Ideal diode equation is $$V(I)=\eta V_T \mathrm{log}(\frac{I}{I_s}+1)$$ Model:


simulate this circuit – Schematic created using CircuitLab

If the diode has an internal resistance \$r\$, a more realistic model, valid in the region where the diode conduces is $$V(I)=\eta V_T \mathrm{log}(\frac{I}{I_s}+1)+rI+V_0$$ Model:


simulate this circuit

Where \$V_0\$ is a constant voltage.

I think that \$V_0\$ is necessary for this model to work, but what does it actually represent?

What is exactly the role of \$V_0\$ in the model proposed?


1 Answer 1


A diode contains barrier potential Vo (typical 0.7 V for silicon and 0.3 V for Germanium)

In your model that is assumed to be the minimum potential that the diode can have when conducting. After that point it follows the curve assigned by that more complex log function.

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