Circuit Simulator Java Applet

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Circuit Simulator is produced by Paul Falstad, and is available from .

Circuit Operation

The output voltage ‘follows’ the input voltage – hence the name of the circuit. The circuit has a high input impedance, so draws very little current from the input, but the output of the op-amp has a low output impedance. The resistor connected to the output acts as a load resistor, drawing current from the output, and is not part of the voltage follower circuit. Please see the voltage follower topic for more details.


  1. Use the switch to connect either the AC alternator, or the DC variable voltage, observing that (a) the output voltage is the same as the input, and (b) no appreciable current flows into the op-amp input terminals.
  2. Measure the voltage on the inverting and non-inverting inputs, confirming that these are the same. Explain this in terms of the open-loop gain of the op-amp. (Clue: this is similar to the virtual earth concept.)
  3. Explain why the input is connected to the non-inverting op-amp input and the feedback link connected to the inverting op-amp input, rather than the other way round. (Clue: negative or positive feedback?)

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