Power Pc Board Over Current Protection (0558038315) - ESAB Powercut 1600 Service Manual

SECTION 4 DESCRIPTION Of OPERATION

4.10.4 Power PC Board Over Current Protection (0558038315)

The power board uses a pair of current transformers to detect an over current condition on the output of
the PC1600. In the event the output exceeds the rated current, the induced signal in the transformers shuts
down the power circuit at the control board microcontroller.
The output from each of the IGBTs is passed to the output transformer through the Current Transformers L1
and L2. The output of these transformers is rectified and then connected to a buffering IC. When the output
of this op amp exceeds the error threshold, the control board micro shuts down the PWM and sends an er-
ror to the display.
When the PC1600 is operating, current flowing out of Q101 to the output transformer flows through a wire
that passes through the Current Transformer L2. The expanding and contracting magnetic field of the wire
induces a voltage in the Current Transformer. The output of this transformer is connected to a full wave
bridge, D12, where it is rectified and passed to op amp U10A on pin 3 for buffering. The output of U10A on
pin 1 passes through D10 and is sent to the main control board PCB1 as signal bridge_peak. When this
voltage exceeds 2.75 VDC the main control board PCB1 will shut down the PWM and send an error to the
display.
When the PC1600 is operating, current flowing out of Q102 to the output transformer flows through a wire
that passes through the Current Transformer L1. The expanding and contracting magnetic field of the wire
induces a voltage in the Current Transformer. The output of this transformer is connected to a full wave
bridge, D14, where it is rectified and passed to op amp U11B on pin 5 for buffering. The output of U11B on
pin 7 passes through D15 and is sent to the main control board PCB1 as signal bridge_peak. When this
4.10
voltage exceeds 2.75 VDC the main control board PCB1 will shut down the PWM and send an error to the
display.
It should be noted that the 2.75 VDC is the greater of the two outputs of the current transformers. If either
one of them puts out a signal greater than 2.75 volts DC, the PWM circuit will shut down. These two signals
are compared and the greater of the two is present at R73 before passing to the main control board.
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