In chapter 3 of the book Designing Control Loops for Linear and Switching Power Supplies: A Tutorial Guide, there is a figure 3.59:
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The expression of the divider ratio is as follows:
$$\alpha=\frac{R_{lower}}{R_{lower} + R_{upper}}$$
And the expression is derived from figure 3.58.
Why doesn't the divider ratio appear in the closed loop? I thought the divider ratio \$\frac{1}{\alpha}\$ should be placed inside the closed loop:
