How to Use a Standard Rectifier Diode as a Thermal Cutoff Switch

In this video, Jon Gabay demonstrates how to use a standard rectifier diode, such as a 1N4004, as a thermal limit switch. This can be a useful improvised solution when a thermal cutoff sensor fails, for example on a space mission's maneuvering thrusters.

He'll explain how the reverse-biased diode exhibits a small leakage current that is proportional to temperature. By monitoring this reverse current through a resistor, we can build a simple op-amp comparator circuit to detect when the temperature exceeds a set threshold.

The video walks through the circuit design, showing how to adjust the trip point using a trimmer pot, and demonstrates the thermal switch in action by heating the diode with a soldering iron. This low-cost, DIY thermal limit switch could be a valuable technique in situations where off-the-shelf sensors are unavailable or unreliable.