Overview

When I was writing my first book about designing switching power supplies in 1989, I purposely left this topic till last. Sure, I had taken the control theory classes in college many years before, but they did not relate well to the real-world applications facing me now. So I read all of the papers and books of the day on feedback loop compensation and I was still puzzled. So I took a moment and stepped back and asked myself, "What are they really trying to accomplish?" I formulated the four basic goals of a well-compensated switching power supply. Then I read a paper from Dean Vererable that presented a step-by-step method of determining the location of the compensating poles and zeroes and the resistor and capacitor values fell out at the end. I liked the procedure, but his procedure did not yield the bandwidth I needed for the power supplies. So I borrowed his step-by-step methodology and modified it to fit my purposes.

The following chapter is the result of a lot of work, of which I am very proud. This chapter makes a scary process into a very easy, step-by-step procedure which should only require 15 minutes. It has always worked for me in actual power supply designs.

I start out with a short review of the behavior of elemental circuits in frequency domain using Bode plots. Then we select the compensation method appropriate for your switching power supply topology and control method. We work through the equations...