Current Drive Can Overcome Pitfalls Of Class D Audio Amplifiers
by Anthony Esposito, Avatar Engineering, Fountain Hills, Ariz., How2Power Today, Mar 13 2020
Focus:
MRI gradient amplifiers perform similarly to class D audio amplifiers except that
their high power and absolute accuracy is well beyond what commercial audio amplifiers
can achieve. In the MRI, the drive employs a controlled current to create an accurate
magnetic field gradient across the patient without direct feedback of the magnetic
field. The driven gradient coils are complex loads and are typically modeled as third-
or fifth-order impedances. Driving these complex impedances with a controlled current
rather than voltage, results in greater accuracy. As this article explains, the same
benefit can be obtained when driving a loudspeaker with a current and this approach
also eliminates errors associated with using class D amplifiers to drive speakers, as
well as the need to adopt GaN power transistors. This article explains operation of
class D amplifiers conceptually, identifies their sources of error, compares current
sensing vs voltage sensing feedback, presents simple electrical models of
loudspeakers, and describes a circuit alternative to class D, a current-controlled
amplifier employing hysteretic control.
What you’ll learn:
- How to drive audio amplifiers more accurately using current rather than voltage drive
- How to understand the operation of class D amplifiers
- How to understand the sources of error in class D amplifiers
View this Source (requires a PDF Viewer installed on your device)
© 2025 How2Power. All rights reserved.