Circuit
ZX7-250 Overcurrent and Thermal Protection: Current Transformer Feedback and 85C Temperature Switch
A circuit page explaining the ZX7-250 overcurrent and thermal protection paths: current transformer feedback, protection IC input and 85C thermal switch behavior.
Protection architecture
The signal board described in the ZX7-250 notes has overcurrent and temperature protection. It does not appear to rely on a dedicated overvoltage protection function in the explained board. Overcurrent is sensed through a current transformer path, while thermal protection uses an 85C switch that closes when temperature is too high.
Protection diagram
Protection parts
| Part | Role | Diagnostic meaning |
|---|---|---|
| Current transformer / current sensor | senses high current in main path | bad feedback can cause false protection or no protection |
| Protection IC path | receives sensed current signal | covered IC marking may hide exact model, but function remains clear |
| 85C thermal switch | shorts/closes under over-temperature condition | if stuck or disconnected, thermal protection becomes wrong |
| No clear overvoltage path on this board | not a main feature in the explained board | do not assume every signal board has OVP |
Repair meaning
When a welder is stuck in protection, distinguish real overcurrent from false feedback. A shorted power stage should trigger protection, but a bad CT path or thermal input can also block operation when the power stage is not actually overloaded.