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LM5155: Webench to design a SEPIC led driver

Johnny Vidjeskog
Prodigy 10 points
Part Number: LM5155

When using Webench to design SEPIC leddriver using LM5155 it gives a L(coupled) value of 2.28µH, Excel quick calculator give 22µH, see attachment. VIn=4.5...18V, Vout=9V (led) Which is more reliable? Thanks!

  • 0
    TI__Genius 11215 points

    Hello Johnny,

    Thanks for reaching out. I cannot see your attachment, but I would suggest to check the Bode plot on the Excel quickstart calculator to check whether the converter is stable or not. Anyway, there are some reference designs available on how to drive led with a SEPIC topology : https://www.ti.com/reference-designs/index.html#search?keyword=sepic%20LED 

    Kind regards,

    Elisabetta 

  • 0 in reply to EM
    Prodigy 10 points

    Thanks! Bode plot seems to be quite stable for both e.g. 3µ and 22µ. Efficiency improves with higher L value... I have ordered a SEPIC eval board (here L=1.5µH) so I will try out with this.... BR Johnny

  • +1 in reply to Johnny Vidjeskog
    TI__Genius 11215 points

    Hello Johnny, 

    This sounds good, efficiency is improving because you have less ripple in a big inductor. I will now close this thread then. if you have further questions please post them here or open a new thread if this one is already locked. 

    Kind regards, 

    Elisabetta