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Re: Resistance calculator

by Terry Harris :: Rate this Message:

On Mon, 22 Jun 2009 22:23:58 +1200, Russell McMahon wrote:

>Target R = (Target x existing) / (Target - existing)
>
> RB = (RA x RC) / (RC - RA)
>
>This simple formula is immensely useful when prototyping
>
>eg 87k is required.
>Assume only E12 values at 1% are available.
>
>RA = 100K
>RC= 87K
>
>RB = (100 x 87) / (100 - 87) = 8700/13 = 669k
>680k will probably suffice.

But how or why did you choose 100k for RA?

It happens to be right for 87k and E12s but isn't for say 83k and E12s or
87k and E24s.

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