LNK6779E Design Ambiguity with Rc2

2 posts / 0 new

I am designing a dual output fly-back converter with PI Expert. The design "compiles" with no errors
or warnings. I am outputting 15V and 24V from a 100V to 265 VAC input @ about 100 Watts total.

The RCDZ circuit specified has a Rc2 value of 4.7Kohm but it says there should be 5 of them. (And in the generated
BOM, there are 5 reference designators assigned to them. )

What the schematic does NOT say is how these 5 should be connected (in series? in parallel?). Either configuration
is outside the range specified for Rc2 in application not AN-58.

Which configuration is it?

Dear Julio.

Thank you for reaching out to us.
Generally when PIExpert indicates that there should be 2 or more of the same resistor, then, those resistors must be connected in parallel.
You can verify this yourself by following the steps below.

  • 1--> Right click on the Rc2 resitor in your schematic in PIExpert
  • 2--> Click on Functional Dialog
  • 3--> In the Section RCD Clamp, hover over the drop down list of the varialbe Number of RC resistors
  • 4-> The tooltip Number of paraller Clamp Resistors should appear.

Regarding the suggested value of the Resistor, in order to properly asses its correctness, I would need to take a look at the design and its main parameters, like Switching Frequency, Reflected output voltage, Leakage inductance, Primary peak current, etc..

You can share your design by:

  1. 1-->Save your design
  2. 2-->Click: File --> File Manager
  3. 3-->Click Share (last column in the design list)
  4. 4-->Click Get Link icon (Next to the Share Icon)
  5. 5-->Copy the URL onto your clipboard
  6. 6-->Post the hiperlink on this very forum for me to take a look.

Hope this may help
Thank you very much.

Best regards
PI-Star Lord