Diode - Temperature

[M.Sridhar]

How to measure temperature using diode.Can it be used in such a way?

 

[ed181]

Why would you want to measure temperature using a diode?

 

[ed181]

You can but it looks like a lot of work and it won't be accurate

 

[Old Steve]

@M.Sridhar , did you try Googling this? There is already heaps of info on this subject online. It took me 10 seconds.
And double-posting the same question 25 minutes apart won't get it answered any faster:-

https://www.google.com/search?q=using+diode+to+measure+temperature&ie=utf-8&oe=utf-8

From memory, a diode's forward voltage varies -2mV/degree Celsius.

 

[Arouse1973]

Yes it can. A common method is to use a transistors base emitter diode. Simply pass a constant current through the transistor configured as a transdiode. Have another reference like a potential divider also with a constant current passing through it. Connect this to a comparator and calibrate for use. As the temperature changes the transdiode voltage will change and this can be sensed by the comparator.
Thanks
Adam

 

[Alec_t]

The junction voltage of a diode changes by about -2mV per deg C rise, but if you want to experiment you can use the base-emitter junction of a transistor in an 'amplified-diode' configuration as shown in the attachment, to give a greater change.

This behaves like a diode with a 0.6V junction voltage multiplied by approximately (1 + R1/R2), and a correspondingly multiplied change with temperature.

 

[Arouse1973]

The junction voltage of a diode changes by about -2mV per deg C rise, but if you want to experiment you can use the base-emitter junction of a transistor in an 'amplified-diode' configuration as shown in the attachment, to give a greater change.
View attachment 22308
This behaves like a diode with a 0.6V junction voltage multiplied by approximately (1 + R1/R2), and a correspondingly multiplied change with temperature.

The BE junction of a transistor changes by the same amount. They are all PN junctions.
Thanks

 

[Alec_t]

The BE junction of a transistor changes by the same amount. They are all PN junctions.

Correct. The 'amplified diode' voltage appears between the collector and emitter terminals in the circuit shown.

 

[AnalogKid]

Check with Linear Technology, Maxim, Analog Devices. Somebody out there has a chip that uses a diode as a temperature sensor and turns it into either a thermometer or a thermostat.

ak

 

[Arouse1973]

I put my money on Maxim

 

[Old Steve]

I'd prefer to just use an LM335Z.