Manufacturing SMPS boards with odd value resistors?

[Faringdon]

Hi,
Customer has sent us some SMPS to bring up.
They are festooned with “weird” value resistors….few are E12 or E24.
They are eg 499k, 249k, 13k7, 2k26, 6k04, 33k6 etc etc...
Surely such resistors are a bad idea, in terms of cost, nil-stock-likeliness, etc etc?

[wraper]

They are OK for feedback voltage dividers. Otherwise it's hard to justify something so specific.

[Faringdon]

Thanks, do you agree they are more likely to be nil-stock than E24?

[TimFox]

Those are popular standard resistance values for 1% tolerance, using the series E96.
1% resistors are often more expensive than 5%, but the difference is less now than in my youth.
They are readily available from the usual vendors.
If 1% tolerance is important to the customer, you also need to see what tempco, etc., he requires.
A handy chart:  https://www.vishay.com/docs/28372/e-series.pdf

[asmi]

These are not weird at all. Nowadays it's not uncommon to see 0.1% resistors in pol dc-dc converters because modern ICs require very precise voltages.

[Faringdon]

Thansk, but this divider is on a PFC output...thats a intermediary rail......only 1% resistors required and E24 is fine.
Also, they have been used on non-divider places.

[TimFox]

If the 1% tolerance is required, then the values will be in the E96 series, which has three significant figures.
The E24 series, used for 5% resistors, has only two significant figures.
General-purpose 1% resistors are manufactured to the E96 series.
If the difference between 499 k and 500.0 k is important to the design (as in a precision voltmeter), then the tolerance will be tighter than 1%.