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Justification for the need for high voltage/power Class D amplifiers

Discussion in 'Electronic Basics' started by Matthew, Nov 16, 2004.

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  1. Matthew

    Matthew Guest

    Hi,

    I am doing a study in Class D power driver. Currently, reviewing the
    market feasibility. However, I have some questions.

    1) What is the purpose of designing high voltage Class D power driver
    if it is not for portable devices? Isn't a Class AB enough to meet
    such requirements?

    2) In what ways and why will Class D replace Class AB in the future?

    I understand that Class D has the following advantages:

    a)Compactness of overall design;
    b)Lower heat dissipation/high efficiency;
    c)Cost saving
    d)Energy saving

    Are there any other compelling reasons that Class D will replace Class
    AB?

    Appreciate any help.

    Thanks.
     
  2. One application is high power pro audio gear. Once you get into the 1kW+
    range it starts making better sense.
    It won't.
    There is little correlation between physical size and method. In fact,
    Class D usually requires more complicated circuitry to obtain decent
    performance.
    There aren't any compelling reasons for class D. Its just another method
    that had advantages in some situations, and disadvantages in others.
    Class D wont replace the other methods it is used in addition to the
    other methods.

    If your doing a study your supposed to identify the disadvantages as
    well as the advantages. You seem to be assuming the Class D is god's
    gift to amplifiers from the outset. It isn't.

    Kevin Aylward

    http://www.anasoft.co.uk
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
     
  3. john jardine

    john jardine Guest

    Off hand it smacks of homework.
    They're probably also indoctrinating 'em that digital will always replace
    analogue and that nothing worthy is designed below 10GHz and that microsoft
    is the best thing since sliced bread.
    regards
    john
     
  4. rayjking

    rayjking Guest

    Matthew,

    The efficiency is better but a close second is crossover distortion. True
    Class D has no cross over distortion also the design is more simple over
    the temperature range because one fet is switched full on or off.

    Ray
     
  5. rayjking

    rayjking Guest

    Matthew,
    Correction to my post. The other advantage to a switcher vs AB is the
    voltage rating of the switch and size of the out put transformer along with
    the power loss due to the bias current in the output transformer.
    a very good pwm can be made with two 555s and one IR2111. driving two
    totempole N fets.

    Ray
     
  6. Bob Masta

    Bob Masta Guest


    Good article in EDN, Nov 11, 2004 called "Getting
    the most from Class D multichannel audio amplifiers".
    Mentions one aspect that I had not considered about
    class D... they have *no* power supply rejection at all!
    Whatever trash comes through the supply, comes out
    the output because all these amps do is switch the
    supply off and on.

    I guess there are still a few legs (ie feedback) left to linear
    circuits after all. <g>

    Best regards,


    Bob Masta
    dqatechATdaqartaDOTcom

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
     
  7. Clarence

    Clarence Guest


    This was made clear to me when I built a Class 'D' amp for a signal with a
    constant amplitude of 121.6 Volts P/P and which had to degrade linearly down to
    56.6 Volts P/P as the current went from 100% (nominal) to 300% of (nominal) and
    shut off if the load increased further. As load current increased there was a
    corresponding increase in ripple on the signal. The circuit was complicated by
    the need to put 'ripple stripers' on both polarity outputs. MESSY!
     
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