1 Introduction

The audio amplifier market is increasingly adopting Class-D technology due to the rising power levels required by audio systems, limited space available for thermal dissipation, and tighter power consumption requirements. As the number of speakers grows and maximum power rail voltages increase, the power dissipation in the amplifier also increases resulting in even higher thermal levels, posing a significant challenge. To address this issue, power rail envelop tracking has emerged as a popular technique to enhance system-level efficiency. This allows audio systems to deliver the same powerful sound while prolonging battery life and minimizing heat generation.

Typically, audio systems operate with one voltage rail that can satisfy the system's maximum peak power specification. Since music is dynamic, this high voltage rail is only required for infrequent short bursts. Operating at this high voltage rail outside of those peak power levels results in significant losses without any benefit. More specifically, this inefficiency is due to switching and conduction losses. From a system level, operating at the max voltage rail only will result in poor battery life and higher operating temperatures. By implementing an envelope-tracking power-supply system, these system challenges can be effectively addressed. This approach involves analyzing the input audio signal to determine the optimal supply voltage level, and then dynamically adjusting the DC-DC converter's output voltage to match the audio signal's needs in real-time. Unlike traditional systems that maintain a constant voltage based on the peak power requirement, this approach ensures that the power supply voltage is always tailored to the specific demands of the audio signal without impacting THD. As a result, switching and conduction losses are significantly reduced, leading to substantial improvements in efficiency and thermal performance.

Figure 1-1 Figure 1: Class-H Disabled.

Figure 1-2 Figure 2: Class-H Enabled