1. The Inverting Mode Op-Amp

2. What is the Inverting Mode ? The op-amp can be connected up in various ways or modes. What it does depends on how it is connected up. When connected up in the inverting mode, it changes positive voltages to negative voltages. It may also make them larger.

3. The Inverting Mode Op-Amp + - V1V1 VoVo RfRf R1R1 0 V +V s -V s The feedback resistor ( R f ) is used to control the gain of the op-amp. The input voltage is fed in through the input resistor ( R 1 ).

4. Revision – The Gain of an Amplifier You may remember from Standard Grade that the gain of an amplifier is the ratio of the output and input voltages. The gain can also be expressed in terms of the resistors used to connect up the op-amp.

5. The Inverting Mode Gain Equation

6. Example 1 + - 15 mV VoVo 200kΩ 10 kΩ 0 V +V s -V s Calculate the output voltage from the op-amp below.

7. Example 1 - Solution

8. Example 2 + - 15 mV -6 V RfRf 10 kΩ 0 V +V s -V s What size of feedback resistor would be required to produce an output voltage of – 6 volts ?

9. Example 2 - Solution