simpliest isolated dc/dc converter???

Discussion in 'The Projects Forum' started by settra, Nov 10, 2013.

  1. settra

    Thread Starter New Member

    Apr 16, 2010
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    hello forum. i want to make a simple isolated dc/dc converter, that has Vin from 10 to 16v (Car battery ) and fixed 12v outpout. (and 3A ).
    can anyone share with me a simple schematic, with some basic explanation ??

    because in all the schematics i find, i have a hard time, understanding how the feedback is done...
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    A buck converter is not isolated. For that you need a circuit with a transformer, such as a flyback design. Why do you need isolation?
     
  3. settra

    Thread Starter New Member

    Apr 16, 2010
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    i have an LCD in my car, tha i power from a non-isolated switchg converter, but i have a ground loop somewhere, but in 2 years now i cant find it to break it...

    so the only way to break it, would be to make the LCD power supply, isolated from the rest of the system !!
     
  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    Use a 2 transistor push-pull forward converter. Flyback could also work, but with low VIN like 12V, we always used a push-pull to get best utilization of the available input voltage.
     
  5. settra

    Thread Starter New Member

    Apr 16, 2010
    8
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    hm? can you expain a bit more please?? remember, i need an isolated dc-dc converter...

    something like this : [​IMG]

    only , much more simple, and without a chip, becouse it limits the outpout...
     
  6. settra

    Thread Starter New Member

    Apr 16, 2010
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    0
    bountyhunter. after a bit of search, i see that flyback and push pull that you mentioned, are exactly what i was looking for!!

    but why not flyback?? since i dont require much power (30watt) OR efficiency (After all, this is my first attempt in power supplies, so it dosent have to be the best) , i could even use a linear voltage regulator (like 9v or something ) to make calculations easier!! the only thing that is a must, is the isolation ;)

    in a flyback design, how would i modify the pulse width and frequency, with an optocoupler??

    and the two coils i will be using, what exactly do i look for?? (2 coils side by side, or a coil, with enother coil around it in 1-1 ratio?? )
     
  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    Flyback would probably be OK, just lower efficiency. I recommend you go to the TI website and use the simple switcher software on the LM-2577 or similar devices. They will design the whole flyback converter for you and give the part numbers. They have transformers in their parts data base.
     
  8. settra

    Thread Starter New Member

    Apr 16, 2010
    8
    0
    i also found LT4748 to be nice... can you tell me exactly what is the software you speak of? because, i downloaded something, but it dosent implement any IC's...
     
  9. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,978
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    Cant find the LT4748 listed, but several others isolated regulators..
     
  10. settra

    Thread Starter New Member

    Apr 16, 2010
    8
    0
    crap. i mean LT3748.

    well just now, i found out, that even finding IC's like this, where i leave, would be a bit hard...

    is there any current driven PWM source, i could use, as a controller?? ( a pretty common one)
     
  11. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Where do you live,?
     
  12. settra

    Thread Starter New Member

    Apr 16, 2010
    8
    0
    i leave at greece!!
     
  13. settra

    Thread Starter New Member

    Apr 16, 2010
    8
    0
    actually, i now have another problem.

    if the isolated dc/dc converter, powers an LCD.

    and the LCD gets the signal from a PC, that is grounded somewhere else.

    inside the LCD, the signal cable grounds, are connected to the power cables ground....
    so , wouldent that , short the 2 different grounds, into one??
     
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