Forums

Zenering a big transistor

Started by George Herold June 26, 2017
On Monday, June 26, 2017 at 5:21:53 PM UTC-4, dagmarg...@yahoo.com wrote:
> On Monday, June 26, 2017 at 1:15:44 PM UTC-4, John Larkin wrote: > > On Mon, 26 Jun 2017 10:04:35 -0700 (PDT), dagmargoodboat@yahoo.com > > wrote: > > > > >On Monday, June 26, 2017 at 12:59:50 PM UTC-4, dagmarg...@yahoo.com wrote: > > >> On Monday, June 26, 2017 at 11:51:45 AM UTC-4, George Herold wrote: > > >> > I'm using a TIP31C (pnp in to-220 pac) as a temp sensor (diode connected) > > >> > There's a couple of depletion fets in series as current limiters. (LND150) > > >> > The b-e junction starts to zener at ~30 V (only two tested so far). > > >> > So I've got ~1.5 mA flowing at 30 V. Is this going to damage the junction? > > >> > Will it take time? I'm going to measure forward voltage again after > > >> > zenering for 15 minutes. Should I measure something else too? > > >> > > > >> > TIA > > >> > > > >> > George H. > > >> > > >> Why not just protect your TIP31C from zenering? A few diodes would do it. > > >> > > > > > >e.g., > > > | > > > +----. > > > | | > > >TIP31C |<' --- > > > .---| ^ D1 > > > | |\ | > > > | | | > > > '-----+----' > > > | > > > | > > > > > >Add a zener in series with D1 if you need to stand off some reverse voltage. > > > > > >Cheers, > > >James Arthur > > > > Or use the c-b junction instead. > > That loses the transistor action, degrading its temperature-sensing > performance. > > Cheers, > James Arthur
So I let the transistor zener through the night. In the morning the forward voltage had changed by about 2 mV ~ 1 K. I'm going to recommend an LED in parallel, then when there is a reverse voltage the LED will light! George H.
On Tuesday, June 27, 2017 at 10:02:22 AM UTC-4, John Larkin wrote:
> On Mon, 26 Jun 2017 18:02:21 -0700 (PDT), dagmargoodboat@yahoo.com > wrote: > > >On Monday, June 26, 2017 at 8:17:45 PM UTC-4, dagmarg...@yahoo.com wrote: > >> On Monday, June 26, 2017 at 5:33:47 PM UTC-4, John Larkin wrote: > >> > On Mon, 26 Jun 2017 14:21:43 -0700 (PDT), dagmargoodboat@yahoo.com > >> > wrote: > >> > > >> > >On Monday, June 26, 2017 at 1:15:44 PM UTC-4, John Larkin wrote: > >> > >> On Mon, 26 Jun 2017 10:04:35 -0700 (PDT), dagmargoodboat@yahoo.com > >> > >> wrote: > >> > >> > >> > >> >On Monday, June 26, 2017 at 12:59:50 PM UTC-4, dagmarg...@yahoo.com wrote: > >> > >> >> On Monday, June 26, 2017 at 11:51:45 AM UTC-4, George Herold wrote: > >> > >> >> > I'm using a TIP31C (pnp in to-220 pac) as a temp sensor (diode connected) > >> > >> >> > There's a couple of depletion fets in series as current limiters. (LND150) > >> > >> >> > The b-e junction starts to zener at ~30 V (only two tested so far). > >> > >> >> > So I've got ~1.5 mA flowing at 30 V. Is this going to damage the junction? > >> > >> >> > Will it take time? I'm going to measure forward voltage again after > >> > >> >> > zenering for 15 minutes. Should I measure something else too? > >> > >> >> > > >> > >> >> > TIA > >> > >> >> > > >> > >> >> > George H. > >> > >> >> > >> > >> >> Why not just protect your TIP31C from zenering? A few diodes would do it. > >> > >> >> > >> > >> > > >> > >> >e.g., > >> > >> > | > >> > >> > +----. > >> > >> > | | > >> > >> >TIP31C |<' --- > >> > >> > .---| ^ D1 > >> > >> > | |\ | > >> > >> > | | | > >> > >> > '-----+----' > >> > >> > | > >> > >> > | > >> > >> > > >> > >> >Add a zener in series with D1 if you need to stand off some reverse voltage. > >> > >> > > >> > >> >Cheers, > >> > >> >James Arthur > >> > >> > >> > >> Or use the c-b junction instead. > >> > > > >> > >That loses the transistor action, degrading its temperature-sensing > >> > >performance. > >> > > > >> > >Cheers, > >> > >James Arthur > >> > > >> > Think so? It's still a diode with a roughly -2 mV/K tempco. > >> > >> I read that ages ago, in an early article about using Motorola transistors > >> specifically spec'd as temperature sensors IIRC. (It's amazing I can > >> remember that. Still have the article somewhere, I'm sure.) > >> > >> > No transistor will ever be a super-accurate temp sensor. > >> > >> Delta Vbe is good pretty easily to +/-1oC, uncalibrated. > >> > >> > There is an LM35 available in TO220. > >> > > >> > Zetex makes a cool 1K ohm SOT23 nickel RTD too. Nickel is cool because > >> > the curve slopes up, so you can linearize it by just loading it. RTDs > >> > are tough and don't rectify RF or oscillate. > >> > >> Can't argue with RTDs... > >> > >This has interesting measurements of a variety of vendors' 2n3904's: > > > >http://ww1.microchip.com/downloads/en/AppNotes/00001838A.pdf > > > > "Figure 2 also shows why true 2-terminal discrete diodes > > are not used in temperature sensing applications instead > > of 3-terminal devices such as the 2N3904. > > > > A discrete 2-terminal diode, ideally, would perform in > > temperature sensing applications as well as a thermal > > diode would. However, characterization in the labs > > determined that discrete 2-terminal diodes typically > > have an ideality factor much higher (1.2&ndash;1.5) than > > ? ASSUMED of 1.004. This discrepancy (between ? ASSUMED > > and ? REAL) would cause unacceptable temperature > > measurement errors at all temperatures." > > "Unacceptable" is arbitrary and judgemental. It's kinda prissy, going > around assuming stuff. > > > > >I just read a number delta Vbe app notes; all recommend diode-connected > >transistors over diodes. > > > >Cheers, > >James Arthur > > I don't care about ideality factor, how well a c-b junction might > match some theoretical ideal-diode equation. What matters is how well > you calibrate the V-T curve of a device, and how similar later devices > might be.
I sorta agree, If I could find a diode that was repeatable and easily calibrated against some standard that would be fine. The one nice thing about the 'ideal' behavior is that you can check the calibration (very roughly) by looking at the signal as a function of bias current. That nice.. and also nice physics. George h.
> > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics
On Tuesday, June 27, 2017 at 12:05:50 PM UTC-4, George Herold wrote:
> On Monday, June 26, 2017 at 9:02:31 PM UTC-4, dagmarg...@yahoo.com wrote: > > On Monday, June 26, 2017 at 8:17:45 PM UTC-4, dagmarg...@yahoo.com wrote: > > > On Monday, June 26, 2017 at 5:33:47 PM UTC-4, John Larkin wrote: > > > > On Mon, 26 Jun 2017 14:21:43 -0700 (PDT), dagmargoodboat@yahoo.com > > > > wrote: > > > > > > > > >On Monday, June 26, 2017 at 1:15:44 PM UTC-4, John Larkin wrote: > > > > >> On Mon, 26 Jun 2017 10:04:35 -0700 (PDT), dagmargoodboat@yahoo.com > > > > >> wrote: > > > > >> > > > > >> >On Monday, June 26, 2017 at 12:59:50 PM UTC-4, dagmarg...@yahoo.com wrote: > > > > >> >> On Monday, June 26, 2017 at 11:51:45 AM UTC-4, George Herold wrote: > > > > >> >> > I'm using a TIP31C (pnp in to-220 pac) as a temp sensor (diode connected) > > > > >> >> > There's a couple of depletion fets in series as current limiters. (LND150) > > > > >> >> > The b-e junction starts to zener at ~30 V (only two tested so far). > > > > >> >> > So I've got ~1.5 mA flowing at 30 V. Is this going to damage the junction? > > > > >> >> > Will it take time? I'm going to measure forward voltage again after > > > > >> >> > zenering for 15 minutes. Should I measure something else too? > > > > >> >> > > > > > >> >> > TIA > > > > >> >> > > > > > >> >> > George H. > > > > >> >> > > > > >> >> Why not just protect your TIP31C from zenering? A few diodes would do it. > > > > >> >> > > > > >> > > > > > >> >e.g., > > > > >> > | > > > > >> > +----. > > > > >> > | | > > > > >> >TIP31C |<' --- > > > > >> > .---| ^ D1 > > > > >> > | |\ | > > > > >> > | | | > > > > >> > '-----+----' > > > > >> > | > > > > >> > | > > > > >> > > > > > >> >Add a zener in series with D1 if you need to stand off some reverse voltage. > > > > >> > > > > > >> >Cheers, > > > > >> >James Arthur > > > > >> > > > > >> Or use the c-b junction instead. > > > > > > > > > >That loses the transistor action, degrading its temperature-sensing > > > > >performance. > > > > > > > > > >Cheers, > > > > >James Arthur > > > > > > > > Think so? It's still a diode with a roughly -2 mV/K tempco. > > > > > > I read that ages ago, in an early article about using Motorola transistors > > > specifically spec'd as temperature sensors IIRC. (It's amazing I can > > > remember that. Still have the article somewhere, I'm sure.) > > > > > > > No transistor will ever be a super-accurate temp sensor. > > > > > > Delta Vbe is good pretty easily to +/-1oC, uncalibrated. > > > > > > > There is an LM35 available in TO220. > > > > > > > > Zetex makes a cool 1K ohm SOT23 nickel RTD too. Nickel is cool because > > > > the curve slopes up, so you can linearize it by just loading it. RTDs > > > > are tough and don't rectify RF or oscillate. > > > > > > Can't argue with RTDs... > > > > > This has interesting measurements of a variety of vendors' 2n3904's: > > > > http://ww1.microchip.com/downloads/en/AppNotes/00001838A.pdf > > > > "Figure 2 also shows why true 2-terminal discrete diodes > > are not used in temperature sensing applications instead > > of 3-terminal devices such as the 2N3904. > > > > A discrete 2-terminal diode, ideally, would perform in > > temperature sensing applications as well as a thermal > > diode would. However, characterization in the labs > > determined that discrete 2-terminal diodes typically > > have an ideality factor much higher (1.2&ndash;1.5) than > > &eta; ASSUMED of 1.004. This discrepancy (between &eta; ASSUMED > > and &eta; REAL) would cause unacceptable temperature > > measurement errors at all temperatures." > > > > I just read a number delta Vbe app notes; all recommend diode-connected > > transistors over diodes. > > > > Cheers, > > James Arthur > > That's a nice paper. Do they say how they get the ideality factor? > I've got data (at different currents) for the tip32 and the error is > ~3 K if I assume fidelity factor = 1. Changing it to 1.003 (or so)
.................. ^ideality.. dang spell checkers. GH
> would make the numbers better. > > BTW here's a plot/table for tip32 at 10 uA of current. > https://www.dropbox.com/s/qxxoamj2hcn2nly/Diode%20calibration%20table.doc?dl=0 > > George H.
On Tuesday, June 27, 2017 at 12:08:49 PM UTC-4, George Herold wrote:
> On Monday, June 26, 2017 at 5:21:53 PM UTC-4, dagmarg...@yahoo.com wrote: > > On Monday, June 26, 2017 at 1:15:44 PM UTC-4, John Larkin wrote: > > > On Mon, 26 Jun 2017 10:04:35 -0700 (PDT), dagmargoodboat@yahoo.com > > > wrote: > > > > > > >On Monday, June 26, 2017 at 12:59:50 PM UTC-4, dagmarg...@yahoo.com wrote: > > > >> On Monday, June 26, 2017 at 11:51:45 AM UTC-4, George Herold wrote: > > > >> > I'm using a TIP31C (pnp in to-220 pac) as a temp sensor (diode connected) > > > >> > There's a couple of depletion fets in series as current limiters. (LND150) > > > >> > The b-e junction starts to zener at ~30 V (only two tested so far). > > > >> > So I've got ~1.5 mA flowing at 30 V. Is this going to damage the junction? > > > >> > Will it take time? I'm going to measure forward voltage again after > > > >> > zenering for 15 minutes. Should I measure something else too? > > > >> > > > > >> > TIA > > > >> > > > > >> > George H. > > > >> > > > >> Why not just protect your TIP31C from zenering? A few diodes would do it. > > > >> > > > > > > > >e.g., > > > > | > > > > +----. > > > > | | > > > >TIP31C |<' --- > > > > .---| ^ D1 > > > > | |\ | > > > > | | | > > > > '-----+----' > > > > | > > > > | > > > > > > > >Add a zener in series with D1 if you need to stand off some reverse voltage. > > > > > > > >Cheers, > > > >James Arthur > > > > > > Or use the c-b junction instead. > > > > That loses the transistor action, degrading its temperature-sensing > > performance. > > > > Cheers, > > James Arthur > > So I let the transistor zener through the night. In the morning the > forward voltage had changed by about 2 mV ~ 1 K.
Dang.. scratch that. I had a probe wire hanging on the base and when I took it off the voltage rose by ~1.5mV... RF? Anyway I need a cleaner environment for the measurements. GH
> > I'm going to recommend an LED in parallel, then when there is a reverse > voltage the LED will light! > > George H.
On Tue, 27 Jun 2017 09:12:14 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

>On Tuesday, June 27, 2017 at 10:02:22 AM UTC-4, John Larkin wrote: >> On Mon, 26 Jun 2017 18:02:21 -0700 (PDT), dagmargoodboat@yahoo.com >> wrote: >> >> >On Monday, June 26, 2017 at 8:17:45 PM UTC-4, dagmarg...@yahoo.com wrote: >> >> On Monday, June 26, 2017 at 5:33:47 PM UTC-4, John Larkin wrote: >> >> > On Mon, 26 Jun 2017 14:21:43 -0700 (PDT), dagmargoodboat@yahoo.com >> >> > wrote: >> >> > >> >> > >On Monday, June 26, 2017 at 1:15:44 PM UTC-4, John Larkin wrote: >> >> > >> On Mon, 26 Jun 2017 10:04:35 -0700 (PDT), dagmargoodboat@yahoo.com >> >> > >> wrote: >> >> > >> >> >> > >> >On Monday, June 26, 2017 at 12:59:50 PM UTC-4, dagmarg...@yahoo.com wrote: >> >> > >> >> On Monday, June 26, 2017 at 11:51:45 AM UTC-4, George Herold wrote: >> >> > >> >> > I'm using a TIP31C (pnp in to-220 pac) as a temp sensor (diode connected) >> >> > >> >> > There's a couple of depletion fets in series as current limiters. (LND150) >> >> > >> >> > The b-e junction starts to zener at ~30 V (only two tested so far). >> >> > >> >> > So I've got ~1.5 mA flowing at 30 V. Is this going to damage the junction? >> >> > >> >> > Will it take time? I'm going to measure forward voltage again after >> >> > >> >> > zenering for 15 minutes. Should I measure something else too? >> >> > >> >> > >> >> > >> >> > TIA >> >> > >> >> > >> >> > >> >> > George H. >> >> > >> >> >> >> > >> >> Why not just protect your TIP31C from zenering? A few diodes would do it. >> >> > >> >> >> >> > >> > >> >> > >> >e.g., >> >> > >> > | >> >> > >> > +----. >> >> > >> > | | >> >> > >> >TIP31C |<' --- >> >> > >> > .---| ^ D1 >> >> > >> > | |\ | >> >> > >> > | | | >> >> > >> > '-----+----' >> >> > >> > | >> >> > >> > | >> >> > >> > >> >> > >> >Add a zener in series with D1 if you need to stand off some reverse voltage. >> >> > >> > >> >> > >> >Cheers, >> >> > >> >James Arthur >> >> > >> >> >> > >> Or use the c-b junction instead. >> >> > > >> >> > >That loses the transistor action, degrading its temperature-sensing >> >> > >performance. >> >> > > >> >> > >Cheers, >> >> > >James Arthur >> >> > >> >> > Think so? It's still a diode with a roughly -2 mV/K tempco. >> >> >> >> I read that ages ago, in an early article about using Motorola transistors >> >> specifically spec'd as temperature sensors IIRC. (It's amazing I can >> >> remember that. Still have the article somewhere, I'm sure.) >> >> >> >> > No transistor will ever be a super-accurate temp sensor. >> >> >> >> Delta Vbe is good pretty easily to +/-1oC, uncalibrated. >> >> >> >> > There is an LM35 available in TO220. >> >> > >> >> > Zetex makes a cool 1K ohm SOT23 nickel RTD too. Nickel is cool because >> >> > the curve slopes up, so you can linearize it by just loading it. RTDs >> >> > are tough and don't rectify RF or oscillate. >> >> >> >> Can't argue with RTDs... >> >> >> >This has interesting measurements of a variety of vendors' 2n3904's: >> > >> >http://ww1.microchip.com/downloads/en/AppNotes/00001838A.pdf >> > >> > "Figure 2 also shows why true 2-terminal discrete diodes >> > are not used in temperature sensing applications instead >> > of 3-terminal devices such as the 2N3904. >> > >> > A discrete 2-terminal diode, ideally, would perform in >> > temperature sensing applications as well as a thermal >> > diode would. However, characterization in the labs >> > determined that discrete 2-terminal diodes typically >> > have an ideality factor much higher (1.2&#2013266070;1.5) than >> > ? ASSUMED of 1.004. This discrepancy (between ? ASSUMED >> > and ? REAL) would cause unacceptable temperature >> > measurement errors at all temperatures." >> >> "Unacceptable" is arbitrary and judgemental. It's kinda prissy, going >> around assuming stuff. >> >> > >> >I just read a number delta Vbe app notes; all recommend diode-connected >> >transistors over diodes. >> > >> >Cheers, >> >James Arthur >> >> I don't care about ideality factor, how well a c-b junction might >> match some theoretical ideal-diode equation. What matters is how well >> you calibrate the V-T curve of a device, and how similar later devices >> might be. > >I sorta agree, If I could find a diode that was repeatable and easily >calibrated against some standard that would be fine.
Buy the transistors from the same vendor, no matter how you process the signals. Ideally, but a reel that's a lifetime supply. Seems to me that you can't avoid some actual temperature measurements, unless you buy an IC or an RTD that has guaranteed specs.
> >The one nice thing about the 'ideal' behavior is that you can check the >calibration (very roughly) by looking at the signal as a function of bias >current. That nice.. and also nice physics. > >George h.
In your production units, are you planning to do the theoretical delta-I/deltaV math, or are you just going to use a constant current and measure the diode voltage drop? How accurate do you need it to be? -- John Larkin Highland Technology, Inc lunatic fringe electronics
On Tuesday, June 27, 2017 at 10:02:22 AM UTC-4, John Larkin wrote:
> On Mon, 26 Jun 2017 18:02:21 -0700 (PDT), dagmargoodboat@yahoo.com > wrote: > > >On Monday, June 26, 2017 at 8:17:45 PM UTC-4, dagmarg...@yahoo.com wrote: > >> On Monday, June 26, 2017 at 5:33:47 PM UTC-4, John Larkin wrote: > >> > On Mon, 26 Jun 2017 14:21:43 -0700 (PDT), dagmargoodboat@yahoo.com > >> > wrote: > >> > > >> > >On Monday, June 26, 2017 at 1:15:44 PM UTC-4, John Larkin wrote: > >> > >> On Mon, 26 Jun 2017 10:04:35 -0700 (PDT), dagmargoodboat@yahoo.com > >> > >> wrote: > >> > >> > >> > >> >On Monday, June 26, 2017 at 12:59:50 PM UTC-4, dagmarg...@yahoo.com wrote: > >> > >> >> On Monday, June 26, 2017 at 11:51:45 AM UTC-4, George Herold wrote: > >> > >> >> > I'm using a TIP31C (pnp in to-220 pac) as a temp sensor (diode connected) > >> > >> >> > There's a couple of depletion fets in series as current limiters. (LND150) > >> > >> >> > The b-e junction starts to zener at ~30 V (only two tested so far). > >> > >> >> > So I've got ~1.5 mA flowing at 30 V. Is this going to damage the junction? > >> > >> >> > Will it take time? I'm going to measure forward voltage again after > >> > >> >> > zenering for 15 minutes. Should I measure something else too? > >> > >> >> > > >> > >> >> > TIA > >> > >> >> > > >> > >> >> > George H. > >> > >> >> > >> > >> >> Why not just protect your TIP31C from zenering? A few diodes would do it. > >> > >> >> > >> > >> > > >> > >> >e.g., > >> > >> > | > >> > >> > +----. > >> > >> > | | > >> > >> >TIP31C |<' --- > >> > >> > .---| ^ D1 > >> > >> > | |\ | > >> > >> > | | | > >> > >> > '-----+----' > >> > >> > | > >> > >> > | > >> > >> > > >> > >> >Add a zener in series with D1 if you need to stand off some reverse voltage. > >> > >> > > >> > >> >Cheers, > >> > >> >James Arthur > >> > >> > >> > >> Or use the c-b junction instead. > >> > > > >> > >That loses the transistor action, degrading its temperature-sensing > >> > >performance. > >> > > > >> > >Cheers, > >> > >James Arthur > >> > > >> > Think so? It's still a diode with a roughly -2 mV/K tempco. > >> > >> I read that ages ago, in an early article about using Motorola transistors > >> specifically spec'd as temperature sensors IIRC. (It's amazing I can > >> remember that. Still have the article somewhere, I'm sure.) > >> > >> > No transistor will ever be a super-accurate temp sensor. > >> > >> Delta Vbe is good pretty easily to +/-1oC, uncalibrated. > >> > >> > There is an LM35 available in TO220. > >> > > >> > Zetex makes a cool 1K ohm SOT23 nickel RTD too. Nickel is cool because > >> > the curve slopes up, so you can linearize it by just loading it. RTDs > >> > are tough and don't rectify RF or oscillate. > >> > >> Can't argue with RTDs... > >> > >This has interesting measurements of a variety of vendors' 2n3904's: > > > >http://ww1.microchip.com/downloads/en/AppNotes/00001838A.pdf > > > > "Figure 2 also shows why true 2-terminal discrete diodes > > are not used in temperature sensing applications instead > > of 3-terminal devices such as the 2N3904. > > > > A discrete 2-terminal diode, ideally, would perform in > > temperature sensing applications as well as a thermal > > diode would. However, characterization in the labs > > determined that discrete 2-terminal diodes typically > > have an ideality factor much higher (1.2&ndash;1.5) than > > ? ASSUMED of 1.004. This discrepancy (between ? ASSUMED > > and ? REAL) would cause unacceptable temperature > > measurement errors at all temperatures." > > "Unacceptable" is arbitrary and judgemental. It's kinda prissy, going > around assuming stuff.
If we stop being offended and look at the figures, though, discrete diodes had large and unpredictable variations, while transistors' variations were small and consistent. That's what I got from the same paragraph, anyhow.
> >I just read a number delta Vbe app notes; all recommend diode-connected > >transistors over diodes. > > > > I don't care about ideality factor, how well a c-b junction might > match some theoretical ideal-diode equation. What matters is how well > you calibrate the V-T curve of a device, and how similar later devices > might be.
I've no quarrel with that. If you're going to individually calibrate the sensor anyhow, any diode will do and ideality doesn't matter. It seems the advantage of a diode-connected transistor is being repeatable and interchangeable /without/ calibration. Which is what George wants, AIUI. Cheers, James Arthur
On Tuesday, June 27, 2017 at 12:51:20 PM UTC-4, John Larkin wrote:
> On Tue, 27 Jun 2017 09:12:14 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote: > > >On Tuesday, June 27, 2017 at 10:02:22 AM UTC-4, John Larkin wrote: > >> On Mon, 26 Jun 2017 18:02:21 -0700 (PDT), dagmargoodboat@yahoo.com > >> wrote: > >> > >> >On Monday, June 26, 2017 at 8:17:45 PM UTC-4, dagmarg...@yahoo.com wrote: > >> >> On Monday, June 26, 2017 at 5:33:47 PM UTC-4, John Larkin wrote: > >> >> > On Mon, 26 Jun 2017 14:21:43 -0700 (PDT), dagmargoodboat@yahoo.com > >> >> > wrote: > >> >> > > >> >> > >On Monday, June 26, 2017 at 1:15:44 PM UTC-4, John Larkin wrote: > >> >> > >> On Mon, 26 Jun 2017 10:04:35 -0700 (PDT), dagmargoodboat@yahoo.com > >> >> > >> wrote: > >> >> > >> > >> >> > >> >On Monday, June 26, 2017 at 12:59:50 PM UTC-4, dagmarg...@yahoo.com wrote: > >> >> > >> >> On Monday, June 26, 2017 at 11:51:45 AM UTC-4, George Herold wrote: > >> >> > >> >> > I'm using a TIP31C (pnp in to-220 pac) as a temp sensor (diode connected) > >> >> > >> >> > There's a couple of depletion fets in series as current limiters. (LND150) > >> >> > >> >> > The b-e junction starts to zener at ~30 V (only two tested so far). > >> >> > >> >> > So I've got ~1.5 mA flowing at 30 V. Is this going to damage the junction? > >> >> > >> >> > Will it take time? I'm going to measure forward voltage again after > >> >> > >> >> > zenering for 15 minutes. Should I measure something else too? > >> >> > >> >> > > >> >> > >> >> > TIA > >> >> > >> >> > > >> >> > >> >> > George H. > >> >> > >> >> > >> >> > >> >> Why not just protect your TIP31C from zenering? A few diodes would do it. > >> >> > >> >> > >> >> > >> > > >> >> > >> >e.g., > >> >> > >> > | > >> >> > >> > +----. > >> >> > >> > | | > >> >> > >> >TIP31C |<' --- > >> >> > >> > .---| ^ D1 > >> >> > >> > | |\ | > >> >> > >> > | | | > >> >> > >> > '-----+----' > >> >> > >> > | > >> >> > >> > | > >> >> > >> > > >> >> > >> >Add a zener in series with D1 if you need to stand off some reverse voltage. > >> >> > >> > > >> >> > >> >Cheers, > >> >> > >> >James Arthur > >> >> > >> > >> >> > >> Or use the c-b junction instead. > >> >> > > > >> >> > >That loses the transistor action, degrading its temperature-sensing > >> >> > >performance. > >> >> > > > >> >> > >Cheers, > >> >> > >James Arthur > >> >> > > >> >> > Think so? It's still a diode with a roughly -2 mV/K tempco. > >> >> > >> >> I read that ages ago, in an early article about using Motorola transistors > >> >> specifically spec'd as temperature sensors IIRC. (It's amazing I can > >> >> remember that. Still have the article somewhere, I'm sure.) > >> >> > >> >> > No transistor will ever be a super-accurate temp sensor. > >> >> > >> >> Delta Vbe is good pretty easily to +/-1oC, uncalibrated. > >> >> > >> >> > There is an LM35 available in TO220. > >> >> > > >> >> > Zetex makes a cool 1K ohm SOT23 nickel RTD too. Nickel is cool because > >> >> > the curve slopes up, so you can linearize it by just loading it. RTDs > >> >> > are tough and don't rectify RF or oscillate. > >> >> > >> >> Can't argue with RTDs... > >> >> > >> >This has interesting measurements of a variety of vendors' 2n3904's: > >> > > >> >http://ww1.microchip.com/downloads/en/AppNotes/00001838A.pdf > >> > > >> > "Figure 2 also shows why true 2-terminal discrete diodes > >> > are not used in temperature sensing applications instead > >> > of 3-terminal devices such as the 2N3904. > >> > > >> > A discrete 2-terminal diode, ideally, would perform in > >> > temperature sensing applications as well as a thermal > >> > diode would. However, characterization in the labs > >> > determined that discrete 2-terminal diodes typically > >> > have an ideality factor much higher (1.2&ndash;1.5) than > >> > ? ASSUMED of 1.004. This discrepancy (between ? ASSUMED > >> > and ? REAL) would cause unacceptable temperature > >> > measurement errors at all temperatures." > >> > >> "Unacceptable" is arbitrary and judgemental. It's kinda prissy, going > >> around assuming stuff. > >> > >> > > >> >I just read a number delta Vbe app notes; all recommend diode-connected > >> >transistors over diodes. > >> > > >> >Cheers, > >> >James Arthur > >> > >> I don't care about ideality factor, how well a c-b junction might > >> match some theoretical ideal-diode equation. What matters is how well > >> you calibrate the V-T curve of a device, and how similar later devices > >> might be. > > > >I sorta agree, If I could find a diode that was repeatable and easily > >calibrated against some standard that would be fine. > > Buy the transistors from the same vendor, no matter how you process > the signals. Ideally, but a reel that's a lifetime supply. > > Seems to me that you can't avoid some actual temperature measurements, > unless you buy an IC or an RTD that has guaranteed specs.
That, or use the delta Vbe technique (take the Vbe at two currents, then subtract to get the difference).
> >The one nice thing about the 'ideal' behavior is that you can check the > >calibration (very roughly) by looking at the signal as a function of bias > >current. That nice.. and also nice physics. > > > >George h. > > In your production units, are you planning to do the theoretical > delta-I/deltaV math, or are you just going to use a constant current > and measure the diode voltage drop? > > How accurate do you need it to be?
That's really the question. That, cost budget, and whether George can calibrate the sensor or not. Cheers, James Arthur
On Tuesday, June 27, 2017 at 12:08:49 PM UTC-4, George Herold wrote:
> On Monday, June 26, 2017 at 5:21:53 PM UTC-4, dagmarg...@yahoo.com wrote: > > On Monday, June 26, 2017 at 1:15:44 PM UTC-4, John Larkin wrote: > > > On Mon, 26 Jun 2017 10:04:35 -0700 (PDT), dagmargoodboat@yahoo.com > > > wrote: > > > > > > >On Monday, June 26, 2017 at 12:59:50 PM UTC-4, dagmarg...@yahoo.com wrote: > > > >> On Monday, June 26, 2017 at 11:51:45 AM UTC-4, George Herold wrote: > > > >> > I'm using a TIP31C (pnp in to-220 pac) as a temp sensor (diode connected) > > > >> > There's a couple of depletion fets in series as current limiters. (LND150) > > > >> > The b-e junction starts to zener at ~30 V (only two tested so far). > > > >> > So I've got ~1.5 mA flowing at 30 V. Is this going to damage the junction? > > > >> > Will it take time? I'm going to measure forward voltage again after > > > >> > zenering for 15 minutes. Should I measure something else too? > > > >> > > > > >> > TIA > > > >> > > > > >> > George H. > > > >> > > > >> Why not just protect your TIP31C from zenering? A few diodes would do it. > > > >> > > > > > > > >e.g., > > > > | > > > > +----. > > > > | | > > > >TIP31C |<' --- > > > > .---| ^ D1 > > > > | |\ | > > > > | | | > > > > '-----+----' > > > > | > > > > | > > > > > > > >Add a zener in series with D1 if you need to stand off some reverse voltage. > > > > > > > >Cheers, > > > >James Arthur > > > > > > Or use the c-b junction instead. > > > > That loses the transistor action, degrading its temperature-sensing > > performance. > > > > Cheers, > > James Arthur > > So I let the transistor zener through the night. In the morning the > forward voltage had changed by about 2 mV ~ 1 K. > > I'm going to recommend an LED in parallel, then when there is a reverse > voltage the LED will light!
The LED is a fine solution, simple and rugged. Just don't shine any bright lights on it! Cheers, James Arthur
On Tue, 27 Jun 2017 10:11:48 -0700 (PDT), dagmargoodboat@yahoo.com
wrote:

[snip]
> >That, or use the delta Vbe technique (take the Vbe at two currents, then >subtract to get the difference). >
[snip] Page AN45-7 <http://www.analog-innovations.com/SED/Measurements_Including_TemperatureSensors_JimWilliams_AN45_.pdf> which I've successively implemented on several custom chips (with embellished mirrors and switching). ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I'm looking for work... see my website. Thinking outside the box... producing elegant solutions.
On Tuesday, June 27, 2017 at 7:06:34 AM UTC-7, John Larkin wrote:
> On Mon, 26 Jun 2017 20:56:56 -0700 (PDT), whit3rd <whit3rd@gmail.com> > wrote:
> LM35 IS a transistor used as a temp sensor (with linearizing > >tricks and a preamplifier).
> It's a modified bandgap reference. And it's specified for temperature > sensing accuracy.
That's backwards. Bandgap references use a balancing trick to null the tempco enirely, they're TERRIBLE temp sensors. But, they ARE transistor-forward-bias-based.
>> Software is just as good at linearizing, and a transistor makes a very good sensor.
> A transistor sensor will not be calibrated.
In the LM35 data sheet there's a plot of absolute accuracy limits, that necks down to a tight tolerance... at 25 C. That's what you get when you laser-trim resistors at one and only one temperature. LM35 is manufactured, calibrated, and then you solder it in. A transistor is manufactured, you solder it in, and then you calibrate it. The only difference is who does the calibration. Either way, the adherence to the theoretical curve allows a one-point calibration.