About Grounded Bridge Amplifiers - AE Techron LV 3620 Operator's Manual

4.2 About grounded bridge amplifiers

The patented four-quadrant topology used in the grounded output stages is
called the grounded bridge. The grounded bridge topology takes full
advantage of the power supply by delivering to the load, peak-to-peak
voltages that are twice the voltage seen by the output transistors and twice
the voltage generated by the power supplies. See Illustration 4–1.
To achieve the required output current, several high power transistors are
combined to function as composite NPN and PNP transistors. Each output
stage has two composite NPN and two composite PNP devices.
Since the output stages are constructed with bipolar transistor devices, the
preferred and more descriptive terminology is to name an output stage in
terms of whether the stage acts as a NPN or PNP stage and whether it is on
the high (output) side of the load or low (ground) side of the load.
Positive current is delivered to the load by increasing conductance
simultaneously in the high-side NPN and low-side PNP stage, while
decreasing conductance of the high-side PNP and low-side NPN in synchrony.
For a negative output current, the roles of the quadrants are reversed with
the low-side NPN and high-side PNP quadrants carrying the negative peak
output current.
A wide-bandwidth multi-feedback loop design is used for state-of-the-art
compensation. This produces ideal behavior and results in ultra-low distortion
values.
Hi NPN
Interbase
E in
bias
voltage
Hi PNP
Illustration 4–1 Ground bridge amplifier output stage topology
Principles of Operation
LV 3620
Lo NPN
Interbase
bias
Load
voltage
Vcc
supply
Lo PNP
E' in
4–2