What you will learn in this chapter
- Verify closed-loop regulation under load change (mirrors Ch3 Lesson 1)
- Verify closed-loop regulation under VIN change (mirrors Ch3 Lesson 2)
- Understand proportional feedback improvements and limitations
Chapter 4 of 5 · Chapter Overview
Closed-Loop Feedback: Making Buck Auto-Regulate
Build a complete feedback loop with voltage divider + error amplifier + comparator + sawtooth to auto-adjust D against load and input changes.
The previous chapter showed three open-loop problems: output rises with light load, drifts with VIN changes, no auto-correction. This chapter uses a real closed-loop circuit (divider sensing + comparator + sawtooth = auto PWM) to address each problem, and discusses proportional feedback limitations.
How to use this chapter
Each demo in this chapter directly mirrors the corresponding Ch3 scenario. Same conditions, closed-loop circuit gives output much closer to target.
Mirrors Ch3: Light Load — How Closed-Loop Responds
In Ch3, R=100Ω caused open-loop output to rise to 8.2V. Under same conditions, closed-loop output≈6.3V — error reduced from +37% to +4%.
2Mirrors Ch3: VIN Step — How Closed-Loop Responds
In Ch3, VIN stepping from 12V to 15V caused open-loop output to rise to 7.5V. Under same conditions, closed-loop output only rises to ≈6.1V — error reduced from +25% to +2%.
3Monte Carlo: Closed-Loop vs Open-Loop Output Distribution
Compare closed-loop vs open-loop output distribution under random load variation using Monte Carlo simulation to verify feedback's robustness improvement.