Inverting Opamp
Here is an example of an operational amplifier. It is in inverting mode
Change the feedback resistor by moving the mouse over the black handle.
Click on it to reset it back to 1000 ohms.
You can vary the input voltage by clicking the green arrow.
Set the feedback resistor to 4000 ohms.
[kml_flashembed movie=”http://www.helpmyphysics.co.uk/opampinv.swf” height=”450″ width=”550″ /]
The gain of an inverting opamp is given by:
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When the feedback resistor is set to 4000 ohms then the gain of the opamp is:
Click the green arrow of the input voltage and note the output voltage.
You can see that the output voltage is always multiplied by -4.
If you increase the input voltage too much the output voltage levels off at -15V.
This is when the amplifier reaches saturation because it cannot give an output voltage larger than the voltage of the supply that works it.
Move the black handle to give the feedback resistor different values and check the gain equation:
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