Technical Bulletin – January 2019

The Case of the Missing Energy An Overview of AC/DC Conversion Losses


What constitutes an ideal system? This is vague question that is sure to yield a multitude of different responses depending on who you ask. If you ask a power electronics engineer, they will probably tell you that an ideal system is one without losses. Unfortunately, in the world of power electronics there is no such thing a system without losses. Basic physics tells us that amount of energy in a closed system is a fixed constant. What then is a closed system, and why in all cases do we get a little bit less out of a power supply than we put into it? Efficiency is a commonly referenced power supply specification, and one that receives a lot of legislative attention. Efficiency ratings range widely from product to product, but you wont find a power supply rated for 100% efficiency.

This months technical bulletin provides a high-level overview of the loss mechanisms in a modern day AC/DC power converter. Note that a number of loss mechanisms will be discussed, many of which could quite easily warrant a full technical bulletin independently. It is not the purpose of this article to thoroughly detail the physical or mathematical subtleties of each mechanism, but rather to shed light on just where all that missing energy is going, and why. Read more (view pdf) >>

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