[time-nuts] Low CostTemperature sensor

Charles Steinmetz csteinmetz at yandex.com
Tue Jan 17 04:17:25 EST 2017

Tom wrote:

> That article has a major error. Anyone know what it is?

Well, the author says the reverse current of a diode is "directly" 
proportional to temperature.  This could suggest that he means the 
relationship is linear (the relationship is actually exponential with 
absolute temperature).  But that's not really an *error* -- just sloppy. 
  "Direct" does not necessarily imply "linear."  An exponential 
relationship is "direct" in the sense that it is what mathematicians 
call "injective" (every temperature corresponds to exactly one value of 
reverse current).

Then, in discussing the LM95235, he says that it can use the 
"collector-emitter junction diode" of a transistor as the sense element. 
  Of course, a bipolar transistor has no collector-emitter junction. 
His diagram correctly shows a diode-connected NPN operating in the 
active region (forward biased, not reverse biased as the rest of his 
article discusses) as the sensor for the LM95235.

Are any of these what you had in mind, or is there more?


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