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THEORY OF OPERATION
E-4 E-4
POWER MIG 300
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INPUT RECTIFIER, CHOPPER
ASSEMBLY AND FEEDBACK
The 60 VAC output from the main transformer sec-
ondary is connected to an input rectifier. The resultant
80 VDC is applied to four parallel capacitors incorpo-
rated within the Chopper Assembly. These capacitors
function as filters and also as power supplies for the
insulated gate bipolar transistors or IGBT. See IGBT
Operation in this section. The IGBT acts as a high-
speed switch operating at 20KHZ. This device is
switched on and off by the Weld Control Board through
pulse width modulation circuitry. See Pulse Width
Modulation in this section. This "chopped" DC output
is applied through an output choke coil to the positive
output terminal and through a current transducer to the
negative output terminal. The choke functions as a
current filter. A free-wheeling diode is incorporated in
the Chopper Assembly to provide a current path for the
stored energy in the choke when the IGBT is turned off.
See Chopper Technology Fundamentals in this sec-
tion.
Output voltage and current feedback information is fed
to the Weld Control Board. This information is sensed
from the current transducer and voltage sense circuitry
on the output terminal circuits. If current or voltage
become abnormally high, the Weld Control Board will
shut off the IGBTs, thus disabling the machine's output.
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
FIGURE E.4 – DIODE CONTROL RECTIFIER AND POWER BOARD
IGBT
+
LINE
SWITCH
RECONNECT
PANEL
MAIN
TRANSFORMER
RELAY
SPOOL
GUN
BOARD
FEEDER
BOARD
MSP
BOARD
ENCODER
BOARD
DISPLAY
BOARD
RS232
CONNECTOR
WELD CONTROL BOARD
SPOOL GUN
PUSH-PULL
SWITCH
WIRE DRIVE
MOTOR
OUTPUT
RECTIFIER
CHOPPER
ASSEMBLY
OUTPUT
CHOKE
CURRENT
TRANSDUCER
GUN
POS
OUTPUT
TERMINAL
NEG
OUTPUT
TERMINAL
POWER
BOARD
DIODE CONTROL
RECTIFIER
FAN
MOTOR
FOOT AMPTROL OR REMOTE (6-PIN AMPHENOL)
SPOOL GUN OR PUSH-PULL GUN (7-PIN AMPHENOL)
GAS
SOLENOID
SEC
THERMOSTATS
_
+
115
VAC
30
VAC
60
VAC
80
VAC
40 VDC
40
VDC
40 VDC
24 VDC
20 VDC
PWM
SIGNALS
+15/-15/+5 VDC
SHIELDED
CABLE
GUN TRIGGER AND THUMB SWITCH
SHIELDED CABLE AND SPI COMMUNICATIONS
ARCLINK
+5 VDC
CURRENT
FEEDBACK
VOLTAGE
FEEDBACK
FROM WELD
CONTROL BOARD
TO FAN RELAY
IGBT
DRIVE
T
A
C
H
CHOPPER
(Below code 10900)
Mechanical Encoders
(Above code 10900)