The primary IGBT transistors (Q1, Q2, Q3, Q4) are configured as an H-bridge circuit and switch the transformer
primary at high frequency and varying duty cycle.
Secondary output voltage from the transformer is rectified by the fast recovery diodes (D1, D2, D4, D5, D14-1,
D14-2) to DC then the DC voltage is connected to the welding output terminals. This DC voltage is controlled by the
PWM of the primary side IGBT transistors. The auxiliary inductor T2 provides the inductance to the weld current.
Two thermal overload devices are mounted in this inverter, a thermostat fixed to the IGBT heatsink and a NTC
Thermistor mounted in transformer T1. When an over temperature occurs, the control circuit inhibits the trig-
gering of the IGBTs which results in zero welding output. The yellow thermal overload indicator LED on the front
panel is illuminated.
The current transformer M1 provides a signal to the control circuit to indicate both transformer primary current,
and provides a voltage signal proportional to the output welding current to allow the control circuit to regulate
welding current.
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