Calculating power delivered by supply

Discussion in 'General Electronics Chat' started by Distort10n, Feb 8, 2008.

  1. Distort10n

    Thread Starter Active Member

    Dec 25, 2006
    429
    1
    I have an interesting question based on ADI's SSM2211 audio amplifier:

    http://www.analog.com/UploadedFiles/Data_Sheets/SSM2211.pdf

    On pg. 16 they are deriving power efficieny as the difference between the power delivered by the supply and the power delivered to the load by the amp. Equations 3 and 5 are of interest.

    The text explains that equation 3 and 5 are expressed in terms of peak voltage. This makes sense for equation 3 which is really the RMS value of power expressed in terms of peak voltage. A simple algebra manipulation.

    I do not see this in equation 5. They are stating they are expressing the average current as a peak voltage, but the equation itself is literally the average value of a sinusiodal current waveform, rather than an RMS waveform expressed as a peak signal similar to equation 3.

    Are they not mixing apples and oranges here? RMS and Average values?

    It seems they are trying to obtain similar variables, Vpeak, to derive equation 6. and 7 I am not questioning the validity of the actual average value equation, just the purpose of using it to derive a power caluation.
     
  2. Distort10n

    Thread Starter Active Member

    Dec 25, 2006
    429
    1
    I found out that the SSM2211 datasheet is correct in terms of calculating power delivered by the supply. However, equation 7 is incorrect as stated in the datasheet. The correct derivation of internal power dissipation expressed in terms of power delivered to the load is attached.
     
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