Thermal Protection - Lincoln Electric SQUARE WAVE TIG 255 SVM100-A Service Manual

- THEORY OF OPERATION SECTION -
Theory of Operation Section...........................................................................Section E
Power Supply Operation ...............................................................................E-1 - E-5
Input Line Voltage and Main Transformer.......................................................E-1
Output Rectification and Feedback Control ....................................................E-2
High Voltage / High Frequency Circuit ............................................................E-3
DC Welding Output .........................................................................................E-4
AC Welding Output .........................................................................................E-5
SCR Operation.......................................................................................................E-6
Thermal Protection .................................................................................................E-7
LINE
MAIN
SWITCH
TRANSFORMER
R
E
C
O
N
N
E
C
T
POWER
FACTOR
CAPACITORS
115VAC
FAN
115 VAC
RECEPTACLE
RECEPTACLE
NOTE: On subsequent pages areas of this diagram that are the topic of discusstion are shown in white, other
portions of the circuit are shaded.
TABLE OF CONTENTS
POWER SUPPLY BLOCK LOGIC DIAGRAM
POLARITY
SWITCH
AC DC+
X2
SCR
BRIDGE
X1
AC DC-
ARC START
115 VAC
PROTECTION
SNUBBER
GATE SIGNALS
BOARD
HI-FREQ
115 VAC
CONTROL
TRANSFORMER
115 VAC
REMOTE
BY-PASS
BOARD
SHUNT
CHOKE
CONTROL
BOARD
24 VAC
18 VAC
16 VAC
HIGH VOLTAGE
HIGH FREQUENCY SPARK
TRANSFORMER
CIRCUIT
Section E
WORK
HI-FREQ
TRANSFORMER
ELECTRODE
LCD DISPLAY
KEYPAD
LED
BOARD
KEYPAD
SQUARE WAVE TIG 255