Chip
UC3843 / KA3843
Auxiliary power supply PWM chip family used in many inverter welder long-strip boards.
Welder-specific function
UC3843 / KA3843 is described here by its role inside welding-machine boards, not by repeating a generic datasheet. In inverter welders, ordinary PWM chips, op-amps and optocouplers are combined with current feedback, protection, thermal signals, VRD logic, driver transformers and power-stage enable circuits.
How to think about chip diagnosis
Supply voltage present
↓
Reference / bias stable
↓
Command and feedback pins reasonable
↓
Shutdown / protection inactive
↓
Output waveform present
↓
Driver stage responds
Practical checks
| Check | Normal / Expected | Abnormal Meaning |
|---|---|---|
| VCC | Stable within application range | Startup or auxiliary supply fault |
| Reference | Stable reference voltage | Chip supply or IC failure |
| Feedback / command | Changes with current setting | Open pot, feedback fault or protection path |
| Shutdown / protect | Not latched active in normal operation | Protection, VRD, optocoupler or transistor fault |
| Output | PWM or logic waveform present | Chip disabled, damaged or blocked |
Repair note
Do not replace the IC only because the machine has no output. Many welder chip faults are caused by peripheral components: startup resistors, small electrolytic capacitors, optocouplers, zeners, current-sense resistors, driver transistors or protection inputs.