TABLE OF CONTENTS Most engineers spend a lot of their time trying to get the efficiency up to their expectations. It is often very elusive they improve one loss term, and worsen the other. Or they end up reducing the design/derating margins, thus affecting reliability. Or they cause noticeable deterioration in some other aspect of performance. This is truly one of the most delicate balancing acts in power supply design. As indicated, we certainly can't hope to cover every aspect of this topic here. But we will try to touch on some of the most important points and common pitfalls.
However, before you start, you should have read the previous chapters and therefore actively ruled out PCB design issues, input decoupling issues, and also "junk IC" issues. You should also have asked the Twelve Questions from Figure 8-1 and assured yourself you are not obviously falling into any of the all-too-familiar traps.
The first question you need to ask is, is your efficiency really bad? For example, if you have a worldwide input Flyback of around 70W, you should not be expecting much better than 70% at an input of 90VAC (for the common 5V/12V output rail combinations). For a Synchronous Buck converter, you can expect around 90% at max load, but at very light loads the efficiency will fall much lower. So first assure yourself you really have a problem. And don't forget that this measurement needs Kelvin sensing as described previously (see Chapter 2).
Now, where...
