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Original question:

UCC2813-5-Q1: FLYBACK CONVERTER

UCC2813-5-Q1: Power management forum

Boggarapu Madhusudan
Prodigy 85 points
Part Number: UCC2813-5-Q1

I took the help of WEBENCH  POWER DESIGNER for design of my Fly back converter of 56 w. My design no. 146.My user Id is info@aeshyd.com.

Another clarification required.  you said NS1 is secondary and NS2 is auxillary.  But the winding resistance information provided in the solution is as following, which quite contradicting. 

Primary resistance RP = 870 mill ohms

NS1 RESISTANCE RS1= 8.6milli ohms

NS2 Reistance RS2 = 700 micro ohms

in the above windings primary current (nominal)   = 2.5 A(approximated), its resistance is 870 milli ohms

                                    secondary current              =4.5A                             its resistance is 8.6 milli ohms

    where as auxillary current is assumed to be a maximm of 250 ma, its winding resistance is 700 micro ohms

       this above information is not justifiable. normally large current winding shall have very  low resistance, so that copper losses will be minimized. the information provided in the solution is contradicting the transformer basics.

Please look in to the matter and clarify.

kindly communicate to email ID madhu75363@gmail.com also.

link for the design is provided:  webench.ti.com/.../SDP.cgi

  • 0
    TI__Prodigy 285 points

    Hi Boggarapu, 

    The transformer recommended in the design is a custom part, meaning that the resistances you see are not of an actual transformer, just mere estimates.

    The winding resistances, and accordingly copper losses, should be accounted for in the actual transformer you select.

    Thanks,

    Mujtaba

  • 0 in reply to Mujtaba Saeed
    Prodigy 85 points

    whether it is estimated or actual transformer, the winding resistance will be according to current carrying capacities and number of turns.  In the refered circuit the winding resistance is more though number turns are less and current capacity is more, hence winding resistance is to be less than low current winding.  This is a basic electrical rule.  If the app is suggesting otherwise then its creation software is to be reviewed.  This kind of recommendations create unnecessary confusions.  People have very high expectations on design suggestions from TI.

  • 0 in reply to Boggarapu Madhusudan
    TI__Prodigy 285 points

    Hi Boggarapu,

    I will look into the matter, and get back to you by early next week.

    Thanks,

    Mujtaba

  • 0 in reply to Mujtaba Saeed
    TI__Intellectual 2630 points

    Hi Madhusudan,

    We understand that for high current application winding resistance should be minimized, for custom transformer (not a actual transformer), these are kind of fixed values. For typical application, these values indicate the maximum value of resistance which we should have in custom transformer to maintain the efficiency.

    Since there is no actual transformer, it will be difficult to estimate these resistances as well (as AWG, Average Length per winding, Strands data is unknown.). We will check with product expert to help in better estimation of these resistances and update the model in future. Let us know if you need any other help ?

    Regards

    Shaheen