[sdiy] tempco resistors

[Louis van Dompselaar]

That was what I was thinking.  I hadn't seen 3900ppm/K recommended before.

I use the 3300ppm/K ones that were sold on this list by Taku at 40 JPY each.

>> Not quite the 3900ppm/'C that is usually used, but a lot better than 
>> nothing!
> Actually the ideal tempco resistor has a resistance that is 
> proportional to absolute temperature T, as it has to compensate for an 
> effect in the expo pair that is inversely proportional to T.
> This means at 25 degrees centigrade, i.e. 298.15 K, a tempco of 
> 1/(298.15) = 3354 ppm/'C.
>
> Therefore a resistor with 3900ppm/'C is more off than one with 
> 3000ppm/'C by itself. However, you can combine it with a series or 
> parallel resistor to lower the tempco. This easy method of correction 
> is not possible if you have a lower tempco to begin with.
>