Feedback Control

Abstract

This chapter uses insight to explain how to control and stabilize switched-inductor power supplies. It shows how inverting feedback loops mix, sample, and translate signals across the loop, how they respond across frequency, and how pre-amplifiers, parallel paths, and embedded loops alter their response. The material also discusses how power-supply systems use operational amplifiers (op amps) and operational transconductance amplifiers (OTAs) to stabilize feedback systems. With this understanding and insight in hand, the chapter explains how analog and digital, voltage- and current-mode, voltage and current controllers manage and stabilize switched inductors in continuous and discontinuous conduction. Along the way, it introduces and reviews phase and gain margins, gain–bandwidth product, unity-gain projections, Types I–III dominant-pole, pole–zero, and pole–zero–zero stabilization strategies, non-inverting and inverting feedback and mixed op-amp translations, inherent stability, digital gain and bandwidth, limit cycling, and other relevant concepts that help describe, quantify, and assess feedback controllers. Illustrative figures, equations, examples, and SPICE simulations complement discussions throughout.