Controller Circuit

Previous: Practical Matters.

This circuit is the basis of a temperature controller. Study it and then answer the questions that follow. The questions have links to outline answers but please resist the temptation to look at these until you have written down your own answers to all the questions.

1. What does the circuit do, and how does it work?
2. What additional circuit is needed between the output and the heater?
3. Why is there a diode in series with the output?
4. Why might one want to make R2 much larger than R1?
5. What is the purpose of R3?
6. What might be the most serious effect of op-amp offset voltages and bias currents?
7. How might the impact of op-amp offset and bias be reduced?
8. How would you consider improving the circuit?