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LM5023: Two switch flyback

toktam khani
Prodigy 90 points
Part Number: LM5023

Hi there,

 i wanted to use LM5023 for non-isolated two-switch flyback. i have some questions:

- i wanted to use Webench for calculations but it won't work. Vin: 600 - 1500V; Vout: 24V & Iout: 1A.

- generally, do you suggest this IC for 2-Switch topology?

- I need non-isolated; can i use this IC for that? if yes, how would be the feedback configuration? 

Best Regards

Toktam

  • 0
    TI__Mastermind 21335 points

    Toktam,

    2-switch flyback is not such a popular topology and this is why you don't see it in Webench. You can analyze the 2-switch flyback power stage using TI Power Stage Designer. The small signal analysis is the same as for any 1-swicth DCM or CCM flyback. And you can use any off-line flyback PWM or general purpose PWM controller to control the 2-switch flyback power stage. The only issue is developing a high-side gate drive from the PWM signal but the timing between high-side and low-side gate drives is not critical. Any mismatch between gate drive signals will simply mean a reduction in max duty cycle and not a risk of shoot-through like what we have in half-bridge topologies.

    I understand the benefits you are hoping for using the 2-switch flyback topology with 600V<VIN<1.5kV. You might also consider using a traditional 1-switch flyback with a SiC as the main MOSFET. TI has recently introduced UCC28C56H devices that have UVLO options uniquely tailored for SiC application such as what you are describing. The growing popularity and many choices of SiC/controllers/drivers have allowed the traditional 1-switch flyback to operate effectively from much higher input voltage, making the 2-switch flyback less popular.

    Regards,

    Steve

  • 0 in reply to Steven Mappus1
    Prodigy 90 points

    Hi Steve,

    thanks for the answer, it is good to know that the gate signal mismatch won't cause a big problem.

    simulation is not a problem for me as i already done it in LTSPICE and it works fine. to tell the truth, the datasheet of LM5023 is not that much clear(or to say user friendly) on calculating components theoretically and it is a little bit confusing for me. i wanted to see what are the components selection in Webench in the case of normal single switch flyback but with mentioned parameter i only got the massage that the "design can not be created. your preferred device does not work with the input you selected"

    BR Toktam

  • +1 in reply to toktam khani
    TI__Mastermind 19825 points

    Hi Toktam,

    Steve is out a couple of days due to thanks giving.

    Sorry that you were not able to have webench model. But we do have PSPICE model for UCC28C56 in the product folder ready to download for the single switch flyback option.

    https://www.ti.com/product/UCC28C56H-Q1#design-tools-simulation

    I too verified the option in webench with LM5023 but it says the same error message, so we eed to go by datasheet equations or the simulation model provided and try to modify it.

    https://www.ti.com/product/LM5023#design-tools-simulation

    Please let us know if you have any questions.

    Regards,

    Harish