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How to reduce the input current in Class-E DC-DC converters

Discussion in 'Circuit Simulation & PCB Design' started by mady, Jul 22, 2015.

  1. mady

    mady Member

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    The specifications of the circuit is Vin=60V, Fsw=5Mhz, Vout=15V, Pout=16W. I am getting the Vout is 18V, Iout is 1.2A and Iin is 0.980A. So, If I reduce the input current I will get the high efficiency of the circuit. So, please suggest me what I suppose to do in order to reduce the input current of the circuit.

    Here, I have attached the circuit schematic and waveforms.
     

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  2. ronv

    ronv Well-Known Member Most Helpful Member

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    I'm not sure where you find one, but you need a faster FET. Almost all the losses are switching losses there with just a little in the diodes.
     
  3. mady

    mady Member

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    Please suggest me that the faster FET which has to with stand with above 300Vds, high frequencies and also it has low Rds(on) and less gate charge...
    And also, how to reduce the switching losses... what I have to do....
     
  4. dave

    Dave New Member

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  5. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    5mhz seems fast. You are running resonant mode. It that what you want to do?
    400 volts on the MOSFET is high for 60V in. Lower voltage MOSFETs will run faster.
     
  6. ronv

    ronv Well-Known Member Most Helpful Member

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    Hi Ron,
    From another place - he wants a zero voltage switch resonant converter. Math gives me a head ache. :banghead:
    PS.
    I'm coming out your way to visit my kids, could you turn off the rain for a while?
     
  7. analog1

    analog1 Member

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    The efficiency is poor I agree. Why 5 MHz that is kind of hi, Capacitors start behaving like coils at those frequencies so there are going to get losses there. If I was to design this thing 200kc will be more appropiate
     
  8. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    Ron, Give me your credit card and I will take the kids out to Olive Garden. Save you a trip. LOL
    Mady, I think the power supply is not doing what you think it should.
    Please show Vpri and Vsec.
     
  9. mady

    mady Member

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    Here, I have attached the Vpri and Vsec waveforms and also check that define windings. What ever I have defining the windings is write or wrong? I am working on 4:1 step-down transformer. If I understand is correctly, If the primary voltage 60V and the secondary is 15V.
     

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  10. ronv

    ronv Well-Known Member Most Helpful Member

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    It sounded like a plan to me but the wife killed it. :oops:
     
  11. mady

    mady Member

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    My task is to design the circuit with that much high frequencies and in orer to get the higher efficiencies like (~90%).
    As far now, The results of the circuit is Vout = 16.225, Iout = 1.154 and Vin = 60, Iin = 0.441. So, the efficiency is 70%
    If I decrease the input current to 0.350m with out changes in the output voltage and current, then the efficiency is more high.
    So, how to do this in the circuit ?
     
    Last edited: Jul 26, 2015
  12. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    Question: Is the square wave in to the gate of the MOSFET the 5MHz?
    OR
    Is the resonant frequency of the LC on the D of the MOSFET set to 5mhz?

    When a resonant power supply is described it is often not clear what frequency.
     
  13. mady

    mady Member

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    The gate of the MOSFET is 5MHz switching frequency.
     
  14. ronv

    ronv Well-Known Member Most Helpful Member

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    mady
    You can adjust the size of your L2 so that the phase is correct for zero voltage switching at 5 Mhz.
    I didn't have your exact FET in my library but tried it with 2 others and was able to get into the high 90's.
    Here is an example with 40 watts out and 41.2 watts in.
     

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  15. mady

    mady Member

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    I have few questions, what type of core material of the transformer you have been used ?. what is the coupling factor, Area of cross section Ae, effective magnetic length 'le', Effective permeability of the core 'Ue' which you have been used?
    And also provide me the MOSFET model? the one which you are shown in the circuit is not available in the market and also hard to find the data sheet for that.....
    As you said, I have changed the L2 value, then the efficiency of the circuit is 28% and the phase is not correct for Zero Voltage Switching at 5Mhz.
     
    Last edited: Jul 27, 2015
  16. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    Mady,
    You need to choose a C1 that can handle large current. (also L1, L2) If you are really going to build it they you need to pick parts you can get. Not 69.2pF but 68pF. Spend some time reading Wima Capacitor Design Notes.
    Where did you get the design?

    RonV,
    Why C4, C5 in the first schematic? They seem wrong. I can see primary to secondary caps but not there.
     
    Last edited: Jul 27, 2015
  17. ronv

    ronv Well-Known Member Most Helpful Member

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    Well, we both have the same problem. :banghead: I don't have your FET. But yours should be better.
    You need to experiment with the inductor to match your FET. It may need to be higher or lower. than mine.
    When I went to school buck converters were just being invented so you probably need someone with more recent experience.:D
    If your task is to actually build this you have a lot of hard work ahead.
    You might find a planar transformer that will work at 5 Mhz.
     
    Last edited: Jul 27, 2015
  18. mady

    mady Member

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    You mean that C1 = 68p and L1 = 17u. I have changed those values but the efficiency is too low.

    I have designed by following the IEEE papers.
     
  19. ronv

    ronv Well-Known Member Most Helpful Member

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    Download LTSpice from the web - it's free. Then you will have the FET.
    Once you have done that you can run this file to see results.
    I don't see any inductance values for the transformer in your schematic. Maybe that is the problem.
     

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  20. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    It appears to me that DC current is saturating the core with rising load current.

    I would expect some means of cancelling DC current with a full bridge or 3rd winding.
     
  21. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    ronv,
    Look at the S-D voltage on M1. You exceeded the voltage of the MOSFET. Very much excedded.
    Tony,
    There is no DC on the core.
     

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