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Original question:

LM25184-Q1: PSR Flyback 120W DC-DC converter design - Transformer support

LM5185-Q1: 125W Flyback PSR DC-DC converter design review

RAVINDRAN PALANI
Prodigy 90 points
Part Number: LM5185-Q1
Other Parts Discussed in Thread: LM5185

Tool/software:

Hi Team, 

Finally, I have created the schematic 125W Iow cost Isolation design using LM5185PWPR IC. Thanks for Youhao, Eric lee and David suggestions and supports. 

I got support from coil craft for custom transformer design tuns ratio 1:1:0.2, please find the attached specification sheet for your reference. I kindly request you to review the attached updated my schematic and TI flyback calculation sheet. Let me know if any correction and improvisation needed before starting the PCB design. Also, I expected over 90% efficiency in this design what else can do, to improve the efficiency and reduce the power loss in my design. 

Let me know your valuable feedback. 

Thanks. 

Power board Schematic.pdf2146.125W PSR Flyback--LM5185_Design_Updated_29May24.xlsx

  • 0
    TI__Guru* 78060 points

    Hi Ravindran,

    Thank you for reaching out.  First, a friendly reminder that I don't think you can post Coilcraft datasheet due to its confidential marking unless you get their agreement.

    I reviewed your design calculator, and you should select Rcs=4mOhm in order to limit the peak current.  The 4mOhm suggested value already have 10% power margin.  On the other hand, please make sure the transformer does not saturate at 25A peak on the primary winding.  

    You may need to use parallel MOSFETs to handle the 120W. 

    Attached is my review markup. I also recommended different part selections, trying to optimize your BOM cost as well as performance.

    Good luck in your project.

    125W Flyback Review--Power board Schematic (2).pdf

    Regards,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 90 points

    Hi Youhao, 

    Thanks & Good to see your comments/suggestions back. 

    I have updated schematic based on your suggestions.

     

    Do you think the EMI/EMC filter is optional for this Isolated PSR flyback. let me know if any recommended cost-effective noise filters.

    we have small board dimensions for power board & control board which is 100mm x 50mm area, since costing and board layout are challenging, I am prepared some small form fit packages. I have modified the GND connection with reference to LM5185 EVM.

    I can see the transformer primary peak current support up to 30ADC, I believe this is sufficient safety margin for current design update.   

    Regards,

    Ravi  

  • 0 in reply to RAVINDRAN PALANI
    TI__Guru* 78060 points

    Hi Ravi,

    I assume you incorporated my comments.  Your second MOSFETs cause a short.  Please update it as shown below.  the Gate of Q2 needs to connect to R93, but not the drain of Q1.

    Regarding EMI, I would recommend to keep it at least in your prototype, and you can decide whether to use it in your final product.  If you don't want to use the EMI filter, you can uninstall the parts, or eliminated in your final board.

    Good luck!

    Best Regards,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 90 points

    Hi Youhao, 

    Sorry, that is schematic poor net connectivity error, I updated now.

     

    At current, I am working on layout placement, li will reach you, if I have any doubts/help on further. 

    Thank you!  

  • 0 in reply to RAVINDRAN PALANI
    TI__Guru* 78060 points

    It looks good.  You should also update your transformer symbol to remove the non-existing winding between pins 9 and 10.  Otherwise it would cause confusing to others (mainly your colleagues and customers) if they don't have your xfmr datasheet.