Circuit
Full-bridge MOSFET inverter power stage
DC bus, switch groups, blocking capacitors, transformer drive and secondary rectifier flow.
Power-stage purpose
The full-bridge MOSFET inverter stage converts the high-voltage DC bus into high-frequency AC for the main transformer. In many ZX7-style machines this stage includes MOSFET groups, blocking capacitors, current transformer feedback, snubbers and the primary of the main transformer.
Simplified flow
+530V DC bus
↓
Full-bridge MOSFET groups
↓
Blocking capacitors
↓
Main transformer primary
↓
Secondary rectifier board
↓
Output inductor / shunt
↓
Welding output
Failure modes
- MOSFET short due to bad gate drive.
- Blocking capacitor failure.
- Current transformer or feedback path abnormal.
- RC snubber open or burnt.
- Main transformer primary fault.
- Secondary rectifier short overloading primary.
Before replacing MOSFETs
Check driver waveform, gate resistors, snubber parts, transformer condition and secondary rectifier board. A shorted secondary stage can destroy a new primary switch set.