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DO YOU EXCEL IN ELECTRONICS?

Part 2: The Benefits of Using Excel
by Aubrey Kagan

Start ý Standard Values ý Saving Macros ý Simple Amplifier ý LM317 Calculation ý Goal Seek ý Use of Functions ý Additional Options ý Source and PDF

SIMPLE AMPLIFIER

Figure 1 shows a simple noninverting amplifier. The gain is adjustable by means of a potentiometer. The gain is given by:

where R_eff = R2 + R3. Rewriting this to solve for R_eff,

Because there is one degree of freedom, letýs select R1 = 10K (see Example4.xls (download Excel files)). Assuming you use Method 2 for finding the functions, in order to run this example, NearestValues.xls also must be open.

Figure 1ýHere you can see the noninverting amplifier using an op-amp. The gain may be adjusted by varying R3.

The formula for R_eff is located in cell B8. Letýs assume that the potentiometer is 20% of the total value of R_eff. Aiming for 10% on either side of the ideal R_eff, R1 should be 0.9% of R_eff. This is the formula in cell B10. Similarly, the formula for the potentiometer in cell B12 is 0.2 ý R_eff. Cell B11 looks up the nearest 5% resistor, and B13 looks up the nearest potentiometer. (Actually the nearest potentiometer function doesnýt look for the lower value. It searches for the first value greater than the desired value.) Use one of the two methods to easily insert the resistor value look-up functions when doing this on your own.

To add some versatility to the worksheet, letýs use the standard values to calculate the maximum possible value (R3 = 0) and the minimum value (R3 = maximum). Note that all relevant cells have been named (see Photo 1).

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