance. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation
Reply by ●February 15, 20142014-02-15
On 2/15/2014 1:14 PM, John Larkin wrote:> On Sat, 15 Feb 2014 12:58:35 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 2/15/2014 12:21 PM, John Larkin wrote: >>> On Sat, 15 Feb 2014 11:33:13 -0500, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> On 2/15/2014 11:30 AM, krw@attt.bizz wrote: >>>>> On Fri, 14 Feb 2014 21:01:06 -0800, josephkk >>>>> <joseph_barrett@sbcglobal.net> wrote: >>>>> >>>>>> On Thu, 13 Feb 2014 18:45:32 -0800 (PST), George Herold >>>>>> <gherold@teachspin.com> wrote: >>>>>> >>>>>>> On Thursday, February 13, 2014 7:43:58 PM UTC-5, Clifford Heath wrote: >>>>>>>> On 14/02/14 02:51, Tim Wescott wrote: >>>>>>>> >>>>>>>>> On Thu, 13 Feb 2014 07:26:01 -0800, George Herold wrote: >>>>>>>>>> Transistor as heater/ temp sensor. >>>>>>>>> Using it as a temperature sensor would be complicated by the fact that, >>>>>>>>> due to its recent service as a heater, it would be warmer than its >>>>>>>>> surroundings. >>>>>>>> >>>>>>>> But you have time - measure the temperature curve after a heating pulse >>>>>>>> and correlate that with a thermal model. Using a thermal model is the >>>>>>>> only way of calculating how much of your heat has reached the target at >>>>>>>> a given point in time, so you have to do it anyway. >>>>>>>> >>>>>>>> Clifford Heath. >>>>>>> Yeah, Well I wasn't thinking as far ahead as curve fitting. I was hoping to be just able to wait ~5 time constants or so. I must admit I thought it might be fun to watch the heat leak out of the transistor. >>>>>>> >>>>>>> George H. >>>>>> >>>>>> Ya know George, the longer i think about this the less i like trying to >>>>>> get a specific power for a specific duration with a transistor, and the >>>>>> more i like SMD resistors, perhaps mounted "upside down". >>>>>> >>>>> How do you get pick-n-place to place them upside down? What sort of >>>>> manufacturing process hoops do you have to jump through to do that? >>>>> >>>>> >>>> Might have to re-reel them, but you don't need to. Indium-solder them >>>> to the anodized Al, top down. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> To get the heat out, just mount them normally, soldered to biggish copper pours >>> and then vias to copper on the opposite side of the board. Most of the heat >>> flows out of the end caps. >> >> Tends to be slow, though. I'm a big fan of maximizing bandwidth in >> thermal systems. > > I don't think flipping surface-mount resistors will reduce tau much, unless you > put some thermal filler between the resistor and the PCB. The air gap there will > have a much higher thermal resistance than the path through the alumina. > > For a huge power-to-mass ratio, use AlN or BeO RF terminator resistors. Maybe > George could use a flange-mount terminator as his heater. >I'm talking about indium-soldering the tops of the caps to the back of the anodized Al. The thermal diffusivity of plastic is roughly 1000 times slower than aluminum.> >> >>> >>> Or use some nice copperclad aluminum nitride. >>> >>> Inverted resistor mounting is useful at picosecond speeds. The reduction in >>> inductance can be dramatic. >> >> Interesting idea, thanks. > > Here are some waveforms, 0805 inserted in a gap in a CPW trace: > > https://dl.dropboxusercontent.com/u/53724080/Parts/Resistors/0805_res_fix.JPG > > https://dl.dropboxusercontent.com/u/53724080/Parts/Resistors/0805_normal.JPG > > https://dl.dropboxusercontent.com/u/53724080/Parts/Resistors/0805_flipped.JPG > > The bump at cm 3.5 is the resistor's inductance.Looks like about a factor of two improvement. Nice. 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 ●February 15, 20142014-02-15
On Saturday, February 15, 2014 8:21:58 AM UTC-8, Phil Hobbs wrote:> On 2/15/2014 4:15 AM, stratus46 wrote:<snip>>=20 > > I needed to use a transistor as a log/antilog element but ambient >=20 > > temperature is part of the equation. I used a matched quad transistor >=20 > > array from Analog Devices. One transistor is the temp sensor, 2 are >=20 > > used as heaters and the fourth transistor actually does the 'work'. >=20 > > >=20 > > The control opamp was from a note by Jim Williams and it works very >=20 > > well. I had to use 15 ohm emitter resistors on the heaters to limit >=20 > > the current to a safe value when cold. Watching the emitter current >=20 > > of the heaters and the temp sense output while placing your finger on >=20 > > the 14 pin DIP case shows heater current going up while you touch and >=20 > > falling back down when you let go. The temp output shows a constant >=20 > > 462mV which corresponds to 69C internally. >=20 >=20 >=20 > I've used that trick quite often, since seeing it in an app note back=20 >=20 > around 1990, when the MAT-04 first came out. Works better in the=20 >=20 > ceramic DIP package than the SMT ones, but they don't make those anymore==20>=20 > of course. >=20 >=20 >=20 > Cheers >=20 >=20 >=20 > Phil Hobbs >=20 >=20 >=20 > --=20 >=20 > Dr Philip C D Hobbs >=20 > Principal Consultant >=20 > ElectroOptical Innovations LLC >=20 > Optics, Electro-optics, Photonics, Analog Electronics >=20 >=20 >=20 > 160 North State Road #203 >=20 > Briarcliff Manor NY 10510 >=20 >=20 >=20 > hobbs at electrooptical dot net >=20 > http://electrooptical.netMAT14 is SOIC and available. G=B2
Reply by ●February 16, 20142014-02-16
On 2/15/2014 6:03 PM, stratus46 wrote:> On Saturday, February 15, 2014 8:21:58 AM UTC-8, Phil Hobbs wrote: >> On 2/15/2014 4:15 AM, stratus46 wrote: > <snip> >>> I needed to use a transistor as a log/antilog element but >>> ambient temperature is part of the equation. I used a matched >>> quad transistor array from Analog Devices. One transistor is the >>> temp sensor, 2 are used as heaters and the fourth transistor >>> actually does the 'work'. > >>> The control opamp was from a note by Jim Williams and it works >>> very well. I had to use 15 ohm emitter resistors on the heaters >>> to limit the current to a safe value when cold. Watching the >>> emitter current of the heaters and the temp sense output while >>> placing your finger on the 14 pin DIP case shows heater current >>> going up while you touch and falling back down when you let go. >>> The temp output shows a constant 462mV which corresponds to 69C >>> internally. >> I've used that trick quite often, since seeing it in an app note >> back around 1990, when the MAT-04 first came out. Works better in >> the ceramic DIP package than the SMT ones, but they don't make >> those anymore of course. > > MAT14 is SOIC and available.Sure, I know about that, but (a) they gutted the datasheet, meaning that they gutted the testing, and (b) they don't come in CERDIP. CERDIP packages have Kovar leads, which have much lower thermal conductance. (They also have worse thermocouple offsets, so you have to be careful there, or at least you did when you could still get them.) Cheers Phil Hobbs (*) I wrote a paper long ago that included this trick: http://electrooptical.net/www/canceller/noisecan.pdf -- 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 ●February 17, 20142014-02-17
On Friday, February 14, 2014 10:57:39 PM UTC-5, josephkk wrote:> On Thu, 13 Feb 2014 18:45:32 -0800 (PST), George Herold >=20 > <gherold@teachspin.com> wrote: >=20 >=20 >=20 > >On Thursday, February 13, 2014 7:43:58 PM UTC-5, Clifford Heath wrote: >=20 > >> On 14/02/14 02:51, Tim Wescott wrote: >=20 > >>=20 >=20 > >> > On Thu, 13 Feb 2014 07:26:01 -0800, George Herold wrote: > >> >> Transistor as heater/ temp sensor. > >> > Using it as a temperature sensor would be complicated by the fact th=at,> >> > due to its recent service as a heater, it would be warmer than its > >> > surroundings. > >>=20 >=20 > >> But you have time - measure the temperature curve after a heating puls=e=20> >> and correlate that with a thermal model. Using a thermal model is the==20> >> only way of calculating how much of your heat has reached the target a=t=20> >> a given point in time, so you have to do it anyway. > >>=20 > >> Clifford Heath.=20 > >Yeah, Well I wasn't thinking as far ahead as curve fitting. I was hopi=ng to be just able to wait ~5 time constants or so. I must admit I thought= it might be fun to watch the heat leak out of the transistor. =20> >=20 > >George H.=20 >=20 >=20 > Ya know George, the longer i think about this the less i like trying to==20> get a specific power for a specific duration with a transistor, and the > more i like SMD resistors, perhaps mounted "upside down".Hmm OK why is that Joseph? I think I'm going to have to run four wires dow= n to do either ther resistor or transistor as heater. (measure the voltage= and current.) I guess there is some beta current error.. I've ordered a b= unch of pnp medium power transistors. Beta's in the ~200 range but that dr= ops at low temperature. But the SOT89 packs look great...=20 they weight less than 100 mg! I guess I should look at some FETS...=20 George H.>=20 >=20 >=20 > ?-)
