Class H
Once
more basically Class AB, but a method of dynamically boosting
power supply rails (as opposed to switching rails from Class G).
Boosting
voltage shall be made with a DC-DC converter.
It can be a Buck or Boost concerters, (buck is the most usual)
This
topology uses two +/- variable rails.
At low output levels, +/-VCC stay fixed let say +/- 10V.
Determined
by +10V reference and Vo sense, TMOS-P and TMOS-N maintain PWM at +/- 10V
regulated.
When the Driver reaches
10V (Reference) peak signal, Buck
converter follows driver voltage adding the signal over the 10v
Reference, then Sense terminals from PWM regulator increase the
output voltage to the collector of output transistors , like an envelope
voltage over the output signal. (see schematic)
In
this way power dissipation and efficiency are optimized when it
delivers more than 10V peak .
Class
H topology is basically a combination of Class A/B & Class D
topologies.
Advantages:
This
is perhaps the most efficient amplifier.
It can deliver the specified output power with a smaller
transformer and less heat-sink than conventional Class AB.
There
is no switching noise due to linear outputs.
Disadvantages:
Circuit
complexity increases, adding cost.
Poor
transient response.
EMI
filter in power supply is required, adding cost.
Conclusion:
Class
H topology is used in high efficient amplifiers, where the cost
is not an object.
