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WEBENCH® Tools/LM5022: Isolated DC-DC Converter with LM5022

Josh Noble
Prodigy 50 points
Part Number: LM5022
Other Parts Discussed in Thread: PMP20588, TL431

Tool/software: WEBENCH® Design Tools

I need to design an isolated flyback converter with the following requirements:

Nominal Input voltage: 24V

Output voltage: 48V

Max Output Current: 0.6A

I have this webench design passed to me from another engineer => The problem is I don't know what parameters were used in generating this design and haven't been able to find any information detailing how it works (i.e. what resistor would I change to control the output voltage). Is there is any information available that might be useful in verifying this design for my application? Otherwise I will likely have to scrap this one and generate a new design altogether.

Thanks,

Josh

  • 0
    TI__Guru* 78170 points
    Hi,

    Thank you for considering the LM5022 for your application. You can go to LM5022 product page of TI.com, and on the right side of the webpage you will see the Wenbench tool. You select flyback in the "product option" pull-down manu, and input your VIN, VOUT and IOUT parameters, then click "Open Design", you will get a customed design for your application.

    Thanks,
    Youhao Xi, Applications Engineering
  • 0 in reply to Youhao Xi
    Prodigy 50 points
    Once I generate a design where can I find more information on that design? Each of the designs I generate list the flyback transformer as "custom", but for our application we will likely want to leverage a standard component. We need more information (i.e. the relationship between Vout and Rfbt) that would enable us to tweak the design for our needs.
  • 0 in reply to Josh Noble
    Prodigy 50 points

    To add to that, let's say we were to use Coilcraft PA6582-AL as our isolation transformer for example. Its designed for PMP20588 and rated for 54V output. How would we alter the design to generate a 48V output instead of 54V output?

  • 0 in reply to Josh Noble
    TI__Guru* 78170 points

    Hi Josh,

    You are right that you can tweak a webench design for your real application needs. Basically you should contact the magnetics vendor and ask them to provide you a proper flyback transformer.  A proper design is always the results of iterations and trade-offs.  Once you obtained a transformer, is not exactly the same as your initial design, you need to readjust the other components.

    Regarding the Coilcraft transformer, you can change the feedback resistor R25 or R26 or both of the PMP20588 to get 48V output.

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 50 points

    Is there an equation that relates Vout to R25 & R26? How do I determine what resistor values are needed to generate a 48V output?

  • 0 in reply to Josh Noble
    TI__Guru* 78170 points

    Hi  Josh,

    Vout is set by the resistor ratio of R21 to R25//R26.  They should be selected such that when Vout is at your desired set point, the voltage across R25//R26 should equal to the TL431's reference voltage.  If you are not familiar with TL431, please study the datasheet.  

    Thanks,

    Youhao