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As you can see, when V1 < V2, the "diode voltage source" can supply the input device:-)

Current "source"

We can even make (model) a diode by a "dynamic" current source changing its current in the same way when the voltage varies. Here are the arrangements for the three typical points on the curve.

Point 0: VF = 425 mV; IF = 0 mA.

^{simulate this circuit}

Point 1: VF = 644.3 mV, IF = 4 mA.

^{simulate this circuit}

Point 2: VF = 678.4 mV, IF = 8 mA.

^{simulate this circuit}

Implementation: "Active" diode

This idea is implemented in the so-called "active diode". As an example, let's make the schematic above this way.

^{simulate this circuit}

Here the transistor is a current "source" that adjusts its collector current so that to keep the respective voltage across itself.

See also my answer 1 and 2.

As we can see as the voltage increases the resistance decreases and the IV curve is almost vertical.

As we can see as the voltage increases the resistance decreases and the IV curve is almost vertical.

Thus, if you continuously adjust the resistance for each value of the input voltage, you will mimic the real diode. If you hide in a box together with the resistor, the outside observer will think that there is a diode inside :-)