I'm using several MOSFETs to control various loads, e.g. pumps, lighting, ventilation etc.
In the implementation, I have several driver circuits on one board (simple emitter follower, which gives good switching speed with a gate voltage of ~5V; using pull-ups were too slow/inefficient), with jumper cables to a board with several MOSFET circuits. Each circuit is like the schematic.
While testing, I touched the signal cable and it caused the MOSFET to turn on, but it got extremely hot in just half a second of on-time.
Now I'm worried that a small failure in the driver circuit, e.g. if MCU is disconnected and the signal wire somehow picks up a small voltage, it will be amplified into the MOSFET gate, causing a meltdown in just a short period of time. Could this start a fire? Or will the device just fail closed?
Ideally the circuit would not even allow the MOSFET to operate in high resistance part of the linear mode. Can I improve my circuit to avoid gate voltages less than, for example, 4V? Is there a way that I can detect/prevent overheating (besides a complicated setup of sensors).
UPDATE: Pull-down on signal Adding a 10k pull-down on the base of the BJTs caused the noise to no longer turn on the MOSFET.
QUESTION: However, it didn't really answer the core of my question, which is more that I'm worried about situations where a MOSFET may turn on ever so slightly, yet able to conduct, causing extreme heat and consequently potentially starting a fire. I can't use a fuse, since the problem is not overcurrent. Perhaps a thermal fuse mounted to the MOSFET, but that seems rather unorthodox. Is this a non-problem that I'm overthinking?