Adjust diode temperature

[david_c_partridge]

I am using a 1N4148 as a temperature sensor in a thermostat circuit (reverse engineered).   I want to be able manually to set the temperature of JUST that one component in the circuit either while the simulation is running, or failing that between simulation runs.  The remaining components need to remain at "nominal temperature".

I'm hoping that the diode model will reduce Vf at about 2.3mV/degree as I change the temperature.   I tried Edit Model for the part, but there was no field to allow me to enter (e.g.) T_ABS)

[OStep · Accepted solution]

Correct, T_ABS is the model parameter you want to modify. If you're using a version of Multisim older than 11.0.0, then you will not see this parameter in the model parameter table of most diode components.

I've wrapped a 1n4148 in a subcircuit so that you have a raw text access to the model, in which you can specify T_ABS in the .model statement.

[david_c_partridge]

Thank you that does it - I just need to edit the model between runs to confirm - I guess there's no way to change it on the fly is there (so I can simulate warming and cooling)?

Also is it EG that will be the primary determinant of the temperature dependency of Vf?

[OStep]

No you can't change these parameters on the fly.

Operating temperature and its deviation from the measured temperature affect the forward region equation in several places. EG, which determines the saturation current Is, is only one such place.

See the attached document for the forward region equation and its parameters' dependence on temperature.

[david_c_partridge]

OK Thank you

[david_c_partridge]

The following model from Fairchild Semi seems to match the observed temperature dependence of Vf slightly better than the one you supplied, but nonetheless you put me firmly on the right track.

Is=5.84n N=1.94 Rs=.7017 Ikf=44.17m Xti=3 Eg=1.11 Cjo=.95p
+               M=.55 Vj=.75 Fc=.5 Isr=11.07n Nr=2.088 Bv=100 Ibv=100u Tt=11.07n T_ABS=110

Many thanks

Dave

[Keith_Taunton_UK]

Hi David. A little late as this is now April 2019. However, I thought I would give an 

answer in case others, like me, were looking for the same answer. Use the

PARAMETER SWEEP. YouTube will show you how.

https://www.youtube.com/watch?v=OfXXPmpdlEU

[tipa]

Health! Show in more detail how you do it. I also want to provide my models (MS-14) with the T_ABS parameter.
Thenks

[tipa]

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