Entering a value for Gain will find the optimum values for R1 and R2. If you specify the values for R1 and R2, the gain is found. If you enter a resistor values (R1 or R2) along with the gain, the other value will be found.
The circuit configuration shown is a non-inverting amplifier. It take the input voltage and provides an amplified version of it at the output. When the input is positive the output will be positive and AC waveforms appear in phase between the input and output. Unlike the inverting amplifier, the non-inverting amplifier can not have a gain of less than 1.
The use of R3 is optional and can be removed (R3 is replaced with a conductor). It is used to reduce the offset voltage error of the op-amp. A full discussion is given in “Op-amp Errors (Article)”.
The input resistance of the amplifier is essentially an open circuit (typically tens or hundreds of gigaOhms for modern FET input devices). This is due to the arrangement of the feedback loop where the input is connected directly to the op-amp with no other connections present at that node in the circuit.
The output resistance of the amplifier will appear to be 0Ω as long as the current rating of the op-amp is not exceeded by the load current in combination with the current through R2.
If you don’t like the magnitude of the resistor values found, you can divide or multiply the values by a multiple of ten and the resultant values will still be a standard value.
This solver uses the following equation to compute its values.