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multiple output flyback converter

Discussion in 'Electronic Design' started by tech_savvy, Jan 3, 2005.

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  1. tech_savvy

    tech_savvy Guest

    I wanted to design flyback converter.
    How to determine transformer specifications...IC to be used...etc.
    Vpri=5 V,Vsec=5V(8 secondaries),Isec=200mA each.
     
  2. John Larkin

    John Larkin Guest


    You might as well ask how to build your own helicopter.

    John
     
  3. Leon Heller

    Leon Heller Guest


    http://schmidt-walter.fbe.fh-darmstadt.de/

    Leon
     
  4. Ken Smith

    Ken Smith Guest


    5V * 200mA * 8 = 8W this is quite posible with many chips

    The input side current will be a few amps, lets say 5. Look for a chip
    that can handle that much.

    Pretend that you have just one secondary with 1.6A of load and follow any
    of the many app-notes for doing that design.

    You need a low leakage inductance in the transformer. This should work
    for you:

    Your inductor will be a 1:1 so take 16 wires, form a wire rope, wind the
    inductor and then use 8 in parallel as the primary. Try to spread the
    primary windings evenly around in the wire rope and the 8 others as the
    secondary.
     
  5. Rich Grise

    Rich Grise Guest

    I think that if they guy thinks flyback is appropriate for 1:1, he needs
    to re-take the course.

    Or maybe he thinks he needs a flyback because in the diagram, the
    stack of secondaries is so tall. ;-p

    Cheers!
    Rich
     
  6. Ken Smith

    Ken Smith Guest

    Flyback designs work just fine at a 1:1 ratio. With a 1:1 transformer,
    the switching waveform has equal transistor and diode conduction times.

    It is about the only way that one inductive element can give you many
    semi-regulated outputs. Current-fed, psudo-resonant and true resonant
    designs generally need two inductors. Voltage fed forward converters need
    N inductors for N outputs.
     
  7. Hey Ken,
    Since it is a 1:1 Flyback, might as well add the cap from drain to output
    diode anode and gets the benefits of a SEPIC. Leakage inductance causes no
    ringing, cleaner switching. Eight outputs, eight coupling caps, unless he
    wants isolation which was not stated.
    cheers, harry
     
  8. Ken Smith

    Ken Smith Guest

    I take 8 outputs to imply 8 isolated outputs. If they are not isolated,
    there is little reason to make 8 instead of one. For that matter, his
    input and output voltages were equal so he could use 8 wires if isolation
    was not needed. The 8 wires solution produces a lot less ringing than
    even the SEPIC design would.
     
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