Class D Amplifiers!!

Discussion in 'General Electronics Chat' started by tck1911, Nov 13, 2012.

  1. tck1911

    Thread Starter New Member

    Nov 12, 2012

    Could someone tell me the reason for using a Low Pass Filter in a Class D Power Amplifier?

    Also, what sort of a Low Pass Filter (Fisrt order, second order, active, passive) should be used when designing a Class D amp?

  2. Wendy


    Mar 24, 2008
    The filter type isn't that important, basically Class D uses a form of PWM, and needs the high frequency removed, which is the reason for the filter.

    Here is a article I wrote for the AAC book...

    Pulse Width Modulation

    My blog...

    Bill's Index

    A very long while back I helped a user design one using a M-Derived filter (low pass). They are a stone cold dog to tune though.
    tck1911 likes this.
  3. MrChips


    Oct 2, 2009
    The output from a Class D amplifier switches voltages on and off, i.e. it is a pulse-width modulated (PWM) signal. You don't want to feed this directly into the loudspeaker. This high frequency signal must be smoothed out using a Low Pass Filter (LPF).

    It makes no sense using an active filter because that would require a linear power amplifier, defeating the whole purpose of a Class D amplifier.

    A passive filter using an inductor and a capacitor would give you a second order filter.
    tck1911 likes this.