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Forum Index : Electronics : Math problem.

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Dinosaur

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Joined: 12/08/2011
Location: Australia
Posts: 323

Posted: 08:48pm 27 Nov 2023

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Hi All

Doesn't seem to matter how I convert the formula in the image, I can't come up with
reasonable resistor sizes.
Allegedly a 0.01uF cap should give 10Khz output with 1mA current.
I assume that is 1mA through R1 & R2.
The Input Voltage is limited to 1.000 V for good linearity.
Again I assumed 1k ohm.
Would love someone to correct me or show me how to calculate the total R with 1V input.

Regards
Hervey Bay Qld.

phil99

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Joined: 11/02/2018
Location: Australia
Posts: 2446

Posted: 09:34pm 27 Nov 2023

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Transposing the equation gives:-

(R1+R2) = Vin / (Fout x Ct x 10)

If Vin = 1, Fout = 10000 and Ct = 10^-8 then (R1+R2) = 1000 ohms.

Same as the datasheet says.

Ignoring all that the op-amp negative feedback ensures the voltage across (R1+R2) is the same as Vin.
R = V / I
1k = 1V / 1mA

Dinosaur

Guru

Joined: 12/08/2011
Location: Australia
Posts: 323

Posted: 10:07pm 27 Nov 2023

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Hi All

Thanks for that Phil.

My error was using uF 0.01 instead of F 0.000 000 010

Regards
Hervey Bay Qld.

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