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[needing guidance] high power flyback transformer

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by laharl2k, Jan 24, 2012.

  1. laharl2k

    laharl2k Member

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    well still with my "ultimate" fan controler, i saw that using pwm to control capasitive loads is a big no, so desided to use a buck converter, but as p channel mosfets arround here aren't big enough, i decided to use a n channel one and instead use a flyback converter, and btw add overvolting capability.

    the thing is i need something to take 12V and output from 0 up to 40V, with reatively high eficcience.
    say about 16A @ 12V.....about 200W, i need to make 3 of these, so they have to be rather small, and the power limit is in general between the three.
    The voltage contro in done by a micro that i already programed and all, so the only thing left for me is this.
    But i couldn't find much about good practices and formulas to make a smps of more than 1-2A.

    i made a few tests with the transformer from an atx psu, originaly it worked at 50khz but in some tests i had no problems switching at 500khz and the efficiency went a little bit higher. but even with little load efficiency was horrible....and the mosfet got warm with less than 500mA, (i did everything i knew right yet the secundary doesn't seem to discharge properly, so the mosfet's diode takes the rest...).
    also made my own toroid.....u.u

    i'm missing a lot of knowledge here so info, what should i look at, where, or a better alternative, whatever that could help me would be really apreciated as this is the only thing holding this proyect.

    also the pwm control i made works like s*** (triangle > opamp > 555, with another opamp controling the one that generates the output), and the coil starts making noise even though the voltage stays stable.

    don't know where else to look, thanks in advance u_u
     
    Last edited: Jan 24, 2012
  2. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    I would look at IT.com, Onsemi or any where where PWM ICs are sold. There are good application notes. Coilcraft.com has some application notes on transformers. I know you are not using a PWN IC but the information is the same.

    You do know that to get 40V at 2A you will need 12V at 8A. Do you need to go to 0V out? If 12V is the minimum that allows you to use 'boost'.
     
  3. laharl2k

    laharl2k Member

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    about the 0V, no one is gonna use 0V but the idea is to lower the voltage to lower the fan's speed. from 12.00000001V and up is overvolting, that's the plus. i thought of doing a boost and then three buck, but i think it's simpler and cheaper to make 3 flyback. i mean sync boost and three sync boost cant be easier than 3 sync flyback alone, add the fact that i can't find a 16A+ p channel mosfet.

    and what do u mean with 2A@40V with 8A@12V? 12V*8A=96W->/40V=2,4A, so 16Ax12V=192W->/40V=4,8A, don't get why u ask, if it's bcause of the current then don't worry, a good atx psu can give a lot of amperage, i've seen some with more than 70A, enough to start an engine. and the conectors, ill use the ones that are used in high end video cards, that eat about 200W
     
  4. dave

    Dave New Member

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  5. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    Watts in must be slightly greater than watts out. Several times recently someone wants to build a 12V @1A in, 40Vout @ 1A out and things don't work that way.

    A simple boost; vout >= vin.
    If Vout must be smaller than vin then use a flyback or SEPIC. http://www.coilcraft.com/apps/sepic/selector_2.cfm
     
  6. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    This application note might help.
     
  7. laharl2k

    laharl2k Member

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    oh yes, i know, but 16A and 4,8A are the output, that's why i said 16A+ pmos, i know you have to take into account the loses.
    and i was just looking into that sepic converter at coilcraft. looks like a good solution. i'll see it in more detail tomorrow, 0:50AM here, so i'm going to bed, thanks for the help.
     
  8. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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    9pm here, doing the same
     

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