Forums

Transitor as heater

Started by George Herold February 13, 2014
On Fri, 14 Feb 2014 06:18:56 -0800 (PST), George Herold
<gherold@teachspin.com> wrote:

>(Well I didn't mention to other reason which is that you tend to write *a lot* :^)
If I had more time, I would have made it shorter. (Mark Twain). I also like to think that quantity is a tolerable substitute for quality.
><snip rest of IR led stuff>
My LED idea isn't going to work. LED's belch IR in the near-IR region. For heating, you want far-IR, which LED's will not do. You can probably get a rough idea of the thermal characteristics from a near-IR test, but if there is anything in the system that is sensitive to wavelength, accuracy will suffer severely.
>That's the idea anyway. I haven't tried it yet and perhaps it >will crash and burn because of somethng I've forgotten.
That's why I like to build prototypes and concept models. The problem areas are usually identifiable by fire, smoke, sparks, explosions, etc. I'm out of my depth on this one. To avoid further embarrassment, I'll just lurk and defer to those that know what they're doing. Good luck. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
"Jeff Liebermann" <jeffl@cruzio.com> wrote in message 
news:92rsf9phhnqsie6ab1ap1o3slhr45l554h@4ax.com...
> My LED idea isn't going to work. LED's belch IR in the near-IR > region. For heating, you want far-IR, which LED's will not do. You > can probably get a rough idea of the thermal characteristics from a > near-IR test, but if there is anything in the system that is sensitive > to wavelength, accuracy will suffer severely.
Heating, yes; sensing, no (unless you get one of those special metal and glass package ones that's miliwatts and kilodollars..). I have here a single-AA flashlight that I made, fitted with a high power LED, which runs about 1W at 67% electrical efficiency. The emitter itself is going to be around 10%, or overall, about 60mW light output, within the 350-700nm band. Holding it point blank to my lip and turning it on and off, it feels about like warm breath, except I'm holding my breath, and it's switch operated. Absorption is absorption. The same goes for radiation below the blackbody peak, of course; induction heating doesn't have to resonate with the work to make it glow. (Which is, in effect, a very efficient, extraordinarily noisy, wideband upconverter. :) ) Tim -- Seven Transistor Labs Electrical Engineering Consultation Website: http://seventransistorlabs.com
On 2/14/2014 5:23 PM, Tim Williams wrote:
> "Jeff Liebermann" <jeffl@cruzio.com> wrote in message > news:92rsf9phhnqsie6ab1ap1o3slhr45l554h@4ax.com... >> My LED idea isn't going to work. LED's belch IR in the near-IR >> region. For heating, you want far-IR, which LED's will not do. You >> can probably get a rough idea of the thermal characteristics from a >> near-IR test, but if there is anything in the system that is sensitive >> to wavelength, accuracy will suffer severely. > > Heating, yes; sensing, no (unless you get one of those special metal and > glass package ones that's miliwatts and kilodollars..). > > I have here a single-AA flashlight that I made, fitted with a high power > LED, which runs about 1W at 67% electrical efficiency. The emitter itself > is going to be around 10%, or overall, about 60mW light output, within the > 350-700nm band. Holding it point blank to my lip and turning it on and > off, it feels about like warm breath, except I'm holding my breath, and > it's switch operated. Absorption is absorption. > > The same goes for radiation below the blackbody peak, of course; induction > heating doesn't have to resonate with the work to make it glow. (Which > is, in effect, a very efficient, extraordinarily noisy, wideband > upconverter. :) ) > > Tim >
'Tain't quite as bad as that. Blacken one side of a piece of copper foil with a torch. Heat it from the back with a fibre-coupled 850-nm laser, and put the sample on the front (shiny) side. 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 Friday, February 14, 2014 6:16:50 PM UTC-5, Phil Hobbs wrote:
> On 2/14/2014 5:23 PM, Tim Williams wrote: > > > "Jeff Liebermann" <jeffl@cruzio.com> wrote in message > > > news:92rsf9phhnqsie6ab1ap1o3slhr45l554h@4ax.com... > > >> My LED idea isn't going to work. LED's belch IR in the near-IR > > >> region. For heating, you want far-IR, which LED's will not do. You > > >> can probably get a rough idea of the thermal characteristics from a > > >> near-IR test, but if there is anything in the system that is sensitive > > >> to wavelength, accuracy will suffer severely. > > > > > > Heating, yes; sensing, no (unless you get one of those special metal and > > > glass package ones that's miliwatts and kilodollars..). > > > > > > I have here a single-AA flashlight that I made, fitted with a high power > > > LED, which runs about 1W at 67% electrical efficiency. The emitter itself > > > is going to be around 10%, or overall, about 60mW light output, within the > > > 350-700nm band. Holding it point blank to my lip and turning it on and > > > off, it feels about like warm breath, except I'm holding my breath, and > > > it's switch operated. Absorption is absorption. > > > > > > The same goes for radiation below the blackbody peak, of course; induction > > > heating doesn't have to resonate with the work to make it glow. (Which > > > is, in effect, a very efficient, extraordinarily noisy, wideband > > > upconverter. :) ) > > > > > > Tim > > > > > > > 'Tain't quite as bad as that. Blacken one side of a piece of copper > foil with a torch. Heat it from the back with a fibre-coupled 850-nm > laser, and put the sample on the front (shiny) side.
My problem with an optical power measurement, is that beyond the ~10% error level it get's hard/expensive. How good is the blackened bit of copper? George H.
> > 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 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: >>=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 =
that,
>> > due to its recent service as a heater, it would be warmer than its >> > surroundings. >>=20 >> But you have time - measure the temperature curve after a heating =
pulse=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 =
at=20
>> a given point in time, so you have to do it anyway. >>=20 >> 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.=20
> >George H.=20
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". ?-)
On Thursday, February 13, 2014 7:26:01 AM UTC-8, George Herold wrote:
> Transistor as heater/ temp sensor. =20 >=20 > So in looking for a small heater one idea is to use a transistor as heate=
r. =20
>=20 > And to take the idea one step further to use the same transistor (sequent=
ially)
>=20 > As first a heater then a temp sensor. =20 >=20 > So the first question is then how to use it as a heater. I was thinking =
of controlling the current=20
>=20 > At some fixed voltage.. something like this, >=20 >=20 >=20 > https://www.dropbox.com/s/plcgg2rgnh0byt7/Tran-heat.JPG >=20 >=20 >=20 > But other ideas would be welcome. One semi-crazy idea, I'm using the tra=
nsistor as a temp sensor with the c-b shorted. (diode connected transistor= .) Could I just push a bunch more current through it for a heater. =20
>=20 >=20 >=20 > The second problem I see with the heater idea is how to do the switching =
from heater to temp sensor. Do I use relays or analog switches? =20
>=20 > (I'm off to look into anaolg switches.) >=20 >=20 >=20 > Thanks again, >=20 > George H.
I needed to use a transistor as a log/antilog element but ambient temperatu= re is part of the equation. I used a matched quad transistor array from Ana= log Devices. One transistor is the temp sensor, 2 are used as heaters and t= he fourth transistor actually does the 'work'.=20 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 th= e 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 interna= lly. G=B2
On 2/14/2014 9:02 PM, George Herold wrote:
> On Friday, February 14, 2014 6:16:50 PM UTC-5, Phil Hobbs wrote: >> On 2/14/2014 5:23 PM, Tim Williams wrote: >> >>> "Jeff Liebermann" <jeffl@cruzio.com> wrote in message >> >>> news:92rsf9phhnqsie6ab1ap1o3slhr45l554h@4ax.com... >> >>>> My LED idea isn't going to work. LED's belch IR in the >>>> near-IR region. For heating, you want far-IR, which LED's will >>>> not do. You can probably get a rough idea of the thermal >>>> characteristics from a near-IR test, but if there is anything >>>> in the system that is sensitive to wavelength, accuracy will >>>> suffer severely. >>> >>> Heating, yes; sensing, no (unless you get one of those special >>> metal and glass package ones that's miliwatts and >>> kilodollars..). >>> >>> I have here a single-AA flashlight that I made, fitted with a >>> high power LED, which runs about 1W at 67% electrical >>> efficiency. The emitter itself is going to be around 10%, or >>> overall, about 60mW light output, within the 350-700nm band. >>> Holding it point blank to my lip and turning it on and off, it >>> feels about like warm breath, except I'm holding my breath, and >>> it's switch operated. Absorption is absorption. >>> >>> The same goes for radiation below the blackbody peak, of course; >>> induction heating doesn't have to resonate with the work to make >>> it glow. (Which is, in effect, a very efficient, extraordinarily >>> noisy, wideband upconverter. :) ) >> >>> >> >>> Tim >> >>> >> >> >> >> 'Tain't quite as bad as that. Blacken one side of a piece of >> copper foil with a torch. Heat it from the back with a >> fibre-coupled 850-nm laser, and put the sample on the front (shiny) >> side. > > My problem with an optical power measurement, is that beyond the ~10% > error level it get's hard/expensive. How good is the blackened bit of > copper? >
It can be very good indeed, if e.g. you fold it back on itself and just have the fibre come through a small hole. Multiple bounces off black surfaces are the ticket. But for your use, probably a bit of anodized aluminum, with sample on one side and a Kapton flex on the back. I'd try putting the component side next to the aluminum, with the resistors and RTDs in good contact with the back. A blob of indium solder on the top of their pads will squash down very nicely on the Al, and will survive temperature cycling (as long as you don't melt it on the high-T excursion). The anodizing will give you nice durable insulation with low thermal resistance. Thin copper traces on flex are the lowest thermal conductance solution that I know of. You can make them serpentine if you like, to gain about a factor of 3. 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 4:15 AM, stratus46 wrote:
> On Thursday, February 13, 2014 7:26:01 AM UTC-8, George Herold > wrote: >> Transistor as heater/ temp sensor. >> >> So in looking for a small heater one idea is to use a transistor as >> heater. >> >> And to take the idea one step further to use the same transistor >> (sequentially) >> >> As first a heater then a temp sensor. >> >> So the first question is then how to use it as a heater. I was >> thinking of controlling the current >> >> At some fixed voltage.. something like this, >> >> >> >> https://www.dropbox.com/s/plcgg2rgnh0byt7/Tran-heat.JPG >> >> >> >> But other ideas would be welcome. One semi-crazy idea, I'm using >> the transistor as a temp sensor with the c-b shorted. (diode >> connected transistor.) Could I just push a bunch more current >> through it for a heater. >> >> >> >> The second problem I see with the heater idea is how to do the >> switching from heater to temp sensor. Do I use relays or analog >> switches? >> >> (I'm off to look into anaolg switches.) >> >> >> >> Thanks again, >> >> George H. > > 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. 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 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?
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 -- 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