Circuit
Soft-Switching Inverter Arc Welder Main Loop
Phase-shift full-bridge, resonant-capacitor and saturable-inductor reference for soft-switching inverter arc welders and repeated IGBT failure diagnosis.
Database summary
A soft-switching inverter arc welder uses the energy in leakage inductance, resonant capacitors and controlled phase shift to reduce switching stress in the bridge. In a repair database this matters because a repeated IGBT or MOSFET failure may be caused by the commutation network, not by a defective replacement device.
This WelderData reference covers an improved phase-shift full-bridge arc-welding power source. It is written as a repair interpretation page, not as a design-calculation manual.
Functional main-loop map
Main sections to separate
| Section | Repair interpretation | Why it matters |
|---|---|---|
| Phase-shift full bridge | Q1/Q3 are treated as the leading arm; Q2/Q4 are treated as the lagging arm. | The two arms do not fail under exactly the same commutation conditions. |
| Commutation capacitors | C1/C3 and C2/C4 shape switching transitions and reduce device stress. | A failed or changed capacitor can turn a soft-switching condition into hard switching. |
| CX circulating-current capacitor | Series capacitor used to limit or shape circulating current. | Wrong value, leakage or open condition changes light-load and no-load behavior. |
| LX1 leakage inductance | Transformer equivalent leakage inductance participates in commutation energy. | Transformer replacement, wiring layout or primary loop changes can change switching stress. |
| LX2 saturable inductor | Used to improve lagging-arm zero-current or transition behavior. | Heating, shorted turns or saturation drift can create repeated device failure. |
| UC3846 current-mode control | Peak-current control is used to protect switches and help prevent transformer bias. | A control failure can look like a power-stage fault if feedback and current limit are not separated. |
No-load and light-load repair warning
Soft switching is easiest to maintain when enough commutation energy is available. No-load and light-load operation can be the difficult region: reactive current may be insufficient, commutation may fail, and a bridge device may see a hard turn-on or hard turn-off condition.
For repair work, this means an inverter can destroy devices even when it is not welding at high current. If a repeated failure occurs during idle, arc-start or low-output testing, inspect resonant capacitors, saturable inductors, driver timing, dead-time behavior and transformer primary-loop evidence before installing another IGBT.
Repair checklist for repeated power-device failure
| Evidence | What to check | Do not conclude |
|---|---|---|
| Replacement IGBT fails immediately | Gate drive, resonant capacitors, leakage/saturable inductor and DC bus path. | Do not call it a bad new IGBT without commutation evidence. |
| Failure happens at no load or light load | CX, C1/C3, C2/C4, transformer primary loop and drive dead time. | Do not assume low current means low switching stress. |
| Turn-off spike or abnormal heating | Snubber/resonant parts, wiring loop, transformer leakage and feedback control. | Do not only increase device rating as a repair. |
| Bridge arms fail asymmetrically | Separate leading-arm and lagging-arm commutation conditions. | Do not compare all four devices as if the arm conditions are identical. |