Class G:
Class
“G” Topology uses two +/- rail power supplies connected via
a power diode and a MOSFET working as a power switch.
At
low levels +/- VCC1 supplies current to output transistors, and
VCC2 supplies are disabled (MOSFETs are open).
When
driver reaches +/- VCC threshold, comparator +SW & -SW
turn
on MOSFETs, switching from low voltage power supply rails to the
higher voltage rails.
In
this way power dissipation and efficiency are optimized for the
specified power level.
Advantages:
Basic amplifier
topology is Class A/B, so linearity and EMI issues are
minimized.
A fairly efficient
amplifier which can deliver the specified output power with a
smaller transformer and less heat-sinking than a conventional
Class AB amp.
Disadvantages:
Circuit complexity
increases adding cost.
Cross over distortion
similar to Class B, switching distortion occurs at each output
level transition (when the power supplies switches from rail to
rail, noise can be generated).
Conclusion:
Topology used in high efficient amplifiers, where cost and
distortion are not major factors.
