class D amplifier powered from PC power supply questions

Discussion in 'Power Electronics' started by T3STY, Oct 9, 2016.

  1. T3STY

    Thread Starter New Member

    Oct 4, 2016
    16
    0
    Hello everyone,

    I was thinking of integrating a small 2x20W @8Ohm class D amplifier in my PC, which I think it's small and loud enough for my needs.
    However, most of the amplifier boards that I could find need a 15V minimum power supply, recommended for most is 19V and some other are 24V; current requirements (in full load, at maximum volume) is somewhere around 3A to 4A.

    At first I thought I could just buy a 19V 4A power suply, and simply power it from the 220V mains, but then, I realized that the amount of space in the build that I'm making is way more limited to fit such power supply.
    So, why not using a DC-DC boost converter? It's fairly small; it can be powered from PC's 12V output, and the output power is within the recommended amplifier requirements.

    But I am no electronics specialist, and a few things read on the internet in some occasions, prevent me from taking this solution for granted.
    I usually read about not powering amplifier boards with PC's power supply because the audio amplification is a non-constant load, which causes fast varying current draws from the PC power supply, and it may not be healthy for it. Wouldn't this be applicable to usual class A/B amplifiers?
    I also read that DC-DC converters can introduce (other than high frequency audible noise) voltage noise in the PC power supply. Isn't this limited (to a certain degree) to the DC-DC converter quality? Can I build small filter that would prevent this from happening, or just reduce it enough to be careless about it?

    Can you confirm the above?
    Are there other issues that I should worry about?

    I have also found an amplifier board that uses the MAX98400A and can be powered directly from a 12V power source (8V-28V power supply range). Would this be a better solution?
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,801
    1,105
    Yes, if the audio output power is acceptable.
     
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  3. T3STY

    Thread Starter New Member

    Oct 4, 2016
    16
    0
    Hello Alec,
    By looking at the output power vs supply voltage graphic into 8Ohm load, it seems the output power at 12V is a little over 15W. It is enough for my needs (games and movies while standing in front of the PC). I could just build 4Ohm speakers to achieve more output power (I could read 20W output power from the graphic), but that's not actually a must.

    Anyway, I'm still looking forward into answers to my other questions. If someone could answer them it would be great!
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,023
    3,236
    I don't think running a DC-DC converter from the computer 12V will be a particular problem.
    Any significant noise should be filtered by the supply capacitors.
    I do have a concern about overloading the 12V supply, but that probably won't occur at normal listening levels.
    I don't see the varying load of the amp as a problem for the 12V supply as it should be able to readily adjust to the change without difficulty. I certainly don't see anything "unhealthy" about that.
     
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  5. T3STY

    Thread Starter New Member

    Oct 4, 2016
    16
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    Hi crutschow,
    I have performed an accurate research on the power needed for this build, and I'll make sure the 12V line has enough power for all of those. Or maybe, is the overloading issue something independent of the power supply capabilities?
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,023
    3,236
    No.
    As long as the 12V power is sufficient for both the computer needs and the power amplifier draw.
     
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  7. T3STY

    Thread Starter New Member

    Oct 4, 2016
    16
    0
    Thank you very much for your answers, guys :)
     
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