How can I make a diode heat sensor?

[sv_clintrace999]

Hi everyone!

de DV9HRV of the Philippines. I just want to ask if there is any way to make a fan heat sensor other than a thermostat? perhaps a diode sensor, I mean i want my fan to turn on if it detects heat for about 35c-40c.

Thanks

 

[dougy83]

If you provide a constant current through the diode, the voltage across it is proportional (negative slope) to the temperature. If you want to derive this yourself, you can use the Schockley equation https://en.wikipedia.org/wiki/Diode

Alternately, instead of the constant current source, you can use a resistor connected to a power supply. This will cause the voltage / temperature relationship to be nonlinear, but this is fine for your application.

You'll need to calibrate your voltage threshold of the diode at the threshold temperature

 

[alec_t]

To use a diode as the sensor means you will need to amplify small voltage changes (~ few mV) to a useful level. Quite doable (my previous house had diode sensors for a home-brew central-heating controller), but you might find a cheap typical NTC thermistor easier to work with as its resistance changes significantly with temperature.

I think if I lived in a country with temperatures of 35-40°C my fan would be permanently on and not need a sensor .

 

[MikeMl]

**broken link removed**

Reference 2

found using Google with search terms: diode used as temperature sensor