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Thread: Resonant SMPS using L6599

  1. #31
    @ Res

    I am not sure if thats the reason for the semi sinusoidal waveform, in my case I have almost perfect sinusoidal wave form at the Cr without connecting any resistors to it (when the SMPS is loaded)


    And thats another evidence that your SMPS is still not running where Fs = Fr, and it requires some perfect tuning.

    Please post some pictures for the output of the SMPS in idle, AC coupling

    Thanks
    Last edited by MicrosiM; 09-09-2019 at 05:03 PM.
    www.diysmps.com & www.Micro-Audio.com

  2. #32
    diysmps Member
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    For LLC it's not mandatory to work at Fs = Fr only.
    Below Fr it's a boost gain zone and above a buck gain.
    Below Fr must check to not enter in capacitive mode (current lead voltage), losing ZVS with risks for MOSFETs.

  3. #33
    Quote Originally Posted by iop95 View Post
    For LLC it's not mandatory to work at Fs = Fr only.
    Below Fr it's a boost gain zone and above a buck gain.
    Below Fr must check to not enter in capacitive mode (current lead voltage), losing ZVS with risks for MOSFETs.

    Yes, that makes sense, but optimal point where Fs = Fr, thats my own opinion.

    Thanks
    www.diysmps.com & www.Micro-Audio.com

  4. #34
    diysmps Senior Member res_smps's Avatar
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    the higher resonant frequency of my smps is 68kHz and the lower is around 30khz.
    my smps works with 50khz to 90khz variable switching frequency

    @microsim
    sorry I'm out of town now can't do the test

    @iop95
    Do you have a method to check whether my smps is entering capacitive mode or not?

    although my smps is good in load testing, I admit my smps is still not perfect, there are some things that still need to be fixed and improved :
    - regulation with no load is still not smooth
    - idle temperature of the transformer reaches 60C (30 minutes test)
    - at heavy loads the resonant capacitor is very hot

  5. #35
    diysmps Member
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    @res_smps
    There are some calculations to check for entering in capacitive mode; I have a spreadsheet but need to translate in english... maybe in next days I can upload it.
    - LLC is difficult to controll... transfer function is complex and have some non-linear elements, so may exhibit control problems at light loads/no load especially
    - check core loses vs temperature... most of them have a minimum around 80-100C, so 60C may be not so bad if other requirments are not violated.
    - need to check esr capacitor and current supported at working frequency range; may need to use more parallel/series caps to remain below limits and reduce cap losses (esr * Irms^2)

  6. #36
    @Res

    That means your SMPS is not running properly, and I believe that you still have a lot of work to do.

    Good luck
    www.diysmps.com & www.Micro-Audio.com

  7. #37
    diysmps Senior Member res_smps's Avatar
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    Quote Originally Posted by MicrosiM View Post
    @Res

    That means your SMPS is not running properly, and I believe that you still have a lot of work to do.

    Good luck
    It's okay, I will try to fix and improve one by one
    I do this just for fun, not being chased by any target

  8. #38
    diysmps Senior Member res_smps's Avatar
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    this is the waveform, i measured it using pcb V1 (post # 1)
    https://drive.google.com/drive/folde...BP-v_4cYAZewmD
    my oscilloscope is only dc coupling, so i added 100n capacitor in series with the probe
    1. Vout with AC coupling, regulated, no load
    2. VCresonant (Vcr), regulated, no load
    3. Vcr, unregulated, no load, 100khz switching freq
    4. Vout with AC coupling, unregulated, no load, 100khz switching freq
    5. vcr, unregulated 69khz no load
    6. vcr, unregulated 69khz 100 ohm load
    7. vcr, unregulated 61khz no load vcr
    8. vcr, unregulated 61khz 100 ohm load

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