About PI Expert Bugs

Dear Kdedeoglu

Thank you very much for reaching out to us.


Design Results tab gives the user an overview on the worst case parameter values. These values may or may not synchronously happen at the same operating condition and/or tolerance combination.
On the other hand, Design Evaluation allows the user to discover how the power supply behaves at different input (input voltage), output (Load/set point) and tolerance combination (Current Limit and primary Inductance).
In practice, Design Result tab shows the maximum or minimum values of the electrical parameters across all tolerance conditions. The same values can be retrieved from design evaluation when the correct tolerance condition is selected.


It would be very helpful if you may please be more specific on what parameters and what conditions Design Result and Design Evaluation do not match. It also would be very helpful for us if you can share your design file with us so that we can have a more in depth look into it and verify if the behavior you described.


Thank you very much.


Best regards
PI- Star Lord

Dear PI-Star Lord

First of all, thank you for your quick response.

Our aim is to minimize the power dissipation as soon as possible. Since our smps is designed for very limited small case, power dissipation which causes temperature rise is very critical.

I am sharing design results and design evaluation parameters in attachment. As you see, most of the parameters are different in value.

Thank you.

Dear kdedeoglu
Thank you for sharing your design results.


Form what I can see in Design_Evaluation.pdf, the electrical parameter reported in the first table on the left side correspond to an operation where the Current Limit of the controller and the primary Inductance are both at the maximum tolerance corner ( ILIMIT Tolerance = MAX and LP Tolerance = MAX)
As explained above, the Design Result Tab (Device Variable Section) reports the worst case value of parameters like FS, KP, DMAX, etc...
The same parameters are also shown in Design Evaluation, but instead of looking at the worst case for each parameter, it shows one particular operation condition. In your specific example it is 100% load, 195 VAC, primary inductance and current limit both at the maximum tolerance value.


If you want to evaluate your power supply at nominal value of LP and ILIMIT, you just have to change the respective combo boxes in the Design Evaluation controls.


Now, if you want to match the values shown in the Design Report tab, I can show you how.
To match the value of FS, you need to set ILIMIT to MIN and LP to MIN, that's because the maximum switching frequency happens when the value of the inductance and current limit are at their minimum tolerance.
To match the value of KP and DMAX, you need to set ILIMIT to MIN and LP to MAX,
To match the value of IRMS and ISRMS, you need to set ILIMIT to MAX and LP to MIN.
This is to show that the worst case of different electrical parameters happens at different tolerance corners.


Now, coming to your problem, to minimize power dissipation, you would need to focus on one particular corner point (the most likely one: Nominal value of both current limit and primary inductance) than you could evaluate the power dissipation for other tolerance corners.


Hope this helps.

If you need more clarifications, do not hesitate to contact us.

Best regards
PI-Star Lord

Dear PI-Star Lord,

Thank you very much again for your quick response.

I can ask you another question in case of a problem. Thank you.