possible tempco with KTY81

Rene Schmitz uzs159 at uni-bonn.de
Wed Nov 17 02:51:12 CET 1999


At 01:11 17.11.99 +0100, prophet5 wrote:

>If we assume a linear relationship beetween 273 and 323 degrees Kelwin :

It is not exactly linear. But I think it doesn't matter. Consider that
wirewounds with tempcos ranging from 3000ppm to 3900ppm are sucessfully
used for compensation. That 
little mismatch which would occur above and below the chosen reference
temperature 
(for which the compensation would become exact) will be smaller than the
error you make using a 3000ppm type versus the 3300ppm required. (In a fair
temperature range arround room temperature. 20-40°C)

...
>Now we can assume : 
>
>R1 = 2K2 (set the Op.Amp gain to 1 circa)
>R3 = 1K
>
>This jelds R4 = 59.87 R3 ==> R4 = 56K + 10Ktrimmer
>
>Is all correct or i'we misunderstanding something ?

Yes, but you have some more freedom. You don't have to make the opamp unity
gain, you can choose the gain lower to use 100k input impedance. Then you
can change the R3/R4 divider accordingly. You'd end up with a scheme
similar to my VCO3. Or one can as well use the KTY in the divider after the
opamp.

Bye
 René



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