V300-I
THEORY OF OPERATION
OUTPUT AND CONTROL CIRCUITS
The AC output of the transformer is changed to DC by
the Output Rectifier. The Output Choke between the
negative side of the rectifier and the negative output
stud provides the necessary filtering for DC welding.
The two smaller chokes and their series diodes are the
OCV boost circuit used to help provide good weld
starts.
Current feedback to the Control Board is provided by
the shunt in the negative output circuit. It is used for
weld control, overcurrent protection and actual amme-
ter readings. The Voltage feedback lead at the positive
output stud also provides information for weld control
and actual voltmeter readings.
The Control Board monitors input from the front panel
controls (output, arc control, mode switch, etc..). The
software on the board processes these inputs, sets up
the proper weld information and sends the “set” para-
meter information to the meter.
When weld output is requested, the Control Board
compares the input information to the feedback signals
and provides the correct PWM signals to the Switch
Boards for optimum welding. The Mode Switch setting
determines which feedback signal (voltage or current)
will have the most relevance. However, both signals
are used in all modes.
The Control Board also monitors signals from the ther-
mostats and the Protection Board and if necessary,
shuts off the weld output. The protection circuit infor-
mation is discussed in more detail later in this section.
E-5 E-5
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