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I know that it can also be estimated by extrapolation, but I would like to determine the Early voltage from the Ebers-Moll equation. The equation I want to use is: enter image description here Where Is = saturation current. Ut = Thermal voltage, Uf = Forward voltage, Ic = Collector current, Uce = Collector-Emitter voltage

I tried to determine Is from the behavior of the B-E PN junction, which turned out to be an extremely small value for the BC547C Is ~ 4.2741E-14.

enter image description here enter image description here

If I calculate with this value, I get a surprisingly accurate value for Uf. However, if I calculate with this saturation current, a very large value is obtained for the early voltage.

My problem is determining the saturation current. How can I determine the saturation current?

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  • \$\begingroup\$ But IS will be small for BC547C will be around 4.679E-14A and V_A = 52.64V in the simulation of course. \$\endgroup\$
    – G36
    Commented Jul 8 at 19:49
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    \$\begingroup\$ Are you trying to come up with circuits that demonstrate the parameter values in a simulator? Or do you want to know how to plot things on a chart, taking measurements with real devices? Or what? Also, you do realize that the model used by simulators involves a great deal more than you are dealing with, right? \$\endgroup\$
    – periblepsis
    Commented Jul 8 at 20:56
  • \$\begingroup\$ Read this en.wikipedia.org/wiki/Early_effect BetaF= BetaFo * (1+ Vce/Va) \$\endgroup\$
    – Antonio51
    Commented Jul 8 at 21:23
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    \$\begingroup\$ @slimcolt It is trivial to get simulation to show where Is is at for a model. Even in the far more sophisticated case of Spice models that take into account the formation of emitter-base surface channels, the recombination of surface carriers, and the recombination of carriers in the emitter-base space-charge layer. The same is true for VA. And for the emission coefficient. Is that all this is about? Just getting a simulator output that you can read? \$\endgroup\$
    – periblepsis
    Commented Jul 9 at 12:48
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    \$\begingroup\$ @slimcolt The 2N2222 has a saturation current of Is=1E-14 and an emission coefficient of 1 (which means 60 mV per decade change of current) and an Early Effect voltage of VA=100. This circuit and plot uses a green arrow to demonstrate Is and a blue circle and lines to show that there is just 60 mV per decade change of the collector current. All in one chart. And this chart shows the Early Effect is at Va=100, just as the model says it should be. So what's going on? What are your questions here? I'm flummoxed. \$\endgroup\$
    – periblepsis
    Commented Jul 9 at 13:24

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Early effect is more shown than demonstrated.
Made wit Maple and Syrup box.
Effect Early voltage appears in the model of a BJT at the Fcb current-controlled source factor aF.

enter image description here

enter image description here

Example of an Early voltage of 5 V (horizontal axis "Vcc" from -5 V to 5 V).
The vertical axis is "Ic" current.

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