Re: Question about diode temperature and forward voltage

Thanks but do you know how to derive an equation so I can get dVf / dT
= -2mv / C ?

Jamie wrote:
acataldo@xxxxxxxxx wrote:

I'm trying to understand how a diode can be used to detect changes in
temperature. According to all the literature I've read, a diode's
forward voltage, Vf, falls by 2 mV for every 1 degree C increase in
temperature. This doesn't seem to agree with the diode equation, which
suggests that Vf should increase with temperature.

Vf = k*T/q * ln( If / Is)

What am I missing?

what your missing is the way it's being used
in the circuit.
diodes start conducting better as they get
warmer.
if you were to have a diode in a series
circuit and measure voltage that way, then you
would get the increase as indicated how ever
what i think your looking at is the diode being
used as a shunt load..
as the diode warms up it conducts better and there
for dropping the voltage on the load.
normally 2 diodes in series are used into a pot that
drive's the base of a transistor.
the pot, is to calibrate the bias point.



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