Component Ratio/Product Calculator

This script is useful if you need to choose resistors or capacitors in a specific ratio. You specify A/B, 1+A/B (noninverting amplifier gain) or A * B. The script will tell you all possible standard values of A and B, along with the resulting error in the desired quantity. A and B can be resistances, capacitances, or whatever, in whatever units you want. You can find the best resistor or capacitor to use, and if your stockroom is out of that value, you can find the second best!

The error shown is computed using the nominal values of the components; component tolerance is not taken into account.

This script assumes that negative-valued components exist; A is always considered to be positive. (It is possible to construct a circuit that behaves as a negative resistance!)

To enter a non-standard series, choose "Other" and then enter a comma-separated list of values on the interval [100,1000). Here is more information about standard resistor values.

[top] Examples

[top] Example 1: Noninverting amplifier

You want to construct a simple noninverting amplifier, using an op amp, with a gain of 23.1. You want to use 5% tolerance resistors. The gain is given by G = 1 + (R2 / R1), so let B = R2 and A = R1 and enter 23.1 into the "1 + B/A" box. You see that the best choice of component values is A = 68 and B = 1500, which results in an error of -0.18%. A general rule of thumb in op amp circuits is to use resistances in the 1KΩ - 1MΩ range, so R1 = 6.8KΩ and R2 = 150KΩ, with 1 + R2/R1 = 23.06.

The Caltech EE stockroom, as of 2007, sold components in the following values: