A resistor-capacitor-diode clamp circuit can be used to limit the voltage at the switch node. The equations below can be used to determine initial values for the resistor and capacitor, but the circuit will need to be optimized through testing. First, calculate the clamp voltage by determining how much overshoot is allowable at the switch node.
The parameter KCLAMP defines the target overshoot value. For example, set KCLAMP to 1.5 for 50% allowable overshoot.
Next, the leakage inductance LL and peak primary current IPRI_MAX of the transformer can be used to approximate the clamp resistor. The clamp capacitor value can be determined thereafter. Note that ΔVCLAMP defines the allowable ripple for the clamp capacitor.