icon will indicate that the custom diode is chosen.Secondary side feedback with a Zener diode reference usually gives about +/–7% output voltage regulation over line, load, and temperature variations. The feedback components are displayed in the circuit diagram. The component values are calculated at the minimum input voltage.
Zener diode determines the output voltage set point. PI Expert selects the diode from the Zeners Library when creating the design. The following diode parameters are displayed:
Part Number
Rated Voltage, V (avalanche breakdown)
Tolerance, % (of its breakdown voltage)
Power Dissipation, mW (when operating at the output voltage set-point with the specified values of RF1 and RF2)
Zener Test Current, mA of the diode.
Click Change to select a different Zener diode from the Zeners Library. The icon will indicate that the custom diode is chosen.
Click Default to move back to Zener diode selected by PI Expert when creating the design.
RF1 is the bias resistor for the Zener diode. This resistor is selected to bias the zener close to its zener test current to give the best possible accuracy.
RF2 is the compensation resistor, sets the gain of the feedback loop.
Click the calculator icon 
to edit the component value. The icon will indicate that the custom value is specified.