I agree with both of you. I can't imagine using the reverse leakage of a
diode to measure temperature without some difficult and expensive design.
Also, the transistor is using the forward biased B-E diode against what he
stated in the article.
And sloppy would be the best description.
Thanks guys. Glad I am not the only one forming that opinion.
Regards,
Tom
----- Original Message -----
From: "Scott Stobbe" <[email protected]>
To: "Discussion of precise time and frequency measurement"
<[email protected]>
Sent: Tuesday, January 17, 2017 9:10 AM
Subject: Re: [time-nuts] Low CostTemperature sensor
Thermometry based on Diode leakage current wouldn't be impossible I
suppose, you might loose some hair in the process.
The signal levels on the opamp are goofed too.
On Tue, Jan 17, 2017 at 4:19 AM Charles Steinmetz <[email protected]>
wrote:
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?
Charles
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