It is no mystery that semiconductor junctions modify their habits with temperature, and you can use this reality to make a temperature sensor. The dilemma is that you have to calibrate every product for any specific transistor you want to use as a sensor, even if they have the identical aspect quantity. Back again in 2011, the famous [Jim Williams] mentioned that even though the voltage wasn’t identified, the variation involving two readings at different existing amounts would keep track of with temperature in a known way. He exploited this in an software be aware and, lately, [Stephen Woodward] employed the very same theory in an oscillator that can go through the temperature.
The circuit utilizes an integrator and a comparator. A FET switches involving two values of collector present-day. A comparator drives the FET and also serves as the output. Somewhat than test to puzzle out the circuit just from the schematic, you can very easily simulate it with LT Spice or Falstad. The Falstad simulator does not have a way to transform the temperature, but you can see it operating. The design is not great sufficient to actually read through a temperature, but you can see how the oscillation operates
You can feel of this as a temperature-to-frequency converter. It would be quick to read with, say, a microcontroller and change the interval to temperature. Every single 10 microseconds is equal to a degree Kelvin. Not terrible for a little something you do not have to calibrate.
Thermistors are a further way to evaluate temperature. Occasionally, you really don’t have to have a sensor at all.
