increasingly popular in recent years. What are Class D amplifiers?
How do they compare with other kinds of amplifiers? Why is
Class D of interest for audio? What is needed to make a “good”
audio Class D amplifier? What are the features of ADI’s Class D
amplifier products?
The Class D Amplifier Advantage
In a conventional transistor amplifier, the output stage contains
transistors that supply the instantaneous continuous output
current. The many possible implementations for audio systems
include Classes A, AB, and B. Compared with Class D designs,
the output-stage power dissipation is large in even the most
efficient linear output stages. This difference gives Class D
significant advantages in many applications because the lower
power dissipation produces less heat, saves circuit board space
and cost, and extends battery life in portable systems.
Thanks to a different topology the Class D amplifier
dissipates much less power than any of the above. Its output stage
switches between the positive and negative power supplies so as
to produce a train of voltage pulses. This waveform is benign for
power dissipation, because the output transistors have zero current
when not switching, and have low V
DS when they are conducting
current, thus giving smaller I
DS 3 V
DS
