hi 5,
Have you considered that a 5mA current will create some self heating of the tran/diode.?
Also your plot starts at approx -1.2v for 0C, which would not be suitable for connection to a device [PIC ADC for example]
Re look at the R3 value, ideally 0.0Vout for 0Cdeg.

I will try a LTSim of your circuit, later.
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hi 5,
Look at these two LTS sim plots.
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hi 5,
Look at these two LTS sim plots.
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i tried to design it again with 5*10^-5 current and still iget that bad simulation, idk whats wrong tbh

 

hi 5,
I am not sure what you mean by bad, please explain.
Post your sim circuit diagram.
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hi 5,
I am not sure what you mean by bad, please explain.
Post your sim circuit diagram.
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Look at this orcad simulation :

 

hi,
Look at these plots for R2 and R3 currents.
The R2 and R3 currents have to be opposite and of the same magnitude.
Try R3 as a 39K , then adjust R4 for the correct overall gain.
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hi,
Look at these plots for R2 and R3 currents.
The R2 and R3 currents have to be opposite and of the same magnitude.
Try R3 as a 39K , then adjust R4 for the correct overall gain.
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when i try to analyze the circuit i see that current in R2 and R3 are the same, could u please take a look at the pictures that i attached earlier(i will attach it again here), and tell me if there are any mistakes? i really tried alot and im not sure what im doing wrong.
and i must get correct calculations so i can show it to the professor , correct result of simulation is not enough .

 

hi,
For BC109 you have Is=1.6384pA and you calc Vbe at 0Cdeg as 0.51394V

You show Vbe = (273/11600)* ln(5mA/1.6384pA) = 0.51397V
Where did you get the Is value and equation from.???

I make Vbe at 0Cdeg as ~0.64v.


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hi,
For BC109 you have Is=1.6384pA and you calc Vbe at 0Cdeg as 0.51394V

You show Vbe = 273/11600 ; ln(5mA/1.6384pA)
Where did you get the Is value from.???

I make Vbe at 0Cdeg as ~0.64v.


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i got the value from Orcad (from the transistor model settings)
because i couldnt find it in the datasheet on google.
could u please tell me how u made Vbe at 0Cdeg = 0.64?

 

hi,
Its derived from the results of the LTS sim.
As you may know Vbe falls by ~2mV for every 1Cdeg rise in temperature.

Look thru this PDF

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hi,
Its derived from the results of the LTS sim.
As you may know Vbe falls by ~2mV for every 1Cdeg rise in temperature.

Look thru this PDF

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Thanks a lot bro finally i solved it , the problem was the way i calculated VBE . i solved it by going to orcad and calculated VBE at 0 degree and at 100 degree then calculated Resistors depending on that and finally it gave me the correct answers.
really thanks

 

hi.
Pleased to hear that.
Post your final results so I can check the result.
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hi.
Pleased to hear that.
Post your final results so I can check the result.
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For BC109C npn transistor
R1 = 100k
R2 = 5k
R3 = 40.65k
R4 = 16.94k

 

hi 5,
Many thanks for the feedback, other students may benefit from your Thread.
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