Lincoln Electric INVERTEC SVM101-B Service Manual page 25

E-3
1ø OR 3ø DETETCTION (H5)
INPUT
LINE
RECTIFIER
SWITCH
1 AC1
2 AC2
3 AC3
3A
A-LEAD
24VDC
AUXILIARY
FAN
TRANSFORMER
18VAC
24VAC
TO
WIREFEEDER
PRECHARGE & PROTECTION CIRCUITS
The DC voltage from the Input Rectifier is applied to the
Driver Board to begin charging the Switch Board
capacitors at a slow rate. When the pre-charge level is
achieved, the input relays close, applying the full DC
voltage to the capacitors. Depending on the Code
Number of the machine, there will be either two or four
relays and they may or may not be mounted on the
Driver Board.
The Driver Board is also responsible for gating the
Field Effect Transistors (FETs) on the Switch Boards,
as directed by the pulse width modulated (PWM) signal
from the Control Board.
The Protection Board monitors the capacitors for prop-
er balance and voltage level. If an imbalance or over-
voltage condition is detected, the Protection Circuit will
de-energize the relays, removing the power from the
switch circuits. The machine output will also be dis-
abled.
NOTE: Unshaded areas of block logic diagram are the subject of discussion
THEORY OF OPERATION
FIGURE E-3 ---PRECHARGE & PROTECTION CIRCUITS
POWER SWITCH
SECTIONS
20KHZ
LEFT SWITCH BOARD
FET MODULES
FET MODULES
PRE-CHARGE
DRIVER
BOARD
CR1
PROTECTION
PULSE
BOARD
TRAIN
CR2
PRE-CHARGE
RIGHT SWITCH BOARD
2ND STEP PWM
FET MODULES
POWERBOARD
FET MODULES
<1 VDC
LOCAL
METER MODE
REMOTE
1ST STEP PWM VOLTAGE
15VDC-CONTROL BOARD FUNCTION VOLTAGE
24VAC-THERMOSTATS-GUN TRIGGERING
V300-I
MAIN
TRANSFORMER
CAP
CURRENT
TRANSFORMER
CONTROL
BOARD
BOTTOM
Y-Y FEEDBACK
CAP
VOLTAGE FEEDBACK
POT
POT
CURRENT FEEDBACK-PROTECTION
Another function of the Protection Board is to detect
whether the input voltage is single phase or three
phase and pass that information to the Control Board.
The maximum output of the machine will be limited to
approximately 250 amps with single phase input and
360 amps with 3 phase input.
RECTIFIER
CHOKE
HEATSINK
TOP
1 DIODE
5 DIODES
5 DIODES
TOP
1 DIODE
CHOKE
CHOKE
SHUNT
E-3