Snubby is a subsystem of Patchworks that I designed and built to detect overvoltage conditions on supply rails using independent, fully discrete comparator circuits.
The circuit operates in either latching (with hysteresis) or non-latching mode. Red and green LEDs indicate fault status, and a buffered output can drive a load or interface with an MCU or other circuitry.
In my implementation, the output connects to the power-on relay control node, allowing the system to automatically disconnect power if an overvoltage condition is detected. I intentionally added a latching feature so transient events are captured, making it easy to see if a fault occurred while I was away. Ultimately though, When triggered, the circuit disengages the power-on latch and shuts the board down.
Capacitive decoupling and filtering is handled in the main Patchworks project and this circuit is abbreviated as Snubby within it.
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- Tracking versions.
- VCC input triggers at ~12.7 V (12 V + Q1 BE bias).
- 3.3 V rail triggers at ~3.7 V (3 V + Q9 BE bias).
- 5 V rail triggers at ~5.4 V (4.7V + Q5 BE bias).
- Hysteresis provided by R6, R16, and R25.
- Remove these (and the pull-up transistor), or tie them to ground, for non-latching operation.
