impedance matching forward converter

Discussion in 'General Electronics Chat' started by philm01, Nov 29, 2014.

  1. philm01

    Thread Starter Member

    Mar 22, 2014
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    Hello everyone,

    I have a quick question regarding impedance matching on a forward converter. Since it is a DC switching transformer, I wasn't sure if whether or not impedance matching techniques were the same as an AC transformer.

    Mainly, how do I impedance match a load on a forward converter?
     
    Last edited: Dec 1, 2014
  2. Papabravo

    Expert

    Feb 24, 2006
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    DC switching Transformer is a bit of an oxymoron. By taking a DC voltage and running it through a switching mechanism you are making an AC waveform. You run AC waveforms of any description through a transformer and you get some kind of output. The transformer doesn't care if it is a sinewave, squarewave, triangle wave, sawtooth or whtever. For most power circuits I can't imagine what the usefulness of impedance matching might be. Perhaps you can give us a schematic so we can verify either hypothesis.
     
  3. philm01

    Thread Starter Member

    Mar 22, 2014
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    0
    Yes, I will provide one. I know that for impedance matching, we do this so that the most amount of power is delivered to the load. Which, is what I need to do for my Rl on the secondary but I am working with high voltage.

    Attached is a schematic for my circuit. Please excuse the mess, I did it on my tablet and I did not use a stylus.
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    A schematic without values is as useless as a screen door in a submarine.
    I'm just curious about why you would want to limit your efficiency to 50%
    What you really should focus on is the efficiency. You need to look at the power input in watts and the power output also in watts. You should aim for an efficiency of 80% or better. The primary method for doing this is to focus on the quality of the magnetics and the characteristics of the switch. This is a highly non-linear circuit. The rules are all different
     
    Last edited: Nov 30, 2014
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    the caps and coil on the input are there for noise filtering. the choke and cap on the output are for for smoothing and filtering the dc. not for impedance matching.
     
  6. philm01

    Thread Starter Member

    Mar 22, 2014
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    Yes, that is what I am looking for. I am looking for techniques on how to design the transformer and the circuit so thhat I can have maximum power transfer to Rl.

    I can add values to my components but since I am looking for techniques/literature or something for maximum power transfer, I didn't think it was necessary.

    Now here is a curious queston. What happens if I switch the transfer at the LC resonant frequency on the secondary? My other objective is to obtain high voltage (>= 1kV) with 12 V in. Currently, I can input 5 V and get 4 kV across the secondary terminals but across Rl, I get only 30 V.
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    If you step up the voltage by a factor of 2 you cut the current in half. Power out will always be less than power in. You're wasting your time trying to get something for nothing. There's no free lunch.
     
  8. philm01

    Thread Starter Member

    Mar 22, 2014
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    0
    I understand that but right now, the ratio between my output power and input power is 0.008 at best. Is there anything that I can do to increase this ratio?
     
  9. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
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    How did you measure that ratio? Add some values to that schematic and describe in detail the transformer you are using.
     
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