I want to observe the effect of the parallel RC circuit on the feedback line in the circuit shown in the image below, I even expect this added structure to provide a decrease in the rise time, but I could not create it in the LTspice simulation, how should I proceed? Since I don't know the structure of my feedback signal, I first tried it with a voltage source that increases over time and settles for a certain period of time, then I tried the relevant structure on the feedback pin of any IC, since the IC in the image does not have a spice model, but I still could not see the effect I expected, how can I observe it?

 

Without any voltage to the transistors there will be no output and thus no feedback. So if you add a resistor to some DC voltage positive relative to "GND2"in the circuit shown your simulator should work.
In addition, though, unless the function of that device U1 is defined adequately for your simulator, there is no connection in the feedback loop.
Feedback always requires an actual connection and the drawing presented does not include any connection. So there is no feedback loop, and as drawn, no feedback signal, either. So there are two reasons why it does not work.

 

Since this is not available on the integrated Ltspice, I tried to draw the feedback line (without transistor) and add this parallel RC circuit in series, but I could not get the desired result. I foresee an instantaneous voltage of around 400v coming from the coil to the feedback line, can't I simulate it this way?

 

Coil? Who mentioned a coil?

 

Coil? Who mentioned a coil?

The fact is that simulator software is no better at mind reading than I am, which is to say POOR. I see the connections heading off thru a connector, but both the coil and the connection to the other end of the coil are not available for the simulator to use.
In fact, none of the circuit as presented is in the format that the simulator uses. So the very best that any here can do is a guess at what was presented to the simulator.

 

Hello,

You already have a thread for this:
https://forum.allaboutcircuits.com/threads/parallel-rc-circuit-in-feedback-reading-line.191143/

Bertus