Lincoln Electric INVERTEC 270SX Service Manual page 14

INVERTER SECTION AND MAIN TRANSFORMER
Inverter and Main Transformer
When the input filter capacitors are fully charged they
act as power supplies for the IGBT switching circuit.
The IGBT switch the DC power from the input
capacitors "on and off," thus supplying pulsed DC
current to the main transformer primary windings.
The full bridge inverter switching frequency is 25KHz.
Current transformer located on the inverter board
monitor the primary current. If the primary current
become abnormally high, the inverter control circuit
will shut off the IGBTs, thus disabling the machine's
output. A thermal protector is also present, to the
inverter heatsink, to protect the IGBTs from
overheating conditions.
The main transformer insulate the primary circuit from
the secondary circuit; this secondary winding supplies
the electrode-to-nozzle and electrode-to-work voltages
and the resulting currents. This high current winding is
capable of supplying maximum output current during
the cutting process.
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