# take me to a world that has 90k resistors

Discussion in 'General Electronics Chat' started by badbaud, Jun 11, 2011.

Mar 5, 2009
26
0
I have tried all of the major distributors for a 90k 1/4w 1% resistor and no one has responded. Metal film or foil or wirewound, I don't care.

Does anyone know of a source for these resistors, I need 100 right away for a project.

Apr 5, 2008
15,801
2,386
Hello,

Take two 180K resistors parallel.

Bertus

3. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
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Or take 22kΩ+68kΩ in series. They would need to be 0.5% tolerance to meet the 1% tolerance requirement. Ditto for the parallel case as well.

4. ### strantor AAC Fanatic!

Oct 3, 2010
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Dec 26, 2010
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I don't see the need for two 0.5% resistors to get a 1% tolerance combination. Combining resistors of a given tolerance in series or parallel gives a result of the same tolerance worst-case. In fact, the statistical distribution of the combined result tends to be tighter, as to obtain a worst-case result requires two devices to be at their tolerance limit.

It is true that the worst-case percentage tolerance error given by a large ratio potential divider can approach double that of the resistors it is made from. That can be relevant if you are making something like an attenuator.

6. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
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Yes Adjuster - I see my error. Thanks.

7. ### #12 Expert

Nov 30, 2010
16,685
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293-9.1m-rc
9.1 meg, 5%
9 cents at Mouser.
90.9k//9.1M = 90.001k

8. ### Tang New Member

Jun 11, 2011
2
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if the resister is used for DCDC's feedback, you can change the both resistence same time.

Apr 30, 2011
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90.9k is the standard value for 1%. Strantor's Vishay 0.1% at Mouser for \$0.38 is probably it for you.

10. ### wmodavis Well-Known Member

Oct 23, 2010
737
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It is a good thing for designer and/or hobbyist to be aware of and take into consideration 'standard' values for components to save from having to undergo your type of frustration. What if there were no standard values that could be manufactured and readily available. And of course as has been pointed out in the above responses, it is also a good thing to be familiar with the myriad of ways to get intermediate values when it imperative to have one. And IMO a third good thing is to know how to recognize whether it is in fact imperative or not.

11. ### tom66 Senior Member

May 9, 2009
2,613
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Not necessarily true. Read this thread. Combined resistors of 0.1% tolerance can give up to 0.2% error worst case!

Apr 30, 2011
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An older technician I knew told me that they used to file away part of the element on large carbon composition resistors to adjust them up in value.

13. ### PatM Active Member

Dec 31, 2010
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Up in value, but down in wattage rating.
Pat - W9ZO

Dec 26, 2010
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Yes, but that is precisely the division ratio error issue that I referred to in the second part of my post. You can indeed get a divider ratio error percentage approaching the sum of the two resistance tolerance percentage errors, but that is not the same situation as building a single composite resistance.

15. ### strantor AAC Fanatic!

Oct 3, 2010
4,302
1,989
Ok, I don't see how you can add the 2 percentages. practical example:
I want a 600Ω resistor ±1% but all I have are (2) 1.2KΩ ±1%
So, 600 + 1% (worst case) = 606Ω
and, 1,200Ω +1% (worst case) = 1212Ω
I parallel the (2) 1212Ω resistors and I get 606Ω - That's still 1%.

Actually I would think that you would have a better chance of hitting your mark by parallelling resistors because, unless both are at the max tolerance, one should pull the other closer to the correct value.

EDIT, ok I see that you are talking about 2 different resistance value. never mind

16. ### #12 Expert

Nov 30, 2010
16,685
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By the way, The principle of the 9.1 meg resistor in parallel is that it is about 100 times the needed value, so its 5% tolerance could only affect the final product by .05%

17. ### ErnieM AAC Fanatic!

Apr 24, 2011
7,436
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From the land of thick film hybrids when designing resistors, which are trimmed to value by cutting into them there is no factor for the kerf.

18. ### PackratKing Well-Known Member

Jul 13, 2008
850
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I have a bad habit ?? of putting an X fixed resistor parallel across an X trimmer pot, and dialing in what I actually need.

It might look a little odd and cobbled, though it certainly works. Nailing the tolerance needed can be tricky, since the little trimmers are none too tight.

It helps to have a shoebox full of trimmers..............

19. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
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We should be asking Badbaud why he needs a 90k resistor. There is frequently another solution if the big picture is seen.