positive output Luo converter

Discussion in 'The Projects Forum' started by lang, Jul 19, 2011.

  1. lang

    Thread Starter New Member

    Jul 19, 2011
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    howsit ppl,

    I'm new on the site and was wondering if somebody could help me. I am doing a project on the Luo converter. I have to design a 16 stage Luo converter to step up 12V dc to 2400V dc (or maximum output voltage attainable) with open loop control and continuous supply of 1mA current. project must work in continuos and discontinuos modes.

    I'm trying to design it stage by stage, 1,2,4,8,16. when I design the inductors I get very high values and low values for caps.

    I managed to scale them for the first 4 stages but when I get to eight stages my voltage just doesn't go above 750Vdc no matter what I do.

    any assistance will be much appreciated.
     
  2. lang

    Thread Starter New Member

    Jul 19, 2011
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    0
    by the way, these were the equations I used:
    for continuous mode:

    Lmin>=kr/fL

    where L is the value of the inductor of the filter at th end of the circuit.

    Cmin>=6.25((1-k)k)/f^2*Lmin

    where k is the duty cycle of the pwm and f is the frequency.
     
  3. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    488
    Sorry , never worked with one of those.

    Question: If you decrease your load current, does the voltage go up?

    What are the values you got for L and C?
    What frequency and duty cycle did you use? Does the voltage change when you change frequency/duty cycle?

    See also attached pdf.
     
  4. lang

    Thread Starter New Member

    Jul 19, 2011
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    I got quite big L values and small C values but when I scaled them I ended up with 6mH, 3mH and 1000uF.

    duty cycle is proportional to voltage output. load does not affect the voltage output in continuous mode.

    thanks for the pdf, hope it helps.

    do you perhaps know if the voltage saturates in a typical boost converter?

    it is like a boost converter with a few other components. I am sure any difficulties with the boost should provide some knowledge about this converter.

    thanks again.
     
  5. lang

    Thread Starter New Member

    Jul 19, 2011
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    hey,

    I also forgot to mention that I have a set switching frequency of 1kHz.

    the pdf you sent to me is a super lift luo converter. the voltage increases in geometric progression. can't use 16 stage super lift. I need to use standard luo converter where gain=1/1-k and the voltage increases in arithmetic progression.
     
  6. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    If I used a boost converter without regulation I'd think that the maximum output voltage was predominantly determined by the amount of energy you store in the inductor, the characteristics of the inductor, input voltage, duty cycle, and the load...

    Maybe some of the other folks here have an answer to your Luo-converter question. :(

    Can you post a schematic of your circuit?
     
  7. lang

    Thread Starter New Member

    Jul 19, 2011
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    here's a schematic of 4 stage and 3 stage. I need to do a 16 stage. I think I might have found the problem. the energy transfer over so many stages is not possible with diodes acting as switches rather than mosfets.
     
  8. lang

    Thread Starter New Member

    Jul 19, 2011
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    can you also tell me a bit more about open loop control?

    I know that there is no feedback but all the diagrams I come across are about using comparators or flip flops or some kind of op-amp.

    is there not an easier way to control the duty cycle, voltage output etc?
     
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