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UC3842: UC3842 Transfer Function

Werner Verschuur
Prodigy 40 points
Part Number: UC3842

Hi,

I need help converting a UC3842 in Flyback application Transfer Function from Plant H(s) and Closed Loop G(s) to h(t) and g(t) to do Bode Plots of Gain and determine crossover frequency.

H(s) = Fgo*(1 + (s/Wesrz)) * (1 - (s/Wrhpz)) / (1 + s/Wp1) * (1 / (1 + (s/(Wp2 * Qp)) + (s^2/Wp2^2)))

I would assume we need to convert via Reverse Laplace Transforms? 

It would be great to see the steps of the conversion!!!

Thanks,

Werner.

  • 0
    TI__Mastermind 34465 points

    Hello Werner,

    Attached is an excellent document on compensation of switch mode power supplies.

    There is a section on current mode flyback converters that will help you with generating the Bode plots5706.COMPENSATION.pdf

    Regards

    John

  • 0 in reply to John Griffin1
    Prodigy 40 points

    Hi John

    Thanks, it's a nice document but it's not what I need.

    I have written a design tool for the UC3842 "added flexibility" to speed-up my designs that require Isolated PSU's.

    I would like to plot the Gain Margin by using the Transfer Functions, but I can't find any info on how to convert the H(s) terms to h(t) which is needed for Bode Gain Plot

    Below is a screenshot of the program, you can see the Gain Plot is wrong but the Phase is correct.

    Need a Mathematician  

  • 0 in reply to Werner Verschuur
    TI__Mastermind 34465 points

    Hi Werner,

    Excellent.
    Let me know how you get on.
    Sorry I was unable to help.

    Regards

    John

  • 0 in reply to John Griffin1
    TI__Mastermind 31580 points

    Hi Werner,

    The UCC28C4x datasheet,

    http://www.ti.com/lit/ds/symlink/ucc28c45.pdf

    has a very detailed section on the control loop design, it may help you.

    Regards

    Peter

  • 0 in reply to Peter Meaney
    Prodigy 40 points

    Hi Peter

    Thank you very much it does deal with Control Loop Design, it however does not show how to convert the H(s) and Gtotal(s) terms to h(t) and g(t) to draw the plot.

    Below is an example of such a conversion on the first term.

    I was hoping one of your customers previously requested this converted formula and you could merely pass it on. Seems no one is interested in manually doing the plot..

    Keep this thread open, I am working on a solution as I get time and will post updates. Surely every designer should be able to do this plot.

    Regards,

    Werner.