ESAB LTR 160, Service Manual

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cltr0de2
1. Gas pre--flow.
2. Open--circuit voltage LTR 160: 65--80 V; LTR 200: 72--82 V.
Contact with the workpiece causes the control amplifier to generate a sensing
current, which is limited to 8 A.
3. When the electrode is lifted from the workpiece and the arc voltage exceeds
5 V, the control amplifier generates an elevated starting current for about 50 ms.
The starting current is 20 A higher than the set value of current.
4. Welding is performed at the set value of current.
10 Gate circuit
The pulse width modulator IC13 determines the frequency and pulse time of the
MOSFET transistors’ control pulses.
It is important that the frequency and maximum pulse time are within the specified
tolerances. The pulse frequency is 36.5
¦
0.5 kHz and the maximum pulse time is
41%
¦
1.5% of the cycle time.
Maximum pulse time results in maximum current and voltage.
IMPORTANT
The frequency and pulse time are very important parameters. If they are
incorrect, they can result in transistor failure in the main circuit.
See also CHECKING THE GATE PULSES on next page.
The MOSFET transistors’ drive stage produces control pulses for the gate--source on
the power transistors. There is a separate output for each switch unit.
All gate circuits are galvanically isolated from other circuits on the board. The
insulation voltage between the pulse width modulator and the gate circuits is 4 kV.
WARNING! The gate circuits are at mains voltage.