Which resistors should I use to generate a gain of 15 on an inverting amplifier?

[qablos]

I have the set of values for resistors available:
10-12-15-18-22-27-33-39-47-56-68-82

And I need to get a gain of 15, which values should I use to get this?

Also, I have a non-inverting amplifier, and again, I need a gain of 15. I selected the values:
R₂=12 and R₁= 68+82+18=168
I assumed I was able to combine some resistors in series to solve this problem...

Is this correct?

 

[NascentOxygen]

Hi qablos. There are lots of "inverting amplifier" circuits, should we assume you are using an op-amp with just 2 resistors?

You list the resistor values available, as 10-12-15-18-22-27-33-39-47-56-68-82. Are you sure those are all you have? Are they all just Ohms? If so, they are not suitable, resistors of just a few Ohms are too low for most op-amps.

HOWEVER, I think it is probably intended you should understand that the resistances available to you are those values x10ⁿ where n is any integer 0..12 or so.

So you have 10Ω, also 100Ω, and 1000Ω, and 10kΩ, and 100kΩ, and 1MΩ, and 10MΩ, etc. Also, 12Ω, and 120Ω, and 1200Ω, and so on ...

 

[skeptic2]

Quablos, why not use R2 = 10 and R1 = 68 and 82 in series?

 

[CWatters]

Oops someone beat me to it.

 

[rezeew]

To generate a gain of 15 on an inverting amplifier, you will need to use two resistors in a specific ratio. The gain of an inverting amplifier is equal to the ratio of the feedback resistor (Rf) to the input resistor (Rin). In this case, to achieve a gain of 15, you will need to use a Rf value of 150kΩ and a Rin value of 10kΩ, based on the available resistor values provided. This will result in a gain of 15 (150kΩ/10kΩ = 15).

For the non-inverting amplifier, you will need to use the same ratio of resistors to achieve a gain of 15. However, in this case, you can use multiple resistors in series to achieve the desired values. Your calculation for R1 is correct, as it is equivalent to a 168kΩ resistor. However, for R2, you will need to use a combination of resistors in series to achieve a value of 12kΩ. One possible combination is 10kΩ + 2kΩ, which will result in a total value of 12kΩ.

In summary, to achieve a gain of 15 on both an inverting and non-inverting amplifier, you will need to use specific ratios of resistors. For an inverting amplifier, the ratio is Rf/Rin = 15, and for a non-inverting amplifier, the ratio is (R1+R2)/R2 = 15. Using the available resistor values, you can achieve these ratios by combining resistors in series.