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LM5017 CURRENT DISTRIBUTION OVER PRIMARY AND SECONDARY

vipin mishra
Intellectual 270 points
Other Parts Discussed in Thread: LM5017

Dear sir,

We are using the LM5017 reference design for isolating the input and output .But output current  present at the secondary of Transformer is very less and it is only 200 MA but i need to update the secondary side of transformer up to 400-500 MA .

Can you please suggest is there any way how can i variate the current flowing between Primary and Secondary.

 

I want to make 9.5V output of 400 ma atleast.

 

  • 0
    TI__Expert 7395 points
    Vipin,

    Thanks for your interest in TI here. I've contacted the relevant product group. You should hear from them soon.

    Can you explain specifically what LM5017 reference design you are using? Have you made any changes to that design?

    Regards,
    John
  • 0 in reply to John Stevens
    Intellectual 270 points
    Dear sir,

    Please find the link below which i am using currently .
    www.ti.com/.../snva611b.pdf

    I have not changed anything from this design till now .

    But i want to change it based on my application.

    isolated (secondary -400ma),

    Regards,
    Vipin
  • 0 in reply to vipin mishra
    TI__Intellectual 2320 points

    Hello Vipin,

    I have noticed in your application schematic that the minimum VIN can go down to 12V. In a Fly-Buck topology, we recommend limiting the minimum VIN value to at least 2 times the VOUT primary in order to maintain the secondary side regulation. That's why you can see why we have limited the VIN min in the application note to 20V. A value of VIN more than 2 times the VOUT, primary (in Fly-buck) means a lesser off-time period available to charge the secondary output capacitors and hence maintain regulation.

    That being said, are you planning to load the primary side output as well? Please note that the sat rating of this coupled inductor is 0.67A and the min current limit of the part is 0.7A. The total load (secondary + primary) must be less than the 0.6A or so without triggering the peak current limit of the part or/and saturating the coupled inductor. However, with the EVM you should still be able to draw at least 400mA from the secondary side (provided you keep the primary unloaded).

    Regards,

    Sourav

  • 0 in reply to Sourav.Sen
    Intellectual 270 points

    Hi Saurav,

    Thanks for quick reply sir.

    Can you suggest weather can i get better regulation at the secondary output of LM5017 by changing the inductor or capacitor present in the evaluation board for the input of 14V-75V.

    Regarding the secondary output current we are not going to use much the primary output (10V output) so as you suggested i can get upto 400MA at the secondary output.

    Regards,

    Vipin

  • 0 in reply to vipin mishra
    Intellectual 270 points

    Dear sir,

     

    We are going to build the above evaluation board circuit for atleast 400MA for the input range of 14V-75V .

    Can we achieve using this circuit or we need to modify something in circuit.

    Regards,

    Vipin

     

  • 0 in reply to vipin mishra
    TI__Intellectual 2320 points

    Hello Vipin,

    As I had posted earlier, please ensure that the VOUT,pri is atleast around 7V (half of min VIN) in order to make sure you can regulate the secondary side well. If you increase the VOUT pri, your secondary side regulation will suffer. You in that case will need to use a coupled inductor with a turns ratio of 1:1.5 (Np:Ns) for the part to work accordingly. You can also check the LPD8035V series for the coupled inductor.

    This entire concept is based on the idea that you will need to regulated output on the secondary side at VIN =14V. If you do not need a that specific regulation requirement at the lowest VIN, you can pull up the VOUT(pri) to 10V, but you will need to check for regulation on the secondary side at the lowest VIN.

    Regards,

    Sourav

  • 0 in reply to vipin mishra
    Intellectual 270 points

    Dear sir,

    I am using the same configuration with LPD5030 as a transformer but i am getting different result for the above mentioned schematics.

    1 WHEN VIN =20, J18=10V,J19=10V

    2 WHEN VIN=25, J18=10V,J19=15V

    3 WHEN VIN=30, J18=10V,J19=20V

    4 WHEN VIN=35,J18=10V,J19=25V

    This result is same observed on all the three Board.LPD5030 was 1:1 Transformer but i am getting VOUT distributed between J19 and J18.while J18 being fixed and other is varying.

    kindly suggest for this i have posted schematics already in the above post ,Please take this as a refrence. BATTERY GROUND is shorted with NON ISOLATED GROUND and ISOLTED GROUND is connected as shown in the schematics.

    Regards,

    Vipin