The objective of this article is to provide detailed information about the most crucial part of a personal computer (PC) system, its power supply unit. Follow us on this journey into PSU territory and we promise that you will gain valuable knowledge.
For those of you who know nothing about PSUs, today we're taking it from the top. The abbreviation PSU stands for power supply unit, and in this article, we assume that it is also an SMPS (switching mode power supply), since in modern PCs only SMPS units are used.
You can think of the PSU as the heart of a PC; it is the most significant part of the system since it feeds power to the other components, including the CPU, graphics card, hard drive, SSD and so on. If the PSU fails, it affects all of the other pieces. And in some cases, a malfunction of the PSU can damage other components as well, especially if the PSU is of low quality with inefficient protection features. Unfortunately, this is something many builders ignore. Instead of choosing an adequate PSU for their systems, users typically acquire all of the other components first, using leftover funds for the power supply purchase. If you've made this mistake, we are sure that after reading this article you will change your PC building strategy. However, this article is not just intended for novice users and goes beyond the basics of PSUs, providing valuable information to experienced enthusiasts as well.
In the following sections we will provide an easy-to-follow explanation of the switch power conversion. We will also make a brief reference to the most significant electronic components currently used not only in PSU manufacturing, but also in every modern electronics device. Through the following pages you will learn the basic concepts of inductors, capacitors, resistors, transistors and diodes in order to better understand PSU components. Next, the main context of switching power conversion will be explained and a brief description of the various stages that compose a PSU will be made. Afterward, we will make a brief reference to some switching regulator topologies, which are commonly used nowadays. Some of you might not be aware of this, but a PSU's cooling fan is usually the first part to stop working, at least in good-quality PSUs, so we will dedicate some time to discussing cooling fans as well. Next, we'll spend some time on protection features, and finally we will take a look at ATX, EPS and 80 PLUS specifications.
This is going to be an informative journey through electronics, and when you finish reading this article, we are confident that you will have gained valuable knowledge that will help you to better understand the "Look Inside" pages in our
PSU reviews. In addition, you will be able to judge the technical specifications of a PSU by yourself.
In the following section, we briefly describe the most significant electronic parts that are used in PSUs, including inductors, transformers, capacitors, resistors, transistors and diodes. This essential knowledge will help you when we analyze the internal parts of an SMPS, especially if you don't have an electronics background.
Inductors
An inductor, or induction coil, stores electrical energy in a magnetic field. Inductors are used in many electronics and they play an especially important role in PSUs. An inductor is simply a coil of wire wrapped around a core (composed of iron, ferrite or simply air). Depending on their usage they have several names: coils, chokes, solenoids, etc.
So how do inductors work? The whole concept is very simple: when a current passes through an inductor, a magnetic field is created around the wire. Every change in current affects the magnetic field, which in turn induces voltage across the inductor. That voltage creates a current flow opposite of the initial current. This property is known as inductance (L) and it's measured in henries, which is a quite large unit of measure usually documented in millihenries (mH) or microhenries (μH).
Here are some interesting facts about inductors:
- They store electrical energy in magnetic fields.
- They act as an open circuit at first when DC (direct current) is applied to them, but after a while they freely allow it to pass.
- They oppose current changes.
Transformers
Now, let us take a quick look at transformers. Typically, inductors are shielded so their magnetic fields do not interact with other components in the same circuit. However, if we place two unshielded inductors side-by-side and feed one of them with AC (alternating current), then its magnetic field induces a voltage not only in the current inductor, but also in the other inductor. The process of inducing voltage in the second inductor is called mutual inductance. So if you pass current in one inductor you create voltage in the inductor near it.
A transformer is nothing more than two inductors, or coils, wound around the same core material in a way that mutual inductance is at a maximum level. The coil that lets the current pass is called a primary coil and the coil that is induced with voltage is called a secondary coil. A transformer can electrically isolate two circuits and also step voltages up or down.
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