Class G/H:
Class G/H topology
uses a minimum of two +/- rail Power Supplies connected via
power diodes.
At low output power
levels only +/- VCC1 supplies current to the outputs and VCC2
& VCC3 are disabled.
At medium power Q2 is
enabled and VCC2 is switched on (and VCC1 is opened).
When signal reaches
VCC2, Q3 starts to supply current, and Q1&2 are in
saturation. In
this way power dissipation and efficiency are optimized over the
power range of voltage on the amplifier.
Advantages
Efficient amplifier
which can deliver the same output power with a smaller power
supply transformer and a smaller heat-sink.
Disadvantages
Circuit complexity
adds cost (expensive multi-tap transformer and multiple output
devices).
Crossover distortion
similar to Class B switching distortion occurs at each output
level transition, when supplies switch from rail to rail.
Potentially high THD @ high audio frequencies.
Crossover distortion
is not at zero crossing point but also at 1/3 and 3/4 of maximum
output signal
Conclusion
Class G/H topology is
used in high efficient amplifiers where the cost and distortion
are not an object.
