[sdiy] Current source for tempcos in small quantities

[Ian Fritz]

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