|
| Class "AB" |
| Class AB topology uses two output
devices, in a class AB configuration, and applied bias to the base
emitters junctions, so that both of the output devices are slightly
conducting (Ic = 3 mA), in order to minimize cross-over distortion.
The result is a close to class B efficiency and near class A in low
distortion. This is attributed to a class A current source with bias
voltage applied to class B outputs. Efficiency is 45-50% and class
AB amplifier requires moderate heat sinking. |
| Advantages |
| Low quiescent current compared to
class A, and low distortion |
| Disadvantages |
| Higher quiescent current than class B,
Current source must be precise controlled in order to prevent
thermal runaway, Voltage source V must precise controlled. When bias
transistor is used it must be attached to heat sink to track the
temperature of the output devices. |
| Conclusions and
comments |
| Class AB is the most accepted topology
in the electronics industry due simplicity of design, relatively low
distortion, minimum sink current required, and low cost. |
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