[sdiy] Current source for tempcos in small quantities

[harrybissell]

I thought the Q81 were 3300 ppm/K ???

In the common use of the tempco (shunting the base of the expo tranny)
will adding the non-tempco in series cause any problems with the value...
or do you just change the series resistor to the base to match ?

H^) harry

Ian Fritz wrote:

> At 02:11 PM 3/9/2003, Jozsef Baksay wrote:
> >At 09:32 AM 3/9/03 -0800, you wrote:
> >>Who's got tempco resistors in small quantities (~10) for a decent price
> >>(like $5 or under)?  My usual source EFM won't have any until he makes a
> >>new order, undetermined at this time.
> >
> >Farnell
> >Manufacturer Code: LT300014T261K0J
> >Order code: 732278
> >3000 ppm, 0.25 W, 1 kOhm, 5%
> >Price: 1.18 £ (pounds)
> >
> >Topy
>
> Hmmm....  The tempco of that one is a bit small.  At 25C the required
> tempco is 3355 ppm/K.  The old Q81 units were pretty good, because they
> were nominally speced at 3500 ppm/K.  You could trim those to the exact
> value by adding a small series non-tempco resistor.  I imagine you could do
> the same thing with the 3900 ppm/K units that Farnell also sells. You would
> need a (nominal) series value of 160 R for a 1k tempco, and twice that for
> a 2k tempco.
>
>    Ian