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Thread: Resonant power supply

  1. #1
    diysmps Member
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    Resonant power supply

    What do you think about those power supplies, ZCS in particular ?
    Did someone try one ? If so, please share with us your experience
    Any sugestion is apreciated

  2. #2
    diysmps Member
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    I know this kind of power supply are more difficult than hard switching
    In my testings the current flowing in primary transformer (ETD49) when i connect a load in secondary side, looks like this

    With no load, the current looks like this in the primary side

    While the current looks like those picture above, the voltage looks like this

    I manage to get same results even without L-series. Primary winding is side by side with secondary winding like in this picture

    What i like most in this case is that the capacitive coupling between primary and secondary windings is verry low or not at all. In this case secondary side is more ''clean''
    The disatvantage is that you need a little more space for windings in this case

    Schematic Diagram resonant.pdf
    Last edited by maxente; 04-14-2017 at 08:11 PM.

  3. #3
    .... Silvio's Avatar
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    Hello I am not really sure of this but the circuit you are using is for a hard switched half bridge smps. To get a resonant circuit it takes more than that. The smps shifts off resonance with different load on the secondary, however the circuit has to adjust the resonant frequency to maintain it. The circuit you are using is not suitable for what you are trying to achieve. I suggest you read more about the subject ZVS and resonant smps.

    Good luck

    Silvio

  4. #4
    kees57
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    Maybe you have some ideas about this, special the feedback because here are different possibillities, and need to see
    if the inverter do work fine when with mig I do switch on and of randomly while weld thin metal like a car.

    regards

    ScreenHunter_75 Apr. 26 11.56.jpg

    ScreenHunter_70 Apr. 25 20.46.jpg

    ScreenHunter_73 Apr. 26 11.53.jpg

  5. #5
    diysmps Member
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    @Silvio, let me show you some more picture
    What you see below is one channel (yellow) of scope conected to the primary ETD49 trafo and second channel (purple) is monitoring current flowing thru primary of ETD49. First picture is with no load, second and third is with 200w load connected in secondary of ETD49

    I tested even with 1kw load and the current is maintaining the shape you are seeing in pict 2 and 3
    So @Silvio, what do you make of this, still believe is hard switching ?

  6. #6
    .... Silvio's Avatar
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    Quote Originally Posted by maxente View Post
    @Silvio, let me show you some more picture
    What you see below is one channel (yellow) of scope conected to the primary ETD49 trafo and second channel (purple) is monitoring current flowing thru primary of ETD49. First picture is with no load, second and third is with 200w load connected in secondary of ETD49

    I tested even with 1kw load and the current is maintaining the shape you are seeing in pict 2 and 3
    So @Silvio, what do you make of this, still believe is hard switching ?
    Hi Maxenete, Yes I can see that the current has a nice sine wave but I believe that the VOLTAGE curve should be somewhat the same. The current curve looks like it is charging a bank of capacitors and softly charging and discharging hence the sine wave. The switching transistor has to be soft switched at the zero voltage point otherwise it will never get the shape of a sine wave. Special chips are made for this purpose. The frequency of the chip will shift a little up or down to maintain the resonant frequency according to the load imposed on the tuned circuit. These type of resonant smps tend to get a little complicated and you have to understand the function of the whole set up. Your circuit is not made for a resonant circuit.

    The leakage inductance you created in the transformer helps to get a little roundness but then you have to tailor a capacitor in the output to get to resonance. Then again when you load the smps it will shift off and loose resonance. Your wave shape will change again.

    I once made a DC to AC inverter running from a car battery. It had a normal iron core, I made a series choke in the center tap of the primary as it was a push pull circuit and then I tuned the output voltage with a parallel capacitor across the secondary winding. I got a very nice sine wave but when I started loading the inverter it went off resonance. What I am trying to tell you is that it is not so simple as you think.

    I hope that helps

    Silvio

  7. #7
    diysmps Member
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    Yeah, perhaps a more appropriate term should be soft switching power supply and not resonant. Maybe a mod or admin should change the name of the thread in Soft switching power supply
    I disconnect the probe from primary ETD49 and conencted paralel to capacitor in series with primary winding
    First picture is with no load
    Last edited by maxente; 05-09-2017 at 08:35 PM.

  8. #8
    .... Silvio's Avatar
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    Quote Originally Posted by maxente View Post
    Yeah, perhaps a more appropriate term should be soft switching power supply and not resonant. Maybe a mod or admin should change the name of the thread in Soft switching power supply
    I disconnect the probe from primary ETD49 and conencted paralel to capacitor in series with primary winding
    First picture is with no load
    If you really want to see what is your wave shape measure across the primary winding. SEE THAT YOU HAVE ISOLATION TRANSFORMER ON OSCILLOSCOPE OR SMPS as you may burn your oscilloscope if it is not isolated

  9. #9
    diysmps Member
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    I just toldy in post #5 the voltage across primary winding is with osciloscope connected directly to it with x100 probe. The same is with voltage across capacitor in series with primary winding.
    The osciloscope is powered with a separator trafo.

  10. #10
    In Post #5, pictures 2 & 3, it appears that your supply is running at near ZCS(zero current switching). The voltage is switched while zero current is flowing in these systems and your supply is close to that. It is definitely switching softer than a traditional hard switched supply, although full ZCS isn't achieved.

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