Base Emitter Voltage Equation

[jonnybgood]

Hi,
attached is a slide of an op amp voltage regulator design tutorial.

There is an equation for finding base emitter voltage involving a variable '10fA'.

What is this exactly and from which model is this equation derived?

 

[mister_rf]

That’s based on the Ebers-Moll equations.
In a bipolar transistor collector current Ic in a linear mode is related to the base-emitter voltage by the Ebers-Moll equation.
Bipolar junction transistor - Wikipedia, the free encyclopedia

26mV = is the thermal voltage = kT / q (approximately at 300 K ≈ room temperature).
10fA = is the reverse saturation current (on the order of 10⁻¹⁵ to 10⁻¹² Amperes)