1. Op Amps Intro to ECSE Analysis K. A. Connor Mobile Studio Project
Center for Mobile Hands-On STEM
SMART LIGHTING Engineering Research Center
ECSE Department
Rensselaer Polytechnic Institute
Intro to ECSE Analysis

2. Outline What is an Op-Amp? No Negative Feedback Negative Feedback
Golden Rules
Op-Amp Model
Inverting Amp
Non-Inverting Amp

3. Op Amp – No Feedback
An op-amp produces an output potential (relative to circuit ground) that is typically hundreds of thousands of times larger than the potential difference between its input terminals. Open loop gain is very, very large. Output is limited by power supply voltages.

4. Op-Amp Negative Feedback
If predictable operation is desired, negative feedback is used, by applying a portion of the output voltage to the inverting input.

5. Golden Rules of Op Amps If there is negative feedback
In a closed loop the output attempts to do whatever is necessary to make the voltage difference between the inputs zero.
The two inputs draw no current

6. Op-Amp Model
A more realistic model of the op amp when the inputs draw a very small amount of current and there is a small output resistance.

7. LTspice Analysis
Feedback, input & load resistors and source.

8. LTspice Analysis
Vin vs Vout
Transfer Function?

9. Inverting Op Amp
V+ = V- = 0
Current in Rin = Current in Rf

10. Non-Inverting Op Amp V+ = V- = Vin Current in Rin = Current in Rf
See also Voltage Divider Videos

11. Special Case
Why do this?

12. Many More Possibilities
Negative impedance convertor
Also:
Integrator
Differentiator
Differential Amp
Instrumentation Amp …