# How PN junction diode is used as temperature sensor [closed]

I know the operation of PN junction diode. But I wonder how they use it as a temperature sensor.

• Sorry, but a simple "diode temperature sensor" search turns up a ton of information, if you have a specific question, state the explicit doubt and show what you researched before. Commented Aug 26, 2015 at 10:08
• ..and as you claim "to know the operation of a PN junction" you would be aware of the fact that with a constant current applied, the voltage across a diode or PN junction will decrease by approximately 1 to 2 mV/°C and that it is a fairly linear relationship. As Arsenal suggests do some research. Commented Aug 26, 2015 at 11:24
• Peruse this Commented Aug 26, 2015 at 11:37
• This is a fine question to have in our archive. +1 Commented Aug 26, 2015 at 11:40
• thank u very much for the answers. they were very useful to me :) Commented Aug 27, 2015 at 17:46

Effect of temperature on forward characteristics :

The characteristics curve of a Si diode shifts to the left at the rate of -2.5 mV per degree centigrade change in temperature in forward bias region.

Refer to the graph shown above. The curves are shown far apart just for illustration purpose and are not to scale. The curve shifts to the left at the rate of -2.5 mV per degree centigrade change in temperature. Hence if the temperature increases from room temperature (25° C) to 80° C, the voltage drop across the diode will be (80-25) x 2.5 mV = 137.5 mV.

Note:The values will change with respect to diodes,not all diodes are made up of same parameters and composition.

Hope this helps...

The diode equation is

$I_D=I_0 \left( e^ \left(\frac{V_D}{nV_T} \right) - 1 \right)$

and

$V_T= \frac{kT}{q}$,

so every pn junction has a well defined temperature dependency. Some junctions are optimized for this behavior, but it holds for every junction

• Ok, I know, it's 2018, but you could have added that this behaviour that you refer to only occurs at constant current. Commented Oct 3, 2018 at 14:57