Crown MARCO-TECH 5000VZ - Page 5

D506 is theflybackdiode forthe HS NPN output quadrant. In the event
that a back EMF (flyback) pulse exceeds power supply voltage, the
flyback diode will shunt this voltage to the supply in order to protect the
output devices.
PNP pre-drivers, drivers, output devices, and flyback diode D508 are a
mirror image of the NPN side.
Overall the High Side of bridge operates much like a conventional output
stage, but the Low Side (LS) is quite unique.
The LS senses output voltage and common (ground) buss potential.
The audio output is inverted by U503. Also in the U503 input circuitry
are static and dynamic balance controls. These controls provide a fine
balance of the grounded bridge. Output of the op-amp drives the LS pre-
driver circuits through the LS bias network.
LS bias ¡s controlled in a fashion similar to that of the HS. Two
transistors, Q529 and Q530, along fix LS bias voltage as measured from
pin 15(hot)topin13ofapplicableATEportTP1 orTP2. Potentiometer
R556 adjusts bias in the LS.
Diodes D504 and D505 control polarity of applied LS drive signal. Via
the bias transistors signal ¡s delivered to the bases of the pre-drivers
Q527 (NPN) and Q528 (PNP). Pre-drivers, drivers, and output devices
in the LS opérate class AB+B, exactly like the HS. The major difference
¡s that rather than driving a load, the NPN and PNP stages control the
ground reference for the high voltage rails. As the HS NPN's conduct,
LS PNP's conduct, and vice versa (as explained in section 4.2.1).
When the ODEP circuit senses that limiting drive is necessary to prevent
a dangerous thermal condition, ¡t provides an output which limits drive
Notes
+VCC1
OUTPUT POSITIVE SECTION
+VCC BUSS BAR
+ LVA
H-VCC1
Q513 Q515 Q517 Q536 '
C5O6
220pF _L C510
' O.O1
D5O6
High Side Predrivers,
Drivers, Output Devices,
and Flyback Diodes.
Notice the various sense
lines. These are used
for various functions
such as VZ switching
sense and protection
features.
MA-5000VZ - 5