What is a Class D amplifier?

A Class D amplifier is a specialized amplifier that operates its active devices (like transistors or MOSFETs) purely as electronic switches. They rapidly toggle between fully "on" and fully "off" states rather than operating in a linear, proportional region. Because the devices are rarely in a state of partial conduction where they would dissipate significant heat, Class D amplifiers can achieve extremely high efficiency levels, often exceeding 90 percent. They do not inherently use "drift-mode" FETs, nor are they naturally free from distortion prior to output filtering.