Op amp learning

Question

I teach electrical engineering and during 5 weeks, we cover the basics of op-amp. However, I felt that there wasn't enough content since I had a lot of time for review before the exam.

On a theoretical level we cover:

• Derivation of the gain equation for inverting and non inverting op-amp
• Op amp golden rule (try to maintain v+ and v- balanced and no current enter the op-amp input)
• Quick calculation for summing amp and differentiator topology.
• Comparator
• Gain
• Saturation voltage

On a practical level, we do different circuits based on the theory.

My question is: what is the next logical step if I want to push a bit more? My current choices are: GBW, slew rate or simply add another topology. keep in mind that it is an introductory course for technicians and that they mostly do industrial work once out of the school.

If you have any interesting circuits that you had more fun doing within a 2 or 4 hour time frame, I can also look at that. My end goal is to push a bit more and make my labs a bit more interesting.

Answer 1

Before be an engineer, I was also an electronics technician. In a similar way to the course that you teach, the objective of my one was to enable technicians for the industrial segment. Our discipline was about linear and non-linear applications of Op. Amps. For the former case, for example, are the voltage follower, current sources, current amplifiers, voltage regulators and DA converter. A good topic to address are the single supply power configurations (avoiding CMR violation). For the later case (important for the industrial area) are the Schimitt-Trigger, waveform generators - square and triangular, window comparators, etc. A good topic to address is the internal (simplified) model of 555 IC. In the mid are the precision rectifiers.

EDIT

As a practical example of waveform generation with "some" additional glue, consider the high level circuit shown below. This is a way to generate a simple lighting pattern for a water fountain. The figure shows three LEDs (R, G, and B), but my original design drove three 12V high current water-proof incandescent bulbs (one 127Vac/12Vac transformer, three TCA785 ICs and three TRIACs completed the circuit). The complementary E1 and E2 (staircase) inputs are produced by means of 555 oscillator, one R2R network (D/A converter) and two LM324 op. amps. The switches S1 to S6 are implemented with 4066 analog switches. A set of flip-flops and logic gates (mealy machine) generates the signals for 4066's. The challenge was not to use microcontrollers twenty years ago.

Answer 2

I like the classic LM324 VCO circuit. It illustrates the integrator principle and you can make a audio-range VCO with it, which is one of the building blocks of a synthesizer. If you have an amplifier + speaker it's a nice change from the usual blinking LED demos.

Answer 3

^{simulate this circuit – Schematic created using CircuitLab}

A simple portable headphone amp using 9V battery. Input is from a source, example from a cell phone. Output connect to the headphone. Let the 470uF charge to 4.5V before plug in the headphone, otherwise there will be pop sound.