Is it possible to use a buck converter as booster (with a transformer)?

Discussion in 'General Electronics Chat' started by takao21203, Mar 26, 2013.

  1. takao21203

    Thread Starter Distinguished Member

    Apr 28, 2012
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    This is one idea I have but I am not really sure about it.

    Since I have very small ferrite transformers here I want to try it eventually.

    The primary has a few turns. The secondary has much thinner wire.

    Is it possible to build it as buck converter, with a PNP transistor, but then generate a higher voltage from the secondary winding?

    What is the schematic for that? OK simple, I know buck converter, but isn't it correct it is used in continuous mode and no capacitor is charged from the primary inductance?

    Would this be a proper circuit?

    Or should I simply use a booster circuit + NPN?

    I am just curious to do more experiments, using small transformers now or coils, even ringcores. To learn more about it, I do not need to build anything for a specific purpose.

    Also a picture from the transformer. It is not a photo Flash transformer, but the secondary has much more windings than the primary.

    Also want to try it with a LNK IC eventually. It is not a transformerless supply! Maybe the transformer will just explode, but maybe will work just fine.
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Buck would not bee very useful, as the inductor feeds the output capacitor directly. Boost however is basically the same topology as a flyback. See smps.us/topologies.html for comparison.
     
  3. takao21203

    Thread Starter Distinguished Member

    Apr 28, 2012
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    Yes I know but what if I don't use a capacitor, short the inductor to ground, and remove energy via the secondary winding?

    I was thinking as long as the pulses are short enough so the primary does not saturate, I could get away with that.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    That's basically a flyback converter, as kubeek stated.
     
  5. takao21203

    Thread Starter Distinguished Member

    Apr 28, 2012
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    Yes I understand that somehow, even if I am of course still learning about these circuits.

    My question is if I could use a PNP for a flyback? Or does it even make any difference?
     
  6. crutschow

    Expert

    Mar 14, 2008
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    It's not typically done but you could if you used it as a high side switch driving the grounded primary. Normally the low side is switched since NPN's or N-MOSFETS have higher gain, are somewhat faster, and it's easier to drive a low-side switch.
     
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