Buck converter

Discussion in 'The Projects Forum' started by jayzac, Jan 12, 2011.

  1. jayzac

    Thread Starter New Member

    Apr 24, 2009
    6
    0
    Hi,
    I am designing a buck converter to step down the voltage down to 12V. What is the difference in choosing the power transistor between pmos and nmos for this design ?

    Thank you.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Step down WHAT voltage?

    If it's mains powered, the output must be isolated from mains power by coupled inductors (ie: transformer).

    For buck-type designs, N-ch MOSFETs require a high-side driver. P-ch MOSFETs don't; but their gate charge is ~2.5 times higher than that of an equivalent N-ch MOSFET. This means the gate drive needs to be considerably "beefier" than that of an N-ch, otherwise high power dissipation in the MOSFET will result.

    http://www.smps.us has lots of good information on switching supplies.
     
  3. jayzac

    Thread Starter New Member

    Apr 24, 2009
    6
    0
    The design is to step down 20W solar panel of Vpp about 18V to 12V. So the pmos is applicable in this design by just using a normal npn transistor to drive the pmos ?
     
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