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E-2

E-2

THEORY OF OPERATION

FIGURE E.2 – INPUT VOLTAGE

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S

FET

B

W

O

I

CAP

A

T

R

C

FET

H

D

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PRE -

 

 

LINE

 

INPUT

 

 

 

 

 

CHARGE

 

 

SWITCH

 

RECTIFIER

 

 

R

P

 

D

B

 

 

 

 

 

 

 

 

 

 

 

 

E

 

 

 

 

 

 

 

 

 

 

 

CR1

 

R

B

R

 

 

 

 

 

 

 

 

 

 

 

C

O

O

 

 

 

 

 

 

 

 

 

 

 

 

O

T

O

I

A

 

 

 

 

 

 

 

 

 

 

 

 

N

E

A

V

R

 

 

 

 

 

 

 

 

 

 

 

 

C

 

 

 

 

 

 

 

 

 

 

 

 

N

T

R

E

D

 

 

 

 

 

 

 

 

 

 

 

 

E

I

D

R

 

 

 

 

 

 

 

 

 

 

 

 

O

 

 

 

 

 

 

 

 

 

 

 

 

 

C

N

 

 

 

 

 

 

 

 

"A"

 

 

 

T

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

LEAD

 

CR2

 

 

 

 

PRE -

FAN

 

 

 

 

 

 

 

 

18

S

 

B

 

CHARGE

 

 

 

 

 

 

 

 

P B

 

 

 

 

 

 

TRANS

 

VAC

FET

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

T1

 

 

O O

W

 

O

 

 

 

 

 

 

 

 

 

 

 

 

 

W A

I

CAP

A

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

115

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

E R

T

R

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

VAC

2

C

 

 

 

 

 

 

 

 

 

 

 

 

 

4

R D

FET

 

 

 

 

 

 

 

 

 

 

 

 

 

V

 

H

D

 

 

 

 

 

TRANS

 

 

A

 

 

 

 

 

 

 

 

 

 

 

C

 

 

LESS THAN 1VDC

 

 

 

 

 

T4

 

 

 

 

 

T

 

 

PULSE TRANSFORMER SIGNAL

 

 

 

 

 

 

 

 

 

H

 

 

 

 

 

 

 

 

 

 

 

 

 

E

 

 

 

 

 

 

 

RPWM SIGNAL

M

O

S15VDC

T

A

 

 

T

GUN TRIGGER

CONTROL BOARD

 

 

36VAC

TAILOUT

PEAK

BACK-

PEAK

HOT

BACK-

WIRE

CURRENT

GROUND

SIZE

CONTROL

CURRENT

START

GROUND

(STT II ONLY)

METER

METER

CONTROL CONTROL CONTROL

SWITCH

CURRENT

TRANS

T3

WIRE

TYPE

SWITCH

 

 

POSITIVE

 

 

 

 

OUTPUT

 

 

 

 

TERMINAL

 

 

MAIN

1 OHM

 

 

 

TRANSFORMER

 

 

 

T2

 

 

 

 

CURRENT

IGBT

NEGATIVE

 

 

SENSOR

MODULE

OUTPUT

 

 

 

 

TERMINAL

 

 

CHOKE

 

R

 

VOLTAGE

 

 

 

 

 

E

 

SENSING

 

 

 

RECEPTACLE

 

 

M

 

 

 

 

 

 

D

O

 

 

 

T

 

 

 

R

 

REMOTE

 

I

E

B

 

V

 

CONTROL

 

 

 

RECEPTACLE

 

E

P

O

 

S

R

A

 

 

I

O

R

 

 

G

T

 

 

N

D

 

 

E

 

 

A

 

 

 

L

C

 

 

 

 

T

 

WIRE

 

 

I

 

FEEDER

 

 

O

 

RECEPTACLE

 

 

N

 

 

CURRENT FEEDBACK

IGBT

DRIVER

BOARD

VOLTAGE FEEDBACK

10VAC AND 6VAC

42VAC

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GENERAL DESCRIPTION

The Invertec STT is a 225 ampere, inverter based, arc welding power supply specifically designed for the Surface Tension Transfer (STT) welding process. It cannot be classified as either a constant current (CC) or a constant voltage (CV) machine. The STT pro- duces current of a desired waveform to reduce spatter and fumes. The STT process is optimized for short - circuit GMAW welding only.

INPUT VOLTAGE

The Invertec STT can be connected for a variety of three-phase voltages. The initial input power is applied to the STT through a line switch located on the front of the machine. The AC input voltage is applied to the input rectifier and the T1 auxiliary transformer. The T1 transformer develops the appropriate AC voltages to operate the cooling fan, the power and control boards. The T1 transformer also supplies primary voltage to the T4 auxiliary transformer as well as 42 VAC to an exter- nal wire feeder. The T4 transformer supplies power to the IGBT drive board and the control board.

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NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.

INVERTEC STT

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Lincoln Electric SVM129-B service manual Theory of Operation, General Description, Input Voltage