Re: Converting a NTC voltage into temperature in Celcius

On 12/04/2025 12:22 am, Don wrote:

Bill Sloman wrote:

Don wrote:

brian wrote:
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<snip>
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I ended up using a diode as a temperature sensor as I
couldn't get it linear enough.

>
Interesting. Thank you for sharing. When operated in Zener mode (as
opposed to avalanche mode) a Zener diode's NTC apparently remains
approximately the same, regardless of orientation (forward or reverse
biased).

>
Whether a reverse biased diode breaks down in Zener mode or avalanche
mode depends entirely on the diode you have selected.
>
if it breaks down at less than 5V reverse voltage it is breaking down by
the Zener mechanism (with a negative temperature coefficient) , and if
it the breaks down at an 8V or a higher reverse voltage the avalanche
mechanism is dominant (with a positive temperature coefficient.
>
https://toshiba.semicon-storage.com/us/semiconductor/knowledge/faq/diode/are-there-any-special-considerations-for-the-temperature-coeffic.html
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doesn't exactly conform to your claim.

 My statement
      When operated in Zener mode (as opposed to avalanche mode)
 pertains Zener diodes in Zener mode. Why do you want to talk about the
positive temperature coefficient of Zeners in avalanche mode?

The problem is that you choose the mode when you choose the diode. Your formulation suggests that you think somebody could to operate one diode in one mode or the other. Only a hopeless newbie could think that, but some of the lurkers aren't all that sophisticated, and a few of our posters aren't much better.
Gerhard Hoffmann has pointed out that even a 4.7V zener diode has enough avalanche component in it's breakdown mechanism to introduce lots of noise though the temperature coefficient of the reverse voltage is still marginally negative.
--
Bill Sloman, Sydney