Class D audio amplifier using PIC24FV16KM202 block diagram

Class D amplifiers have become a popular audio amplifier topology due to their high efficiency and subsequent low cost. The high current output stage is implemented using binary switches, resulting in minimal heat generation and power loss. This allows for the power supply, heat sink and overall physical size of the amplifier to be minimized. Typical efficiency of a class D amplifier is over 90%, as opposed to 50% for a typical class AB amplifier. In an AB design, most of the inefficiency is a result of the output stage devices being required to operate in the linear region. As current flows though the devices, it is converted to heat instead of being delivered to the load.

CLASS D TOPOLOGY OVERVIEW
A Class D audio amplifier is essentially a PWM amplifier. The input audio signal is used as the modulation reference for a PWM carrier. The resulting PWM signal is used to drive a higher power output stage, and filtered to recover the amplified audio. A class D amplifier is composed of 4 main functions as shown in Figure 1.

These functions are:
• Triangle wave generator
• Audio modulation comparator
• Switch controller and output stage
• Low pass filter

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