[sdiy] [OT] PTAT with PN junction

[Czech Martin]

I have heard and measured that the forward drop of a diode
falls ~2 mV per degree Kelvin.

I have never seen a clear derivation of that.
Is the diode assumed to be fed by ideal current source?
Etc.

>From the ideal diode formula Is and q*T are responsible for
that, but we all know that thie ideal formula is not true
in reverse as well as in high current forward conduction.

I have seen transistor circuits with one BJT that should have
a larger rate at National.

I'm only 10 years within the semiconductor stuff, so no expert,
perhaps one of the old men can shed some light on that.

m.c.

-----Original Message-----
From: Tim Ressel [mailto:madhun2001 at yahoo.com]
Sent: Donnerstag, 13. März 2003 07:44
To: Synth-Diy
Subject: [sdiy] [OT] PTAT with PN junction


Hello to all semiconductor experts,

There seems to be a hole in my knowledge. I an using a
transistor PN junction as a temperature sensor (PTAT)
a la AN299. I am trying to determine die temperature
based on the Vbe so I can set the thermostat. How do
you determine the temperature based on Vbe?  I know
the Vbe at room temperature (25C) is 0.570V. The PN
junction is biased from a 10V sourse thru a 15K
resistor.

Thanks!

--TR


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