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Original question:

LM5160-Q1: Boot resister of LM5160-Q1

LM5160-Q1: LM5160-Q1

AJAY CHOLE
Prodigy 210 points
Part Number: LM5160-Q1
Other Parts Discussed in Thread: LM5160

Hi. I want a 12V, 1A isolated output through the utilization of LM5160-Q1 in Fly-buck converter mode. The Vin range is 19 to 26V. I do not want to use the primary (non-isolated output) of the Fly-buck converter. Can I keep the primary output OPEN? Thanks

  • 0
    TI__Mastermind 33050 points
    Hello Ajay,

    Yes, this is feasible. Just have feedback resistor divider and output capacitor from Vout to Gnd (pri).

    Hope this helps?
  • 0 in reply to David Baba
    Prodigy 210 points

    Hi. Thanks David. I have tried to design the Fly-buck converter using Webench (first time user), design report attached. A custom transformer is recommended. The transformer i.e coupled inductor specification is Lp= 50.063 µH, Rp= 71.0 mOhm, Leakage_L= 1.502 µH, Ns1toNp= 1.578, Rs1= 211.0 mOhm. I am not able to understand these specs. Lp is magnetizing inductance?Rp is resistance of magnetizing branch? Ns1 to Np is turns ratio that is Ok! What is Rs1? Also the current rating/power rating of the coupled inductor transformer is not given in the design report. Is there any way to pre-select an easily available coupled inductor from Coilcraft/Wurth Electronics etc and may be adjust the duty ratio/on-time to get the desired isolated output (12V in this case?). What can be done? Can you suggest a better design using easily available coupled inductor?Thanks and Regards, Ajay CholeWBDesign2.pdf

  • 0 in reply to AJAY CHOLE
    TI__Mastermind 33050 points
    Hello Ajay,

    LP = Primary inductance
    Rp = Resistance of the Primary Winding.
    Rs1 = Resistance of the secondary winding.

    Set the Isat = to the Max peak current limit of the LM5160 which is set to ~2.875A.

    In answer to your question, yes, you can use a 1:1 set the output voltage to ~12.5V and use a 1:1 turns ratio. Your load regulation may suffer a little at full load and Vin min.

    Hope this helps.
  • 0 in reply to David Baba
    Prodigy 210 points

    Thank you David. I will try setting 1:1 ratio.

  • 0 in reply to David Baba
    Prodigy 210 points
    Hi David. Thanks. When there is no-load connected at the primary-output then the average current through the primary inductor will be zero right? At steady state how the current through primary and secondary will look like? Please help.
  • 0 in reply to AJAY CHOLE
    TI__Mastermind 33050 points
    Hello Ajay,

    With zero load currents the inductor current will be triangular about 0A.

    Hope this helps?
  • 0 in reply to David Baba
    Prodigy 210 points

    Thanks David. I will try to simulate the circuit and check the performance before implementation. Thanks and Regards, Ajay Chole