Pulse Width Modulation - Class D amplifier

Class D amplifiers

First: Input signal.
Second: Carrier triangle signal.
Third: PWM signal.
Fourth: Filtered speaker output (low pass RLC).

Highly efficient are the class D amplifiers. Up to 90-95% of power given to it goes to your speaker.

Ideally, they are the best kind of amplifiers with distortion only in the very high and inaudible frequencies (which usually gets passively filtered out anyway). In practice, they also suffer from distortion due to switch times between the high and low states of the output.

How does it work?

The input signal is modulated over a carrier frequency and morphed into a pulse width modulation signal. An irregular square wave with flat top and bottom, all or nothing.

Food for thought: Mathematically speaking, a square wave can be thought of as a compound of multiple sinusoidal frequencies.

The PWM signal is then fed to the output stage, which could be just 2 MOSFETs, then passively filtered to remove all the undesirable higher frequencies. We keep in mind that audible frequencies are below 20kHz, unless you are Batman, because bats hear ultrasounds. A class D amp might not be Batman's first choice.

DIY PWM amp by "Great Scott"

© ChillPill 2020

Class D amplifier - Pulse Width Modulation