Board
SG3525 Control Modules
SG3525 control modules are common in ZX7-style inverter welders and are important for no-PWM, shutdown, soft-start and driver-stage diagnosis.
Board role
SG3525 control modules appear in many inverter welders as the PWM generator for a driver-transistor pair or driver transformer. They often sit between a current-command / feedback amplifier and the MOSFET or IGBT gate-drive stage. A powered board with no PWM may be disabled by external protection even when the SG3525 is healthy.
SG3525 board evidence route
Board-level measurement table
| Board area | Normal / Expected | Abnormal meaning |
|---|---|---|
| Input supply to module | Stable rail at the module connector | Auxiliary supply, harness, regulator or board short fault |
| SG3525 5.1V reference | Stable reference not loaded down | IC fault or shorted external load on reference path |
| RT / CT oscillator | Timing ramp / oscillator activity present | Timing capacitor/resistor, sync/discharge path or SG3525 fault |
| Soft-start node | Ramps up after enable | Soft-start capacitor, diode clamp or shutdown transistor holding start low |
| Shutdown path | Inactive during run command | Protection, VRD, thermal, overcurrent, optocoupler or feedback path is active |
| A/B outputs | Balanced push-pull PWM | Output loading, IC damage or downstream driver short |
| Driver transistor / transformer input | Waveform follows SG3525 outputs | Small transistor, transformer primary, gate branch or load fault |
Repair direction
- Do not replace the SG3525 before confirming supply, reference, oscillator, soft-start and shutdown state.
- If A/B outputs are present but gate-drive transformer output is absent, the driver stage is the next section, not the PWM IC.
- If shutdown is active, trace the protection source instead of bypassing it permanently.
- If one output side is heavily loaded, isolate the downstream driver transistor or transformer primary before condemning the IC.