Diode connected transistor as temp sensor

We had a lecturer whos introduction to a new class was to, apparently, gargle LN2.

Ya think? :)

--

John Devereux

[snip]

Most reference circuits utilize a "kick-start" loop to ensure power supply rejection by generating current sources related to its own reference potential.

These tend to be near leakage levels to minimize raw power feed-thru, thus probably struggle at very cold temperatures. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

      Remember: Once you go over the hill, you pick up speed

Spehro here. Yes, an integrated circuit. Specifically, an AD590.

Looking at the schematic (page 6):

.. looks like there's a loop of current mirrors that has to be fired up for it to function at all.

=A0 =A0 ...Jim Thompson

=A0 =A0| =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 |

quoted text -

Thanks Jim

George H.

ing

the

Thanks Sphero, Now that I think about I seem to remember something like that. (You've got to leave the power on for the AD590 to work.)

Still it'll be fun to try. Perhaps if I 'goose' it it'll come on.

George H.

the

voltage

in the

temperature.

outliers.

single point

accuracy

interested.

test.

integrated

AD590

your

special

77K.

not

will

I never said that; I said they wouldn't work at liquid nitrogen temps. The datasheet says they work to -55C, but doesn't explicate the latchup hazards.

John

2C) as a

h with the

orward voltage

and one in the

mperature.

the outliers.

forward

, single point

e K accuracy

interested.

quick test.

ng integrated

Device AD590

ating your

e special

or makes

wn to 77K.

rtainly not

tor

mV and

, it will

e post

at

e good

in

s -

a

when

ontent-

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ou

The question was why they wouldn't work at liquid nitogen temperatures. You gave one possible - imagined - failure mechanism, as opposed to an observation of what actually happens.

-- Bill Sloman, Nijmegen

Heard of that trick but never seen it done. Very very dangerous if you swallow some!

I do know of one popular science lecturer now retired who does hair washing with LN2 using a rubber pipe dipped into bulk liquid. This isn't quite as dangerous as it sounds provided you don't get it in your eye! (but is no longer considered acceptable in a risk averse culture)

Another infamously has his own LOX still powered by more easily available LN2 since the none of the suppliers will supply him any more.

There are still a few science popularisers around doing their bit to make chemistry seem interesting to the next generation with smoke, flashes, smells and bangs. School science is just too tame now.

Regards, Martin Brown

I did see it done, it was on my first day at uni :)

Most of us in the physics lab must have dipped our hand in the stuff at some point.

I think I'd prefer that to the hand in the solder stream trick, which then solidifies...

It was bad enough when I splurged hot melt glue on my hand :(

--

John Devereux

as a

with the

forward voltage

one in the

temperature.

outliers.

forward

single point

accuracy

interested.

quick test.

integrated

Device AD590

calibating your

special

makes

to 77K.

Certainly not

and

will

post

good

content-

point

Useless idiot. Test one and prove me wrong.

John

IP32C) as a

unch with the

e forward voltage

rs and one in the

temperature.

and the outliers.

er forward

ure, single point

gree K accuracy

be interested.

s a quick test.

using integrated

log Device AD590

libating your

the special

uctor makes

down to 77K.

Certainly not

ductor

600 mV and

M35, it will

the post

that

make good

ish in

ears -

ng a

ing

bad when

n content-

ess point

t

d you

n -

nd

0

Impractical suggestion - and irrelvant to the point I was making, which is that you were asked for information, and responded with an imagined fact (not for the first time, though most of your imagined facts comes out of the right-wing newspaeres you read).

-- Bil Sloman, Nijmegen

(TIP32C) as a

with the

forward voltage

and one in the

temperature.

the outliers.

forward

single point

K accuracy

interested.

quick test.

using integrated

Device AD590

calibating your

special

Semiconductor makes

down to 77K.

Certainly not

semi-conductor

mV and

it will

post

good

in

-

when

content-

point

I knew that!

and irrelvant to the point I was making,

I gave you information. Output is 10 mV/K, and there's a PN substrate diode that will conduct, usually latching up the chip, at -1 junction drop. If you still pretend that the LM35 will work at -2 volts out, well, hang on to that belief.

I don't have to build and test a bad circuit to know that it won't work. I supppose you do, which means that the only way you can design circuits is by testing random numbers and connections of components. Which, of course, isn't very effective because you don't test any circuits.

Useless idiot.

John

I heard the important thing under those conditions is to hold your breath no matter what!

Martin Brown Inscribed thus:

Your comment above reminded me of my school chemistry teacher, who one day was giving a lecture and demonstration of gun powder. He had mixed up a batch on a small anvil and was scraping a small quantity to one side and hitting it with a pin hammer borrowed from the woodwork master. I remember well the exceedingly loud bang, blinding flash, enormous cloud of black smoke, and the acrid smell, when he hit the wrong pile...

The head of the pin hammer disappeared through the ceiling tiles, never to be seen again ! In my minds eye I can still see the aghast look of shock and horror on his blackened face, even after nearly 55 years, and the hooting and cheering of us all.

--
Best Regards:
                          Baron.

s

You gave me information about your mental model of the LM35 - usefuk inits way, but not what was asked for.

I don't. What I wanted to know was whether this is what screws it up in real life.

The interesting question is not whether or not it would work, but where and why it would cease to work. You've got wound up about the LM35 which was one of the two integrated circuits I mentioned, and have managed to ignore the rather more interesting comments about the AD590, which looks as if it would work though probably only if it were powered up before it was cooled to 77K.

Another of your imagined pieces of infornation. Nobody designs circuits that way - it would take far too long. I do what everybody else does - sketch things on bits of paper, and think about them a bit. In recent years, sketching them into LTSpice and running a simulation or two has sometimes formed a part of thinking process.

-- Bill Sloman, Nijmegen

Impractical suggestion - and irrelvant to the point I was making, which is that you were asked for information, and responded with an imagined fact (not for the first time, though most of your imagined facts comes out of the right-wing newspaeres you read).

-- Bil Sloman, Nijmegen

His typing skills are getting worse and worse. Can't even get his name right anymore. At any rate, we need to treat this useless idiot the same way you would treat _any_ feces stirring troll. Ignore him. Does anyone here know what ignore him means? Hopefully the dipstick will just wither up and blow away.

[snip]

Start kill-filing the troll-feeders. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |

      Remember: Once you go over the hill, you pick up speed

ure

s.

e t

as

h

nd

.

on

s.

of

ve

s o

han

hat

old

de

100 e

s.

ght

u w

Kind of optimistic. I've been around for fifteen years, so the chance that I'll wither up and blow away in the immediate future is remote. But hifi-tek is a newby around here and probably doesn't know about that either.

I am mortal, and will eventually wither up and die, but my statistical expectation of life give me another fifteen to twenty year yet. The typing skills may fade before then, but reminding John Larkin that he can't think straight is one of those routine jobs that doesn't engage my full attention.

-- Bill Sloman, Nijmegen

Useless fathead. I'm designing electronics, and you aren't, so who is thinking straight?

And to position the word "job" anywhere near Sloman is a joke.

John