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constant output why for buck converter????

Discussion in 'General Electronics Discussion' started by noman, Oct 17, 2012.

  1. noman

    noman

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    Oct 17, 2012
    ![simplest buck convrter][1]



    The is serious problem with this design. When i apply a gate signal, the output voltage is around 10 or 11V no matter how much i change the duty cycle. It remains near 10V when duty cycle is 10% and almost the same when i increase the duty cycle to 70%. Can some body explain the reason.
     

    Attached Files:

  2. BobK

    BobK

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    Jan 5, 2010
    Well, for starters you are using an N-channel MOSFET where a P-channel is needed.

    bob
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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  4. BobK

    BobK

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    Jan 5, 2010
    If the input and the load are constant, you can run a buck converter without feedback. Be aware though, that the formula:

    Vout = Vin * D

    Works only when the converter is running in continuous mode, i.e. the current in the inductor never saturates or falls to zero, it must look like a sawtooth. With a fixed load, choosing the inductor value and the frequency can make this happen. With small variations in the load, it might still work out, but with an order of mangnitude variation, you are not going to be able to make it continuous at both ends.

    Bob
     
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