on the right of the parameter box. The 
icon indicates that a custom parameter value has been entered.Use the Key Parameters form to check and edit the power supply's advanced operating parameters.
The key parameters are calculated automatically when a new design is optimized for the first time. Editing the key parameters is recommended only if you are an advanced power supply designer.
Depending on the PI device family, different parameters are available for you to modify. To edit a parameter click the calculator icon on the right of the parameter box. The icon indicates that a custom parameter value has been entered.
The following key parameters are available:
Continuous/Discontinuous Operating Ratio (KP) is the ripple-to-peak current ratio of the primary current. For PWM device families (TOPSwitch-JX/HX/GX and DPA-Switch) this value is calculated and checked to be within acceptable limits. For all ON/OFF controlled device families (TinySwitch-4, TinySwitch-III, TinySwitch-II, and LinkSwitch-XT), this parameter is an output that is calculated at minimum current limit and cannot be modified. You can choose a value of KP for PWM based devices if you wish.
Efficiency Estimate (N), % is the ratio of total output power divided by total input power. Default values are defined at minimum AC operating voltage and are adjusted for the specified output voltage (see Application Note AN-29 for TOPSwitch-GX efficiency curves). The main output is used to determine the efficiency estimate. You can change the value if data from a tested prototype is available.
Reflected output voltage (VOR), V is the output winding voltage multiplied by the turns ratio and reflected back onto the primary winding during the primary Switch off-time. The best possible value for VOR is chosen during device optimization and is used primarily to affect the duty cycle of the power supply. You may enter a custom value of VOR to change the supply's operating characteristics.
Loss Allocation Factor (Z) is the allocation of power loss between the primary and secondary circuitry (secondary circuit losses divided by the total losses). PI Expert calculates a value between 0.4 and 0.8 that is scaled for device power capability. This factor increases when the minimum AC input voltage is increased and decreases when the DC output voltage is increased. You can change the value if data from a tested prototype is available.
Drain to Source Voltage (VDS), V is the estimated voltage drop across the primary Switch during conduction, averaged over the conduction period. You can change this value if a more accurate value is available from a prototype.
Feedback Pin Current (IFB), µA is the current going into the Feedback pin (FB). IFB must be between 85 µA and 210 µA under normal operating conditions, including variation in the LED string voltage. During dimming, as the feedback current reduces the maximum duty cycle will be limited in order to help improve the dimming range.
Maximum Flux Density (BM), Gauss is calculated automatically and you cannot change this value. You will get an error message while optimization if the recommended flux density value is exceeded, or if it is too low.
Main Turns (NSM) is the number of secondary turns on the main output. This value may be changed and will not affect VOR as primary turns will be recalculated. The optimization process will automatically try to choose the best compromise between the accuracy of outputs (if the supply has multiple outputs) and the lowest number of turns while checking that the windings will fit on the chosen bobbin.
Primary Number of Turns (NP) is the calculated number of primary turns given the VOR and main turns (NSM).
Primary Inductance (LP), µH is the calculated primary inductance value necessary to deliver the specified output power.
Nominal Primary Inductance (LP_nom), µH is the typical value of the calculated primary inductance. Within a certain tolerance of this value the power supply will still be able to deliver the specified output power, without having a flux density that is too high.
Tolerance (Lp_Tol), % is the primary inductance tolerance. You can modify this value.
Primary Leakage Inductance (L_LKG), µH is the estimated leakage inductance for the transformer based upon, device, power level and transformer construction. Overwrite this value if you have measured the leakage on prototype since the clamp is designed using this value of leakage.
Secondary Trace Inductance (LSEC), nH is the estimated secondary trace inductance. Although this value is low, it is reflected back on to the primary causing its effective inductance to be much larger. This contributes to the leakage inductance and, thus, affects the leakage spike that appears on the drain. The software takes this secondary inductance into account when designing the clamp. You can overwrite this value if you have measured the secondary trace inductance on a prototype.