Switching audio amplifiers save battery life

摘要

As portable-electronics consumers demand smaller devices with longer battery life, designers are looking to replace conventional linear amplifiers with high-efficiency devices. Although Class AB amplifiers have long dominated the world of audio, Class D (switch-mode) amplifiers provide the balance between efficiency and distortion re-quired by portable devices. A switch-mode amplifier consists of an H-bridge and a load (see Fig. 1). The load includes the speaker impedance and a passive filter. The H-bridge steers current to the speaker, and the LC filter attenuates the switching noise. To understand more clearly why this method is better suited to portable devices than the conventional linear amplifier is, we must examine the advantages and pitfalls of each topology.