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THEORY OF OPERATION
E-2 E-2
PRECISION TIG® 225
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GENERAL DESCRIPTION
The PRECISION TIG® 225 is a member of our field
acclaimed PRECISION TIG® family of industrial arc
welding power sources. Premium features include:
1. Precise constant current output.
2. Full range square wave AC/DC TIG (GTAW)
welding.
3. Enhanced version of the patented MicroStart
TM
Technology for its lower Minimum (5amps) to high-
er Maximum (225 amps) output control range.
4. Built-in high frequency stabilization for DC TIG
starting and continuous AC TIG welding.
5. AC/DC Stick (SMAW capability.)
FIGURE E.2 - General Description & Input Power Circuit
INPUT POWER CIRCUIT
The desired single-phase input power is connected to
the TIG 225 through an input power switch located in
the front panel of the machine. The machine can be
configured for either 230VAC or 208VAC input voltage
by connecting the appropriate lead (H2 or H3) to the
input power switch. When the input power switch is
turned “ON” the input voltage is applied directly to the
primary of the main transformer.
The main transformer changes the high voltage, low
current input power to a low voltage, high current out-
put which is available at the main secondary winding
(X1 and X2). In addition three auxiliary windings are
incorporated in the main transformer. The 115VAC
winding supplies power to the fan motor, the 115 VAC
receptacle, and also, through the control board, pow-
ers the gas solenoid valve and the high voltage trans-
former. The 18VAC winding provides power to the trig-
ger circuitry. The other 18VAC winding is rectified and
regulated to a 15VDC supply which operates the cir-
cuitry on the control board.
NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion
INPUT
POWER
SWITCH
MAIN
TRANSFORMER
POLARITY
SWITCH
SCR
BRIDGE
X1
X2
AC
AC
DC+
DC-
CONTROL
BOARD
18VAC
18VAC
115VAC
FAN
REMOTE
RECEPTACLE
H1
H2
H3
SHUNT
115VAC
HIGH VOLTAGE
TRANSFORMER
CIRCUIT
BY-PASS
BOARD
HI-FREQUENCY
TRANSFORMER
C
H
O
K
E
WORK
ELECTRODE
THERMAL
LIGHT
GAS
VALVE
THERMO-
STATS
OUTPUT
CONTROL
MODE
SWITCH
POWER
"ON"
DIGITAL
DISPLAY
F
E
E
D
B
A
C
K
AUTO
BALANCE
LED
TIG
LED
STICK
LED
PULSE
FREQ.
LED
BYPASS
ASBLY
AC
BALANCE
CONTROL
PULSE
CONTROL
POSTFLOW
CONTROL
115 VAC
Receptacle
Circuit Breaker
Protected