The formula that I made a lucky guess on above now makes a lot more sense to me. It's hard to read the datasheet with enough detail to get this right, but at least in LTspice simulation, it's a pretty consistent ~18mV per doubling in current across the useful range of the 2N3906

So, you are unaware of Shockley equations?

ΔVbe = Vt *ln (Ic2/Ic1) ≈ 26mV*ln(10) ≈ 60mV if Ic2 is 10 time Ic1

or if Ic2 is two times Ic1 we have

ΔVbe ≈ Vt *ln (Ic2/Ic1) ≈ 26mV*ln(2) ≈ 18mV

Also, keep in mind that Vt voltage (Thermal Voltage) is temperature-dependent.

 

keep in mind that Vt voltage (Thermal Voltage) is temperature-dependent.

Yes, the current-limit will have a temperature dependence, which likely is not a problem for most current-limit applications.
It could be if used as a constant-current source for a critical circuit.

 

So, you are unaware of Shockley equations?

ΔVbe = Vt *ln (Ic2/Ic1) ≈ 26mV*ln(10) ≈ 60mV if Ic2 is 10 time Ic1

or if Ic2 is two times Ic1 we have

ΔVbe ≈ Vt *ln (Ic2/Ic1) ≈ 26mV*ln(2) ≈ 18mV

Also, keep in mind that Vt voltage (Thermal Voltage) is temperature-dependent.

Yes, I was unaware. I've heard the name plenty of times, but hadn't learned the equations or their applications. Good stuff, thanks for sharing!