Crown MARCO-TECH 5000VZ User Manual page 9

to switch VZ modes. The switching circuitry is designed to prevent
audible switching distortion to yield the highest dynamic transfer
function—you hear only the musió and not the amplifier. You get not
only the máximum power with the máximum safety, you also get the best
power matching to your load.
Actual current flow with power supply and grounded bridge operating
together is shown on the previous page.
The individual components are shown below. Upstream of the toroid
transformer, though not shown, is where shutdown protection and soft-
start circuitry taps in to control AC mains ¡nput to the power supply. The
VZ Control circuitry senses audio level and switches the articulating VZ
supplies to either parallel (high current) mode for lower level audio, or
series (high voltage) mode for high program peaks.
Notes
Toroid Bridge 1
In both examples it can be seen that when the MOSFET switch is off,
the dual supplies are torced to opérate ¡n a parallel mode. Audio level
is sensed via a line tapping off the NFb loop. When audio level ¡s rising
and at about 80% of the parallel mode supply voltage, the MOSFETs
(the switch is actually a three-device composite switch) are turned on.
No current will flow through either of the control diodes (D810 and D811,
as shown for channel 1) because reverse polarity is applied through the
MOSFET switch. Since this happens to both rectifier sources at the
same time, and the negative side of Bridge 1 ¡s then shorted to the
positive side of Bridge 2, the supplies are forced to opérate in series
mode. Like two batteries, the supplies will provide double voltage in
series mode, double current ¡n parallel mode.
Although shipped from the factory ¡n normal VZ mode, the user may
switch modes to lock low voltage (high current), lock high voltage, or
opérate the supply in Bi-ODEP mode. Bi-ODEP is similar to normal VZ
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