INVERTEC V300-I
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E-4
THEORY OF OPERATION
GENERAL DESIGN
CONSIDERATIONS
FET semiconductors are well suited for
operating at high frequencies. This is the
primary reason that Lincoln’s Invertec
design uses FETs instead of Silicone
Controlled Rectifiers (SCRs) or bipolar tran-
sistors for power switching. This high-fre-
quency switching is not detectable to the
human ear. Annoying switching sounds that
are typical to lower frequency inverter
power supplies are not present in the
Lincoln high frequency inverter design.
Unlike conventional transformers, this
design is small, lightweight, and capable of
operating at high frequencies without over-
heating. Future designs will also use newer
high-speed IGBTs in place of FETs.
OUTPUT RECTIFICATION AND
WELDING CONTROL
The AC output from the main transformer
secondary is rectified to a DC output.
Output voltage and current (feedback) sig-
nals are taken at the output terminals and
fed to the Control Board. The Control Board
also monitors the panel controls to deter-
mine which weld process is being employed
and how the output should be controlled to
optimize welding results. The Control Board
controls the FET switching through pulse
width modulation circuitry. See FET discus-
sions Figures E.5 and E.6.
Excessive output current, the thermal pro-
tection signal, and the overvoltage signal
are monitored by the Control Board for the
trigger disable function.
1ø OR 3ø DETETCTION (H5)
LINE
SWITCH
INPUT
RECTIFIER
AC1
AC2
AC3
A-LEAD
AUXILIARY
TRANSFORMER
TO
WIREFEEDER
18VAC
24VAC
POWERBOARD
24VDC
PRE-CHARGE
2ND STEP PWM
1ST STEP PWM VOLTAGE
15VDC-CONTROL BOARD FUNCTION VOLTAGE
24VAC-THERMOSTATS-GUN TRIGGERING
LOCAL
REMOTE
METER MODE
POT
POT
<1 VDC
FAN
1
2
3
CONTROL
BOARD
Y-Y FEEDBACK
3A
POWER SWITCH
SECTIONS
20KHZ
PULSE
TRAIN
DRIVER
BOARD
PRE-CHARGE
CR1
CR2
PROTECTION
BOARD
TOP
TOP
LEFT SWITCH BOARD
FET MODULES
CAP
FET MODULES
MAIN
TRANSFORMER
RIGHT SWITCH BOARD
FET MODULES
CAP
FET MODULES
BOTTOM
1 DIODE
5 DIODES
5 DIODES
1 DIODE
CHOKE
SHUNT
RECTIFIER
HEATSINK
CHOKE
CHOKE
CURRENT
TRANSFORMER
VOLTAGE FEEDBACK
CURRENT FEEDBACK-PROTECTION
FIGURE E.4— OUTPUT CIRCUITS.
NOTE: Unshaded areas of block logic diagram are the subject of discussion.
