Inputs unequal
Fault is upstream in the controller or buffer.
Board · power-device driver
Welder MOSFET / IGBT Driver Boards
Document inputs, returns, supplies and outputs before measuring. Channel-to-channel comparison is safer than applying a generic pinout.
Identify the driver-board function before using a pinout
A welder driver board may use a pulse transformer, discrete push-pull stages, optocouplers or hybrid driver modules. Identify PWM input, driver supplies, isolation boundary, gate outputs and fault signals before assigning connector pins.
Connector inventory
| Group | Possible signals | First evidence |
|---|---|---|
| Control input | PWM A/B, enable, shutdown | Compare both channels at the primary return. |
| Driver supply | Shared or isolated rail per channel | Measure unloaded and loaded stability. |
| Gate output | Gate, emitter/source return, clamp | Label pairs before disconnecting. |
| Fault/protection | FO, desaturation or overcurrent feedback | Confirm polarity and normal inactive state. |
Power-off checks
- Discharge the DC bus and isolated supplies.
- Compare input and output resistance across equivalent channels.
- Check transformer windings, gate resistors and clamp parts.
- Inspect carbonization, cracked solder and connectors.
- Confirm no gate output is shorted to its return.
Low-energy driver test
Power only the driver section. Verify inputs, isolated supplies, fault output and unloaded gate outputs. Use the matching return for each isolated channel.
Compare driver channels
Inputs equal, outputs unequal
Driver device, isolated supply, transformer winding or clamp fault.
Outputs equal unloaded, unequal with gate connected
Gate resistor, power device, connector or emitter return fault.
Fault output active
Separate a real protection event from supply loss or a damaged detection path.
Common driver-board faults
- Open or changed gate resistor.
- Leaky buffer transistor.
- Open pulse-transformer winding.
- Failed clamp capacitor or diode.
- Isolated supply with ripple or collapse.
- Driver module damaged by the previous IGBT short.
- Incorrect emitter-return connection.
Stop conditions
- The return for each output is not documented.
- An isolated driver supply is missing.
- One channel does not match its equivalent branch.
- Fault/protection output remains active.
- Isolation or carbonization damage remains.
Technical sources
- Texas Instruments UC3846 — official current-mode control, current limiting, shutdown, UVLO and dual-output functions.
- onsemi SG3525A datasheet — oscillator, soft-start, shutdown and alternating-output functions.
- Reviewed M57962AL reference set — used for driver supply, input, fault-output and isolation checks; confirm the exact module suffix before using a pin map.
- WelderData ZX7-250 field notes — used for measurement order and branch comparison; raw courseware and board-specific values are not published as universal specifications.
Related repair map
Follow the evidence path from symptom to measurement, circuit and repair case.