Can I know which component senses heat or acts as heat sensor in the following circuit? In the given diagram, it is said that the 1N4148 diode acts as the sensor. But basically it is a zener diode and I don’t think that it is able to sense temperature shift. This circuit provides a working model but the sensor remains as a mystery for me. Can you please help it for me?
Here is the datesheet of 1N4148
Any diode can be used as a temperature sensor.
You put a small forward current through the diode and measure the voltage across it, it will change about 2mV for each degree Celsius.
will it be linear, or require any special fomular?
Linearity will be fairly good, but you have to keep the current very constant and you have to calibrate the range (2mV is not a precise value).
i see, using LM35 is more simple then
To use standalone yes.
In some situations a diode (Can be the BE diode in a transistor) will be cheaper. I believe that chips with build in temperature sensors often use a diode.
See
https://www.google.com/search?q=diode+temperature+coefficient&ie=utf-8&oe=utf-8
for more info (equations, graphs, etc.
It’s fairly linear over a decent-enough range, just don’t try it for cryo or high-temp environments.
Here’s a simple circuit that adjusts offset (zero-adjust) and gain (sensitivity):
Go crazy…