[QUOTE = "Galacta, publicación: 1548763, miembro: 729783"]
¡Me las arreglé para que la simulación funcionara! Usé un modelo del TL431 que se encuentra en el apéndice 3B del libro. Esto, combinado con el circuito que se muestra a continuación, funcionó para revelar la respuesta correcta.
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Friend, I'm a beginner and I don't know where to start to implement this model in ltspice, could you help me?

Mod: translation.
I managed to get the simulation to work! I used a model of the TL431 found in appendix 3B of the book. This, combined with the circuitry shown below, worked to reveal the correct answer.

 

I managed to get the simulation working! I used a model of the TL431 found in appendix 3B of the book. This, combined with the circuit shown below worked to reveal the correct response.

Friend, I'm a beginner and I don't know where to start to implement this model in ltspice, could you help me?

 

Hello welcome,
The TI datasheet gives the following equivalent circuit. Not to be confused with An actual TL431 circuit.
One definition reads: an equivalent circuit refers to a theoretical circuit that retains all of the electrical characteristics of a given circuit. ... These more complex circuits often are called macromodels of the original circuit.

There are the three pins. You can dress up the circuit like figure 17 datasheet, you can change the op amp.