High-Efficiency Class D Audio Amplifiers Extend Battery Life in Portable Applications

Abstract: This application note examines the operation and benefits of a Class D (switch-mode and filterless) audio amplifier. Switch-mode amplifiers such as the mono MAX4295 and stereo filterless MAX9701 offer high quality audio with improved efficiency when compared to traditional linear audio amplifiers (Class A, Class B, and Class AB). This application note presents an overview of traditional linear audio amplifier designs and then compares them with Class D amplifier design. The benefits of newer Class G amplifiers are acknowledged. The article shows efficiency calculations and output filter design for Class D amplifiers. The high efficiency of Class D amplifiers is demonstrated with the MAX9701.