Sure, let's try to add a buck converter to this schema.

The buck converter requires 4 components: an input capacitor (Cin), an output capacitor (C_OUT), an inductor (L), and a control switch, which is usually a transistor such as a MOSFET. Here are my suggestions:

Regarding the connections:

Also, remember the control and feedback circuitry to manage the switching of Q1. This will depend on whichever controller IC you decide to use, but the basic idea is to have the controller analyze output voltages and adjust the timing of the Q1 switching to maintain the desired output voltage.

Does this help you in setting up the Buck Converter schematic in Flux?

How to connect feedback pin

The feedback pin (VFB) is used to ensure our output voltage maintains its intended level. To connect it, we need to create a voltage divider network using two resistors. Let's call these resistors R1 and R2:

Then, make these connections:

This arrangement forms a circuit that measures a fraction of the output voltage and sends it back to the controller as feedback. The values of R1 and R2 will determine the output voltage according to this equation:

Where, $V_{FB}$ is the feedback voltage which is a constant specified by the manufacturer in the data sheet, and Vout is your desired output voltage.

Please adjust the values of R1 and R2 to get your desired output voltage. The exact values you need would depend on the specifications of your particular Buck converter.

Take note that the values chosen for R1 and R2 might change under different load conditions, so depending on your specific application, you might want to adjust these values accordingly.