I'm trying to simulate a Common Emitter circuit using Proteus. The NPN transistor which I fetched from 'DEVICE' Library has a value of VBE = 0.77V What I want is to adjust this property to 0.6V. When I right click on the component and select 'Display Model Help' there are some initial parameters like in the figure below. My question is that, is there a way to adjust these parameters arbitrarily?

Model Parameters for NPN Transistor

  • \$\begingroup\$ For what collector current you want to get this 0.6V? \$\endgroup\$
    – G36
    Commented Apr 20, 2019 at 15:46
  • \$\begingroup\$ For just 1mA. Isn't it logical? Should I check Ebers-Moll equation? \$\endgroup\$ Commented Apr 20, 2019 at 15:48
  • \$\begingroup\$ Try to use this one \$I_S = I_C \cdot e^{\frac{-V_{BE}}{V_T}} = 1mA * e^{\frac{-0.6V}{ 25.86492mV}} = 8.43E-14\$ \$\endgroup\$
    – G36
    Commented Apr 20, 2019 at 15:59
  • \$\begingroup\$ I used this Spice model in Proteus \<*SCRIPT SPICE .model NP NPN(BF=100 IS=8.43E-14) *ENDSCRIPT>\ and <SPICEMODEL=NP > more you can find here youspice.com/how-to-import-pspice-models-into-proteus/3 \$\endgroup\$
    – G36
    Commented Apr 20, 2019 at 16:29

1 Answer 1


I found what to do :) The problem was that I thought that for every value of collector current the voltage between base and emitter remains constant. But, it was completely wrong. As stated in the Ebers-Moll model, there is a formula for this kind of situations.(The guy with G36 nickname mentioned that in the comments.)

$$ I_S = I_C \cdot e^{\frac{-V_{BE}}{V_T}} = 1mA * e^{\frac{-0.6V}{ 25.86492mV}} $$

Using this formula, we find $$ I_S = 8.43E-14 $$

And then the final thing is to adjust this parameter in Proteus. To do that,

  1. Right click the NPN Transistor component,
  2. Select 'Edit Properties'
  3. Tick the box 'Edit all properties as text'
  4. Then append the following line into the text box. (Don't include arrows :D )>> IS=8.43e-14

Click OK, and you are ready to go.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.