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Thread: regulated TL494 based SMPS

  1. #1
    diysmps Senior Member res_smps's Avatar
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    regulated TL494 based SMPS

    Dear all,

    is there anyone interested in SMPS using TL494?
    i am developing a SMPS using TL494 (because cheap and easy to find here), but i don't have enough time improving it
    - it is regulated, TL494 placed on primary side, with GDT to drive mosfet (because i found so many counterfeit IR2110 here so i choose GDT)
    - isolation using optocoupler, not GDT
    - no additional auxiliary supply for TL494
    - EPC4649S core for main transformer

    this is my progress so far :
    regulated +-45V, (using TL431 as error amplifier, not just a zenner)
    down to 44,9V in 200W load
    down to 43,6V in 380W load

    i will attach schematic and picture, and simulation files later

    terima kasih,
    res

  2. #2
    diysmps Senior Member res_smps's Avatar
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    schematic V1

    TL494.pdf
    i will explain later

  3. #3
    diysmps Senior Member res_smps's Avatar
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    schematic V2

    reserved for schematic v2

  4. #4
    diysmps Senior Member res_smps's Avatar
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    why I cannot edit or delete my previous post?
    for schematic in post #2
    without no load output voltage is Vzener+2v
    with load connected output is Vzener

    for GDT I use toroid core for EMI filter, with 2mH primary inductance (21 turn)
    GDT winding 1:1:1
    Attached Images Attached Images
    Last edited by res_smps; 06-03-2015 at 10:10 PM.

  5. #5
    diysmps Senior Member
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    You can only edit a post up to 30 minutes after posting it.

    The schematic looks mostly reasonable. A couple of things I would have done differently. A few notes:

    Normally I'd say not to use the TL494, but I understand where you're coming from.

    R42 voids your isolation. You'll have to remove that, I assume it's there for prototyping only, it shouldn't be doing much anyway. Also in terms of isolation I hope you wound the transformer with properly rated tape and margins, that your PCB has a sufficient creepage distance between primary and secondary and that capacitor C35 is class Y.

    Have you stabilised this? I don't see any proper compensation on the schematic to do so. I noted the simulation you put in another thread was oscillating and I think I gave some tips there about it. You're only regulating the positive rail and the negative is only regulated by the linked inductor. That's fine though, just be aware the regulation on the negative rail won't be quite as good.

    The coupling capacitor C14 for the GDT primary is probably not necessary. Don't use it if you don't have to, it introduces a potential resonance between itself and the magnetising inductance of the GDT primary which has to be damped which increases the impedance of the driver which slows switching. R14 is similarly of questionable necessity. Try with and without on your prototype.

    The C18/R31 snubber. Snubbers tend to only really work when both R and C are close to the ideal value. I hope you've calculated or prototyped to get the right value and not just copy and paste it from another design. RC snubbers burn quite a lot of power (P=f.C.V^2) It's presumably there to damp the resonance between Q1 or Q2's parasitic capacitance and the transformer's leakage inductance, although I'm not sure it's in the right place to do so, it should be in parallel with the capacitance. Please feel free to explain it to me. I might just be having a daft moment.

    Regards,
    Matt
    Buck derived converters in regulated power supplies require output inductors
    and the following control modes (voltage or current mode control; bold is recommended).

    Buck (CMC/VMC) | Forward (CMC/VMC) | 2-switch forward (CMC/VMC) | Half Bridge (VMC) | Push-pull (CMC) | Full Bridge (CMC). Click for basic schematics.
    ON Semiconductor TL431 design guide

  6. #6
    KX36

    Could You explain me one thing please. I am going to do some regulated smps based on sg2525, and I do not know wihich way to choose for fedback.
    Plan A
    Secondary --> zener network + resistor + optocoupler
    SG2525 side--> error amp used + compensation

    Plan B
    Secondary --> type II or III compensator based on LT431
    SG2525 --> pulling COMP pin no 9 to GND with optocoupler.


    Thanks for any information.



    res_smps

    I see You are not using the internal errror amps of tl494, tell me please how pulling COMP pin is doing the job at the dynamic loads ? Have you made any tests ? I am curious because I am prototyping my first regulated smps and have huge lack of knowledge.

    Regards

  7. #7
    diysmps Senior Member res_smps's Avatar
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    Quote Originally Posted by borysgo2 View Post

    res_smps

    I see You are not using the internal errror amps of tl494, tell me please how pulling COMP pin is doing the job at the dynamic loads ? Have you made any tests ? I am curious because I am prototyping my first regulated smps and have huge lack of knowledge.

    Regards

    hi borysgo2,
    I never got success using error amplifier and optocoupler (Tl494 on primary side), audible noise came out from transformer.
    many commercial smps i have seen always put tl494 on secondary side without optocoupler

    yes, i have made prototype (post#4)

    then I found this link http://www.trifolium.de/netzteil/kap8.html
    and adopt it to my circuit

    please check my simulationTL494sim.zip

  8. #8
    Thanks !!
    I have made a driver board prototype with SG very similar like from link above and it seem to work OK by pulling COMP pin to regulate PWM.
    For now I will have to finish up universal smps prototype from rubbish parts.

    Regards

    s2.jpg
    s1.jpg

  9. #9
    res_smps

    Could You post Mylib file for LTspice please ??


    Thanks Peter

  10. #10
    diysmps Senior Member res_smps's Avatar
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    Quote Originally Posted by borysgo2 View Post
    res_smps

    Could You post Mylib file for LTspice please ??


    Thanks Peter
    hi borysgo2

    please check this Mylib.zip

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