Diode

See forward conduction and reverse blocking in a junction diode with a current-limiting resistor.

A 5 V source feeds R1 = 1 kΩ and D1. The diode’s anode faces the resistor and its cathode faces ground. Vd measures anode-to-cathode voltage; Id measures forward current.

$$I_D=I_S\left(e^{V_D/(nV_T)}-1\right)$$ $$I_D=\frac{5-V_D}{1\,\mathrm{k\Omega}}$$

At 27 °C, with saturation current 10 fA and emission coefficient 1, the model gives Vd ≈ 0.693 V and Id ≈ 4.307 mA. The diode drop follows current and temperature; it is not a fixed 0.7 V.

Try it. Change V1’s DC voltage to −5 V. The diode becomes reverse-biased and current falls to a tiny reverse leakage. At this scale, the simulator’s numerical conductance can exceed the model’s 10 fA saturation current. Restore +5 V. Run the operating-point simulation after each change.

Read the table. Vd is green and Id blue. Positive current flows from anode to cathode. The series resistor limits forward current.

Model limits. D1 is a generic junction model, not a particular part. Series resistance, junction capacitance and transit time are set to zero here to isolate its static behavior. Reverse breakdown is outside the selected voltage range.