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LM5023: Design guide

PieterT
Intellectual 610 points
Part Number: LM5023

Hi Everyone,

I'm struggling a bit to get going with this design, I know webench can be used, although I want to do the design myself, including the transformer design.

I've been going through the datasheet, although I want to know whether a reference design is available that I can use to work with.

My requirements are :

Vin : 14 ~ 50V

Iout = 12V,3A

I need isolation and hoping for light load efficiency

If any other controllers are available with design guides and that meet these specs I'd really appreciate a link as I have only found the lm5023

Thanks in advance for any help

  • 0
    TI__Mastermind 34465 points

    Hello ,

    The data sheet Section 8 and Section 9 page 18 to page 30 has extensive information and  is the primary source of design and application information
    for the LM5023.
    Additionally the LM5023 has an Evaluation Module available with a User Guide detailing a reference design with test results and also
    test waveforms.
    https://www.ti.com/tool/LM5023-2NBEVM

    Regards

    John

  • 0 in reply to John Griffin1
    Intellectual 610 points

    John,

    Thank you for the reply. I completely agree that the datasheet provides extensive information on the design, although in the initial example some assumptions are made:

    • Lp = 400 µH

    • RSENSE = 0.15 Ω

    • VDC(min) = 127 V

    • VDC(max) = 325 V

    • TPROP = 160 ns

    • VCS = 0.5 V

    • NAUX = 10.9

    • NPS = NP/NS = 6

    • tDLY = 580 ns

    I'm not quite sure how this primary inductance and turns ratios are determined. I'm currently reading up on QR flybacks, specifically Exposing the Inner Behavior of a Quasi-Resonant Flyback Converter, to better understand this.

    Thanks again for any help

  • 0 in reply to PieterT
    TI__Mastermind 34465 points

    Pieter,

    The output voltage of a flyback is set by the equation

    Vo = (D/(1-D))*Vin/N

    The turns ratio is selcted so that at low line D is less than 0.5

    In this example Vo = 19.4 v and this sets N = 6.35 max
    Turns ratios less than 6.35 will allow for maximum duty cycles less than 0.5

    The inductance is set by the power rating

    P= 0.5*Lp*Ip^2*f

    You need to choose the switching frequency, f

    Ip is the peak primary current and this set when you choose a transformer core.

    Transformer design is discussed in detail on these seminar papers

    Regards

    John