Service manual

Edition 101222
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s1Cad160
PFC control is built on the specialised integrated circuit IC3. PFC control senses
the DC bus voltage, input current (5,6 CN1) and input voltage, providing the
constant 390...400V on the DC bus along with sinusoidal form of the input current.
This goal is achieved by the control of the switch in the boost converter placed on
the power PCB. Actually, the control circuit placed on the control PCB produces the
drive signal for PFC switch.
Specialised PFC controller (IC3), used in the present solution, does not provide
overvoltage protection. Therefore, extra two comparators were applied to control
the DC bus voltage. There is a two--step overvoltage protection. First, on the lower
level simply cuts off the drive signal from the PFC control IC by means of the logic
AND gate.
Second level is higher the first, and it resets the PFC control IC via it’s soft start
input.
The system of overvoltage protection is needed especially for work with engine
driven generator, where the voltage surges occur at the end of the welding.
AP2:2H. Auxiliary power supply
The auxiliary power supply provides power for primary and secondary control
circuits. Basically it produces +15V supply for the primary circuits and galvanically
separated +24V supply for secondary circuit. In addition it provides firing pulses to
the thyristor in the input rectifier.
The auxiliary power supply is switched off by means of the voltage control circuit
(HV_ENABLE). Therefore thyristor firing pulses are not delivered until DC bus
capacitors are charged to the peak input voltage.