Circuit
IGBT / MOSFET Induction Heating Power Stage
A WelderData circuit reference for checking industrial induction heating inverter stages without confusing them with arc-welding output circuits.
Database summary
An induction heating power stage usually contains an input rectifier, high-voltage DC bus, IGBT or MOSFET inverter, gate-driver section, resonant tank and work coil. The load is not a welding arc; it is a coupled magnetic load whose impedance changes with coil, workpiece position, frequency and heating state.
For repair, the key is to confirm the DC bus and gate drive before connecting a repaired inverter bridge to the resonant load. A failed tank capacitor, loose coil connection or cooling interlock can destroy new power devices even when the device package itself was replaced correctly.
Power-stage check sequence
- Discharge the DC bus and confirm the machine is safe for resistance testing.
- Check the input bridge, precharge path and bus capacitors for shorts or abnormal leakage.
- Test each IGBT / MOSFET device out of the circuit when possible; do not rely only on online readings.
- Verify gate resistor, discharge path, driver supply and isolation before installing replacements.
- Inspect tank capacitor, work coil terminals and high-current joints for open, loose or overheated connections.
- Restart through a controlled method and watch for protection trip, current rise and abnormal heating.
Failure pattern table
| Symptom | Likely section | Next check |
|---|---|---|
| Breaker trips immediately | Bridge rectifier, DC bus or inverter short | Use power-off diode / resistance checks before applying full mains. |
| Control panel works but no heat | Enable, protection, gate drive or resonant load | Separate command logic from actual inverter output. |
| Weak heating | Tank capacitor, coil coupling, frequency / feedback | Inspect resonant components and load connection before blaming the bridge. |
| Repeated IGBT / MOSFET failure | Driver, tank capacitor, snubber, cooling or overload | Check gate bias and resonant network before installing new devices. |