Vz Supply Circuitry - Crown MARCO-TECH 5000VZ User Manual

VZ SUPPLY CIRCUITRY
For simplicity, only channel 1 circuitry will be covered unless noted
otherwise. Circuitry.forthe VZ supply (and lowvoltage supply) is located
on the control module. The actual VZswitch circuit is located on the VZ
switch assembly. In this assembly are the two bridge rectif ¡ers, two f ilter
capacitors, MOSFET switches, and control diodes D810 and D811.
Three MOSFETs are used in parallel for sharing the high currents
supplied to the rails.
WARNING: From a sen/ice standpoint, ' r t is critical to note that VZ
switch control circuitry is NOT ground referenced. Any attempt to take
voltage measurements using a ground reference when voltage ¡s
applied will not only be unreliable, but may be extremely dangerous.
Serious damage to equipment or personnel may occur ¡f this is
attempted.
The output of a 555 timer (U703) on the control module determines
whether the MOSFETs are switched on (high) or off (low). This 555
device and the various sources that feed the 555 are the things that
make the articulation work wfíéh and how desired.
The master 555 trigger is controlled by the output of U702A. S700,
physically accessible from behind the front grille, determines the VZ
operating mode. In high voltage mode the output of U702A ¡s held low.
This in turn keeps the 555 output high and the MOSFETs are kept on.
In the high current mode U702A is held ¡n the opposite polarity keeping
the output of the 555 low and the MOSFETs off. In the AUTO position
of S700, the audio level sense circuitry controls the threshold and reset
inputs to the 555. The 555 will then switch states to high voltage when
the audio level is sufficient and will switch back down automatically when
Notes
Low Voltage Power Supply,
including DC Pulse network
for Soft-start and Fan Control
circuitry.
MA-5000VZ - 11