TOP264EG - Efficiency Improvements

Hello,

We are currently working on a new project in which we are using the TOP264EG component of the TOPSwitch-JX series. The prototype circuit was created on the basis of PiExpert. In the appendix is the PiExpert file of the circuit (5.25V / 4A output)
The transformers used were wrapped and manufactured according to PiExpert's prescribed Transformer Construction Guidelines. The default BOM was used for all remaining components.

We are now working on the efficiency of the power supply. As sources and literature we use, among other things, The Application Note-47. We were able to filter out some optimization guidelines here, but there are still questions and we hope you can answer these:

- RCDZ Clamp (p.11 - Figure 13b) - Are the identical values of PiExperts RCD + Z Clamp used here or are there corresponding calculation formulas for this? / What is the function of resistance R3?

- Line Sense Resistor Values (page 27) - Here, the application increase the resistance values of R1 + R2, thereby reducing the no-load input power dissipation. To compensate the UV threshold, R12 is selected between the CONTROL and VOLTAGE MONITOR pins. - How do I calculate the value of R12?

Thanks in advance for your support.