Overview

The control section is important for the behavior of the switching power supply. It has a direct effect on output regulation, transient response, efficiency, and its reaction to adverse operating conditions. There are several methods of controlling a switching power supply, each enhancing certain aspects of the operation, but also possibly creating difficulties in another area. The selection of the best control method for your particular application should be based upon a good understanding of each of the needed operations.

The feedback loop compensation (Chapter 9) is the last aspect of the design of the control section. The type of compensation used will determine the stability of the supply, the accuracy and the transient response of the output.

Even after designing the perfect control section, other unseen factors can affect its proper operation. I once modified a supply design I had used before. I gave my schematic to the printed circuit board designer and later built the prototype. I simply could not get the supply to regulate and it oscillated badly. I then examined the PCB layout. It was electrically correct, but the control was on one side of a noisy ground node and the voltage sensing circuit was on the other side. Lots of noise was being injected into the sensitive input of the error amplifier. I then had to instruct the PCB layout person on the techniques of good layout practices. The next prototype operated flawlessly. In short, ignorant PCB layout designers and autoroute are...