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Original question:

LM2585: Transformer for the LM2585?

LM2585: Transformer ratio for Boost application

vijay Raghavan
Prodigy 60 points
Part Number: LM2585

Hi,

I plan to use LM2585 to convert input 24V to 300V. In WE bench I have got the simulation results which is shown below. I have a query regarding transformer ratio.

In the BOM the transformer specification is mentioned as below:

Ns1toNp: 10   Lp: 485.11 µH  Leakage_L: 9.7 µH  

Does this mean secondary turns is less than primary turns by a factor of 10? 

since this is a boost application, the secondary turns must be higher than primary turns right. 

Please let me know if I am right.

  • +1
    TI__Genius 14415 points

    Hello Vijan,

    Thanks for reaching out to us via e2e.

    You are right, the number of the output windings has to be 10x the number of input windings.

    And I agree that this notation can be misleading.
    You could have multiple secondary windings, e.g. for different output voltages.
    Therefore, the outputs are numbered: secondary #1 (s1), secondary #2 (s2), ...
    So, this notation means:
    number of windings for secondary #1 to number of windings for primary: 10

    Please be careful with the orientation of the output winding, to connect the diode to the correct terminal of the transformer.

    Best regards
    Harry

  • 0 in reply to Harry Hofner
    Prodigy 60 points

    Hi Harry,

    Thank you for the detailed explanation. This sure helps :) 

    Best regards
    Vijay