Secondary side feedback with TL-431 reference usually gives better than +/–5% output voltage regulation over line and load variations. The feedback components are displayed in the circuit diagram. The component values are calculated at the minimum input voltage.
Click the calculator icon 
to edit the component value. The 
icon will indicate that the custom value is specified.
To increase the phase margin of a design, select the Use Phase Boost Network check box. Then, the CF2 and RF4 values are calculated and added to the circuit diagram. PI Expert selects the Use Phase Boost Network check box automatically if the phase margin of a design is less than 45 degrees.
The Estimated Crossover Frequency and Estimated Phase Margin are calculated automatically reflecting the changes you make to the feedback component values.