A class B switch-mode assisted linear amplifier

doi:10.1109/TPEL.2003.818825

2003-11-01

PRE

Geoffrey R. Walker *

DOI：10.1109/TPEL.2003.818825

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摘要

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A switch-mode assisted linear amplifier (SMALA) combining a linear (Class B) and a switch-mode (Class D) amplifier is presented. The usual single hysteretic controlled half-bridge current dumping stage is replaced by two parallel buck converter stages, in a parallel voltage controlled topology. These operate independently: one buck converter sources current to assist the upper Class B output device, and a complementary converter sinks current to assist the lower device. This topology lends itself to a novel control approach of a dead-band at low power levels where neither class D amplifier assists, allowing the class B amplifier to supply the load without interference, ensuring high fidelity. A 20 W implementation demonstrates 85% efficiency, with distortion below 0.08% measured across the full audio bandwidth at 15 W. The class D amplifier begins assisting at 2 W, and below this value, the distortion was below 0.03%. Complete circuitry is given, showing the simplicity of the additional class D amplifier and its corresponding control circuitry.

Keyword:

class B amplifier

class D amplifier

dead-band

distortion

half-bridge current

hysteretic controlled

parallel buck converter

SMALA

topology