20Ap1:4 Temperature Monitoring; 20Ap1:5 Shunt Input - ESAB OrigoArc 150 Service Manual

The pulse width modulator determines the frequency and pulse duration of the
switch transistors' control pulses. IC3 controls the pulse frequency, the pulse
time and inhibition of pulses.
The pulse frequency is 65 kHz +/--1 kHz, with a maximum pulse width of 42 --
44 % of the cycle width. See page 21 for screen traces of waveforms and
measurement instructions.
Transistor Q5 controls the primary winding of the pulse transformer on circuit
board 15AP1.
The reference voltage, +5.1 V, from IC3 is used as reference for the shunt
voltage and the current reference input.
20AP1:4 Temperature monitoring
The thermal overload switches, 15ST1 and 15ST2, are normally closed, which
means that input T2 is at about 9 V.
15ST2 opens at 85 _C, and is fitted on the heat sink. 15ST1 opens at 130 _C,
and is fitted in the winding of the main transformer, 15TM1.
If either of the switches operates, the power source is stopped and 1D2, the
yellow LED on the front panel lights. The power source cannot be restarted
until it has cooled sufficiently for the switch(es) to reclose.
20AP1:5 Shunt input
The shunt produces 60 mV at a welding current of 100 A. The shunt response
is linear to the welding current.
If the shunt is not connected to the circuit board, resistor R67 supplies about
0.6 to 0.9 V at the shunt input. This blocks the current control amplifier, i.e. the
machine does not deliver any welding current.
Note: the reference level for the shunt voltage is +5.
above are measured between terminals S1 and S2.
ch25d_20
1
- - 15 - -
V, voltages mentioned
Edition 040830