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Original question:

UC3845A: Primary inductance of Flyback Transformer

LM5156: Power management forum

Faheem Minhas
Prodigy 40 points
Part Number: LM5156

Flyback topology

CCM mode

What are the effects of percentage of ripple current ratio. As the manual says its a good starting to choose it as 30% to 70% maximum. What are the effects if it 100% or more than that. The transformer can hold the peak current. Will it cause EMI issue or any similar issues. Moreover is there any equivalent flyback converter controllers in CCM and DCM. For example UCC2805QDRQ1. Moreover please also provide the quick start calculator for UCC2805QDRQ1.

Thanks.

  • 0
    TI__Genius 13075 points

    Hello,

    Thanks for reaching out. Usually with a higher ripple you might see worse EMI, external components has to be sized for bigger peaks and higher power dissipation. With a ripple of 100% you are already in transition mode. Could you please clearify what you mean with 'Moreover is there any equivalent flyback converter controllers in CCM and DCM. For example UCC2805QDRQ1''?

    Best regards,

    Moritz

  • 0 in reply to Moritz
    Prodigy 40 points

    Thanks for your reply. The output power changes for LM5156 that shows everything OK on efficiency but the ripple current ratio goes from25% up to 95%. Its OK for the parts as they can still deal with the current. Will it still cause worst effects on EMI/EMC and difficult to get certification.

  • 0 in reply to Faheem Minhas
    TI__Genius 13075 points

    Hello,

    Thanks for the response. The ripple current ratio has not that much influence on the EMI. Most important is to do a good layout first. For that, please follow the layout guidelines provided in the datasheet.

    Best regards,

    Moritz