Dc Welding Output - Lincoln Electric PRECISION TIG 375 Service Manual

E-5
CONTROL
OPTIONAL POWER
FACTOR
CORRECTION
CAPACITORS
POWER
SWITCH

DC WELDING OUTPUT

When the polarity switch is placed in either DC position, the
AC voltage from the main transformer secondary is applied
to the SCR bridge. The SCR bridge and choke circuits are
connected in the conventional full wave bridge and filter
configuration, resulting in a controlled DC output. Since
the choke is in series with the negative leg of the bridge
and also in series with the welding load, a filtered DC is
applied to the output terminals. The bypass board protects
the internal circuitry from interference.
FIGURE E.6 DC WELDING CURRENT GENERATION
PRIMARY
10
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
THEORY OF OPERATION
FIGURE E.5 – DC WELDING OUTPUT
Precision Tig 375
BACKGROUND
CIRCUIT
FROM
BOARD
STICK OCV BOOST
CIRCUIT
FROM CONTROL BOARD
X1
X3
X2
115 VAC
115 VAC
20 VAC
20 VAC
MINIMUM
OUTPUT
CONTROL
MAXIMUM
OUTPUT
CONTROL
G
PRECISION TIG 375
REAR GANG
POLARITY
SWITCH
BYPASS
AC DC
SCR
BRIDGE
AC DC
SHUNT
GAS
THERMOSTAT
FANS
SOLENOID
CONTROL BOARD
ADVANCED CONTROL
PANEL RECEPTACLE
PROTECTION STICK
METER
BOARD TIG
SWITCH
BALANCE POST
CONTROL
FLOW
REMOTE
RECEPTACLE
When the machine is in the DC mode, the background cir-
cuitry provides an add boost voltage to the output termi-
nals. This circuitry is controlled by the control board.
G
G
G
WORK
BOARD
FRONT
ELECTRODE
HIGH FREQUENCY
TRANSFORMER
REAR
ELECTRODE
HIGH FREQUENCY
INTENSITY ADJUSTMENT
HIGH VOLTAGE
TRANSFORMER
THERMOSTATS
LED's
LOCAL/REMOTE
SWITCH
CHOKE
ELECTRODE
WORK
E-5
DC