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I have this circuit:
Assuming that the knee current is 0.2 mA and that the Zener voltage at current 5 mA is 7V. I would like to find the voltage across the load. I am however confused with the question since I assumed that the voltage across a Zener diode cannot go above it's Zener voltage, i.e. 7V, even if the answer of this question is 7.12 V. How come?
In the lower than rated current range, the Rs is inversely proportional to forward current until bulk series Rs dominates .
This really means the Rs is more logarithmic below rated current and more constant above rated current.
It is probably expecting you to use a more detailed zener model of the constant voltage model.
This is the model in Zener model in Sedra Smith. The slope is pretty linear so it basically models the Zener as a constant voltage in series with a resistance Rz.
You have the knee current, and the zener voltage and current deeper into the curve. But You seem to be missing the knee voltage required to calculate this slope. Do you have it?
