THEORY OF OPERATION | ||
| FIGURE E.3 – SWITCH BOARD & MAIN TRANSFORMER |
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| Main Switch Board | |
Input switch | Input | Primary | |
Rectifier | |||
Current | |||
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| Reconnect | |
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| Fan |
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| 115VAC Fan Supply | rolnto Cn | Primary Current Feedback(2) | IGBDriveT | |||||||||
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| Auxiliary | Input Relay Control |
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| Soft Start Control |
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| Transformer |
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| Fa | V/F Capacitor Feedback (2) |
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| 220 VAC |
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w |
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| 40VDC |
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| Power | +15VDC, |
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4 | 220 |
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| Can Supply +5VDC |
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5 | Receptacle | 65VAC |
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SWITCH BOARD &
MAIN TRANSFORMER
To Control
Board
Feedba c | Curre nt |
k |
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Choke
See sen
O tu up Vt golta
21 Lead
Voltage
Sense
Recp.
Positive
Output
Terminal
Negative
Output
Terminal
Yellow
Thermal
LED
Status
Red/Green
LED
R232
Connector
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There is one switch board in the POWER WAVE 355M/405M. This board incorporates two pairs of input capacitors, two insulated gate bipolar transistor (IGBT) switching circuits, a fan motor drive circuit, and a voltage/frequency capacitor feedback circuit. The two capacitors in a pair are always in series with each other. When the reconnect switch is in the lower volt- age position the capacitor pairs are in parallel - that is, two series capacitors in parallel with two series capac- itors. When the reconnect switch is in the high voltage position the two capacitor pairs are in series or, four capacitors in series. This is required to accommodate the higher input voltages.
When the input capacitors are fully charged they act as power supplies for the IGBT switching circuits. When welding output is required the Insulated Gate Bipolar Transistors switch the DC power from the input capacitors, "on and off" thus supplying a pulsed DC current to the main transformer primary windings. See IGBT Operation Discussion and Diagrams in this section. Each IGBT switching circuit feeds current to a separate, oppositely wound primary winding in the main transformer. The reverse directions of current flow through the main transformer primaries and the offset timing of the IGBT switching circuits induce an
AC square wave output signal at the secondary of the main transformer. The two current transformers (CT) located on the switch board monitor these primary currents. If the primary currents become abnormally high the control board will shut off the IGBTs, thus dis- abling the machine output. The DC current flow through each primary winding is clamped back to each respective input capacitor when the IGBTs are turned off. This is needed due to the inductance of the transformer primary winding. The firing of the two switch boards occurs during halves of a 50 microsec- ond interval, creating a constant 20 KHZ output. In some low open circuit Tig modes the firing frequency is reduced to 5KHZ.
The POWER WAVE 355M/405M has a F.A.N. (fan as needed) circuit. The fan operates when the welding output terminals are energized or when a thermal over temperature condition exists. Once the fan is activat- ed it will remain on for a minimum of five minutes. The fan driver circuit is housed on the switch board but it is activated by a signal from the control board.
NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion
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