Resistor with very low Temperature Coefficient.

[mchambin]

What is available at affordable cost ( say < $10 ) with lowest TC.
Tolerance does not matter.
I would love a servey at costs
<$1 <$2 <$5 <$10

 

[trobbins]

I recommend Metrology - Page 1

 

[mchambin]

I found the answer.
Very simple:
Available at Mouser.
5ppm/K is affordable from $1.
2ppm/K is not. Over $30.

 

[454Casull]

Typically you'd look for thin film resistors.

 

[trobbins]

The metrology section has sage advise on actually achieving low TC with such resistors - it's a different world.

 

[mchambin]

Interested, but I don't find it.

 

[jcarr]

The temperature coefficient is one piece of the puzzle, but it should be combined with an awareness of how the temperature of the resistor will be altered by the power that it will dissipate in a given application.

For resistors that will experience large voltage swings (NFB resistor for example), the voltage coefficient should also be considered.

 

[mchambin]

Of course, self heating and thermal resistance to ambient matter, as well as layout.
I need low TC and low Rth.
So far Vishay PTF 1/8 watt seems the way to go.
Any better ?

 

[cbdb]

The larger the power rating the lower the temp changes. Use larger resistors.

 

[wlowes]

Caddock USF

I have had very good results with Caddock Type USF 300 Series Ultra-Stable Resistors for feedback resistor. Partsconnexion used to carry them at around $8 ea.
http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeUSF.pdf
You'd have to search for a source.

 

[jcarr]

The larger the power rating the lower the temp changes. Use larger resistors.

Agreed. 10ppm in a 0.25W part and 10ppm in a 2W part mean different things.

An alternative is to use lower-value resistors in series, which will take care of the voltage coefficient and temperature coefficient in one operation.

 

[jan.didden]

Indeed. Instead of a feedback resistor of 20k feeding 1k to ground, use 21 identical 1k resistors and assuming iso-temperature, the temperature and voltage coefficient effects nicely cancel.

Jan

 

[EUVL]

Practical with SMD.


Patrick

 

[mchambin]

Indeed. Instead of a feedback resistor of 20k feeding 1k to ground, use 21 identical 1k resistors and assuming iso-temperature, the temperature and voltage coefficient effects nicely cancel.

Jan

Yes, assuming all resistors from a same batch have same TC, which is not guaranteed.
May be more likely, with SMD.

 

[mchambin]

Indeed. Instead of a feedback resistor of 20k feeding 1k to ground, use 21 identical 1k resistors and assuming iso-temperature, the temperature and voltage coefficient effects nicely cancel.

Jan

Made from resistor arrays ?
Are they arrays such that they have near same TC and near same temperatures ( as done in ICs ) ?
Or, all resistor arrays, just resistors put together.
Arrays I need: up to 9 same value resistors.
To make
R, 5R
R, 5R
R, 8R
R, 7R

 

[mchambin]

I found Vishay NOMCA 8 independant R
TC absolute +- 25ppm
TC tracking +- 5ppm
With four of these, I will implement
Gain +8 OAP non inverting with R, 7R
Gain -1 OAP inverting with 4R,4R
SY to ASY Gain 0.2 OAP with 5R,R and 5R,R

 

[Vovk Z]

You can parallel resistors in smaller divider leg and get more dividing coefficients.
For example 4R and R//R (four series and two in parallel) gives 8 and so on.
6R and R/2 is 12.

 

[MarcelvdG]

Indeed, but then the self-heating is not the same anymore for each unit resistor.