LPF - high power output

Discussion in 'General Electronics Chat' started by Skeebopstop, Feb 15, 2009.

  1. Skeebopstop

    Thread Starter Active Member

    Jan 9, 2009
    Hey Guys,

    I am familiar with LPF for high output power concepts but am unsure of what type of inductor to choose.

    My application will need about 8A RMS and I have pasted a circuit I am referencing as this is my first audio venture.

    While looking at the circuit, why is there a requirement to add those bypass caps and snubber caps on the output stage? I figured them unecessary considering the waveform is already being smoothed by the big inductive low pass?

    Furthermore, why bother using a big inductive filter on the output stage when a speaker itself is basically just a massive inductor and resistor in series?

    Any insight would be greatly appreciated.

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  2. bertus


    Apr 5, 2008

    You are looking st the class D amplifier.
    This consists of a modulated PWM signal.
    The inductor is there to "smoothen" the PWM pulses to the audio signal.

  3. Skeebopstop

    Thread Starter Active Member

    Jan 9, 2009
    Hi Bertus,

    yes I realize that, but if the speaker itself is a big inductor, one I assume even larger than 18uH shown here, that will have a smoothing effect anyways.

    The only thing I can rationalize is to smooth the switching out as soon as possible for EMI etc.

    Furthermore, if I go and throw that inductive low pass filter on the output stage prior to knowing the inductance of the speaker, how can I say I'm not filtering out more than I want to?

    I.e. the LPF shown above has a bandwidth of about 30kHz as it is designed for 4 Ohm speakers. This is before considering the inductance of the speaker, so in reality, the bandwidth should be less?
  4. kubeek


    Sep 20, 2005
    I am not a pro in D amps, but I guess it is to prevent destroying of HF speakers, and maybe for stability reasons too.
    But anyway, ask at http://diyaudio.com there sure are people who can explain it to the slightest details.