Section 7 − Theory Of Operation - Miller Millermatic 350P Technical Manual

SECTION 7 − THEORY OF OPERATION
.
Theory of Operation is shown for
the 200/230 volt models. Theory
for other models is similar.
1 Power Switch S1
Provides on/off control of welding
power source.
2 Input Rectifier SR1
Changes the AC line input power to
full-wave rectified DC.
3 Control Transformer T2
Supplies power to circuit boards.
4 IGBT Boards PC4, PC5
Provide interconnection of gate
pulses from PC1 to PM1 and PM2.
5 IGBT Power Modules PM1,
PM2
Use very fast on/off switching action
to effectively turn the DC into ac.
6 Interconnecting Board PC2
Provides electrical connections for
SR1, T1, C3, C4, L1, L3, L4, and
IGBT's. Precharge and bleeder
resistors are mounted on PC2.
7 Input Capacitors C3, C4
Filter the DC output voltage of SR1.
8 Inductors L1, L3, L4
L1 limits peak current in SR1, C3, and
C4. L3 and L4 limit voltage and cur-
rent in IGBT's during turn-on and
turn-off.
9 Gas Solenoid GS1
10 Control Board PC1
Controls weld output by changing
gate pulses (frequency of pulses) to
IGBT power modules PM1 and PM2
after comparing current or voltage
feedback to reference level set by
Control board PC1.
11 Input Contactor W1
Connects input power to intercon-
necting board PC2.
12 Fan Motor FM
Provides cooling of internal compo-
nents.
13 Relay CR1
Links auxiliary transformer according
to the input voltage.
14 Thermistor RT1
Protects output diodes D1 and D2
from overheating.
15 Thermistor RT2
Protects IGBT's PM1 and PM2 from
overheating.
TM-1327 Page 38
A. Block Diagram
1
Single-Phase
Power
or
Switch
Three-Phase
S1
Line Input
Power
CR1
3
Control
Transformer
T2
10
11 12
Input
Fan Motor
Contactor W1
7
Capacitors
W1
C3, C4
2 6
Input
Rectifier SR1
5
IGBT Power
Module PM1
4
IGBT Board
9
Gas Solenoid
GS1
Control
Board PC1
13 14
Relay CR1
FM
8
Input
Inductors
L1, L3, L4
Interconnecting
Board PC2
5
IGBT Power
Module PM2
4
IGBT Board
PC4 PC5
Gating Gating
Signals Signals
15
Thermistor Thermistor
RT1 RT2
Millermatic 350