SV: Re: SV: Re: [sdiy] Compensating PTC and NTC resistors

Ian Fritz ijfritz at comcast.net
Tue Mar 18 19:57:04 CET 2008


At 12:15 PM 3/18/2008, René Schmitz wrote:
>Hi Neil and all,
>
>Neil Johnson schrieb:
>>From: karl dalen <dalenkarl at yahoo.se>
>>
>>>So are Elbys calculations right or wrong?!
>>>http://www.elby-designs.com/datasheets/tempco.pdf
>>(minor correction)
>>As Ian said, the *equation* is correct, the *numbers* are a little off.
>
>Correct, but still only of theoretical interest, because you don't really 
>know the *actual* tempco of the series resistor. Could be +50 or -50ppm... 
>If you stick in 0 for TC2 it degrades to the form I have been using. If 
>you stick in the borders, you can use it to assess how large the errors 
>might be.

It sounds like I didn't make the point clearly enough.  The error is in the 
value of the tempco coefficient, which should be 3440, not 3500.  That 
makes a significant error in the series resistor, no matter what *its* 
tempco is.

Ian 





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