Circuit path · Feedback / protection / drive
ZX7 / WS feedback, protection and drive path
This page maps the control sequence from current command and feedback through protection shutdown and drive output in ZX7 / WS style inverter welders. It is intended for tracing no-output and false-protection faults without replacing boards blindly.
Control-loop sequence
Current commandFront-panel current pot and maximum-current trim set the requested output.
Feedback inputCurrent transformer, shunt or voltage feedback tells the board what output is actually doing.
Error amplifierControl IC/op-amp compares command and feedback.
Protection logicThermal, over-current, under-voltage or feedback-abnormal path can block drive.
PWM / drive enableDrive leaves the control board only when shutdown is not active.
Driver boardGate-drive transformer/driver stage sends isolated gate signals to power devices.
Measurement points by purpose
| Purpose | What to measure | Meaning |
|---|---|---|
| Command present? | Current-pot wiper and maximum-current trim range. | No command change means front-panel or connector fault. |
| Feedback valid? | Feedback connector continuity and signal response during load. | Open feedback can cause max output, weak output or shutdown depending on design. |
| Protection active? | Thermal switch state, protection lamp node and shutdown input. | Drive may be intentionally blocked even if PWM IC is good. |
| Supply healthy? | 24V and local regulated rails under start and load conditions. | Open-circuit rails can look normal but collapse when relays/drive load the board. |
| Drive leaving board? | Signal at drive connector to driver board. | No signal after protection clear points to control/PWM path; signal present points downstream. |
Typical false-shutdown causes
Open thermal line
Some boards treat an open thermal switch path as over-temperature.
Broken feedback connector
Feedback loss can look like over-current or abnormal output condition.
Auxiliary rail sag
Relays, fans or driver circuits can pull the control rail down during enable.
Signal path principle
When tracing no output, move in order: command, feedback, protection, PWM enable, driver output, gate waveform, then power stage. Skipping directly to IGBT replacement often repeats the failure.