Use the Fast Surge Protection Circuit form to review the components used in a circuit that will quickly interrupt switching in order to protect the primary Switch.
PI Expert provides some initial values for the fast surge protection circuit.
This circuit consists of a resistor divider that will be checking the rectified AC voltage. If the voltage is higher than the zener voltage together with the two small signal diodes, then a signal will be injected into the V pin of the LinkSwitch-PH and the PI Deivce will stop switching.
Two small signal diodes are used in order to guarantee that when the zener is off, the leakage current through the parasitic capacitance will have a negligible effect on output regulation. Careful layout is necessary as these two diodes should be placed as close as possible to the V pin.
You can change the components by clicking the calculator icon 
on the right of each component in the damper components box. The dialog boxes where you can select another component will be displayed as the following:
The Zener dialog box – for the Zener diode
The Diode dialog box – for both small signal diodes
The Resistor dialog box - for the resistors
Select the component you want to add, or edit the resistor parameters when changing the resistor. Click OK.
The 
icon indicates that a custom parameter value has been entered. Click the icon to restore the default automatically selected value.