P channel amplifier

Discussion in 'The Projects Forum' started by Experimentonomen, Apr 6, 2012.

  1. Experimentonomen

    Thread Starter Member

    Feb 16, 2011
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    This "project" was originally started sometime in 2010-2011 after a friend asked me if p channel devices could make an amp, i thought "why not?" and developed a circuit using only p channel mosfets in the output stage.

    However the friend was unable to make the circuit work, so then i tried it, and after some fiddling around i managed to get it working, this was the results: P Channel mosfet amp - YouTube

    Shortly after that video was taken, i more or less put this project aside and eventually forgot about it, until yesterday when i got a pm about it.

    So today i decided to revisit this old project, said and done, i repopulated the board from the old project with the components that had since been taken and hooked up two IRF9540's.

    A few pics: http://i.imgur.com/sQa9U.jpg http://i.imgur.com/JlTVM.jpg http://i.imgur.com/KqTRW.jpg

    Power on, adjust bias and done. This is the circuit if anyones interested in trying it: http://i.imgur.com/A5zLE.png

    In my opinion it actually sounds pretty good for what it is, so i might go all the way and build a stereo version, i'll update this thread if that happens.
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    Usually the output of a power amplifier is able to symmetrically swing close to the positive and negative supply voltages.
    But the output of your "P-channel" amplifier cannot swing close to the negative supply voltage but swings close to the positive supply voltage.

    The maximum gate to source voltage in your circuit exceeds the maximum allowed gate-source voltage so the Mosfets will blow up.
     
  3. Experimentonomen

    Thread Starter Member

    Feb 16, 2011
    331
    46
    I havent had any problems so far and i have had this thing up to severe clipping.
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    896
    But the bottom driver transistor is an emitter-follower with about 1V of loss and the Mosfet is also a follower with about 6V or more of loss.

    The top driver transistor and Mosfet have very low voltage losses.

    Then the clipping is severely asymmetrical.
     
  5. Experimentonomen

    Thread Starter Member

    Feb 16, 2011
    331
    46
    N channel amplifiers have the exact same problem as its literally the same thing turned upside down.

    Assymetrical clipping is usually not an issue, even most complementary designs have assymetrical clipping unless the input and drive is also complementary and symmetrical.
     
  6. Experimentonomen

    Thread Starter Member

    Feb 16, 2011
    331
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    I built a second channel: http://i.imgur.com/hDTgX.jpg

    Main reason i built this is because i have much more IRF9540 p channel devices than i have IRF540 n channel devices, and p channel devices on their own are pretty useless for anything other than this.
     
  7. Experimentonomen

    Thread Starter Member

    Feb 16, 2011
    331
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