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I even don't know how this form can be induced. I know that I have to study more but I really want to know about this form please help (please ignore the actual value. I just want to know about formula)

Buker
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  • https://electronics.stackexchange.com/questions/502204/emitter-follower-class-a-amplifier/502218#502218 – G36 Oct 12 '20 at 15:29

1 Answers1

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You can derive this from the Shockley equation:

*Vbe = Vt(ln(Ic/Is)) so at two different currents Ic and Ic0 we have

\$V_{BE} - V_{BE0} \$ = \$V_T (\ln(I_C/I_S) - \ln(I_{C0}/I_S))\$ = \$V_T \cdot \ln (I_C/I_{C0})\$

At room temperature Vt = kT/q is about 25mV.

By using two currents, the saturation current Is cancels out, so you can predict the behavior independent of the device parameters.

* We can ignore the factor of 1 in the Shockley equation at reasonable currents >> Is.

Spehro Pefhany
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