Computer Power Supply Overview

One of the largest components in any desktop computer is the power supply. It provides power for all the different hardware in a computer. It is able to provide, in fact, different voltages for different components. They usually have more than one type of connector on them, as well, which is important to figuring out whether or not they are compatible with a given build.

Computer power supplies also provide other elements to the operation of a computer that aren’t necessarily desirable. Just as computer power supplies do the hard work of providing power to the device, they also produce a great deal of heat that builds up in the case and their fans can contribute to the amount of dust that enters the system. They are sophisticated components and they are among the most important choices that builders have to make when they construct a system.

What are computer power supplies?

If you haven’t seen a computer power supply, they’re easy to locate. In the case of a computer, generally on the bottom or top, there will be a rectangular cube. One end of this, the outer side, will hook up to the wall power. The other end will have multiple power outlets hanging off of it. They oftentimes have a separate power switch than the computer itself, usually located on the back of the machine. Most of them have outlet cords that can be detached from the power supply, the cords having a female adapter and the power supply having prongs that plug into it.

The computer power supply functions as a very sophisticated device in its own right. It can take the wall voltage and step it down to several different voltages. Not only do these voltages have to be available, they have to be consistent. This means that the power supply has to provide some protection against unexpected spikes in the power that it distributes to the motherboard and other components.

Computer powers supplies will usually have 3.3v, 5v and 12v connectors on them. They will have various pin configurations on the connectors. These pin configurations prevent the power supply from being plugged into the wrong component by accident. For instance, the power supply outlet for the DVD drive will not fit the power supply receptacle on the motherboard, which prevents potential disasters.

There are adapters available that allow some power supply outlets to be combined or converted into other types where the voltages are compatible. Video cards, for instance, oftentimes have specific types of connectors for power—oftentimes to power separate fans—that may require an adapter to be hooked up to some power supplies to accommodate the device. These adapters make it possible to use power supplies that may have become outdated due to changes in hardware.

Your power supply also has some smart aspects to it. The computer can kill the power to the machine and the power supply is capable of receiving signals from the operating system that tell it to shut down. This is why you don’t have to manually turn the power supply button off when you want to shut down your machine.

When your powers supply is off, it’s not actually off. There are still 5v stored in it. This is how the power supply can receive the on signal from the power button on the computer.

Electrically speaking, power supplies aren’t the most complex devices in the world. Their additional functions, however, greatly increase their overall complexity and make them very convenient to use.

How do power supplies for computers function?

The real heart of a computer power supply is its transformer. These transformers are small, which is why computer cases can be so small. This was not always the way things were, however.

The first computer power supplies were huge by today’s standards. The technology of the time required that these devices used very large transformers to bring down wall voltage to the voltages required by the computers. The computers also used capacitors as part of the circuit that converted the voltage from AC to DC and these were bulky affairs at the time.

The new power supplies use a switching circuit that allows the device to actually take wall current and increase its frequency. This higher frequency current allows the builders to use much smaller transformers, compacting the entire device.

The secondary advantage of this is in preventing variations in the current that could destroy the components attached to the power supply. The higher frequencies are easier to regulate, eliminating some risk.

The switching technology and the better control over the voltages and current it provides make it possible for these devices to safely power very sensitive equipment. Of course, they also have very sophisticated cooling systems attached to them, and that helps to reduce the heat that they contribute to the case on the computer.

The power supply is not done yet. It still has to offer different voltages. There are many different voltages used on a computer and the power supply will have outputs for all of them.

The power supply also has to sit correctly in the case. This is a special consideration, of course, but a power supply that is improperly seated in the case may contribute to heat buildup. In some cases, other components, such as cooling towers on processors, may necessitate that smaller power supplies be used to accommodate the size of some cases.

What is considered Input Voltage?

The input voltage is the voltage that the power supply actually takes into itself. Power supplies do not use the entire wall voltage. They take in the power that they need and no more. This is usually specified on a label on the back of the power supply and will usually have ratings for different types of power systems, such as may be used in different nations.

What is considered Output Voltage?

The output voltage of a power supply is usually multiple. There will be several different voltages listed on the back of the power supply and these correspond to the output of the various connectors that branch off of the power supply.

These connectors determine which components that they can be hooked up to. It’s nearly impossible to hook up the wrong power supply to a component in a computer. Most power supplies come with enough outputs—and adapters can be used, as well—to power the majority of motherboard. For builders, however, it’s imperative to have the right voltages and numbers of connectors on the power supply they use for their build.

What is the Output Current of a computer power supply?

The output current for every power out terminal on a computer power supply is specified on the device. It usually follows an @ symbol: +5v @ 30A, for instance. This is important to selecting the right power supply.

What is the Power Rating?

The power rating is given in watts and determines the maximum power that the computer power supply can offer. This is a vital number in terms of selecting a power supply.

A computer power supply should never be running at 100% of its power rating capacity. How much power it is producing depends upon the number of components attached to it and the power demands of those components.

When the power supply is running at 100% capacity, it produces more heat. That heat can damage the components in the computer or, at least, necessitate that there be more cooling added to the case to offset this. This is why most builders get a power supply that can handle more than the power demands of the build they have in mind. It ensures that the power supply isn’t maxed out during normal operation.

What number of outputs can a computer power supply have?

A power supply can have any number of connectors, but there are 10 main types that are used to power the various components on computers. The computer power supply will likely not have all of them. Many, however, have multiples of the same type, given that some connectors are used on far more components than others. For example, most computer power supplies have one connector for a motherboard and several that will fit DVD drives and other common peripherals.

What mounting types exist?

Panel Mount

Panel mount power supplies are very common and come in various designs. They are generally cube-shaped, with holes or other fastening devices built into them that allow them to be mounted correctly. Most computer power supplies are of this type and are in standardized sizes to make them easy to install.

Rack Mount

Rackmount power supplies are designed to slide into racking systems very easily. They are commonly seen in server rooms and in data centers. They are easily swapped out and replaced, as is everything in a rack system.

Stand Alone

Stand alone power supplies have a case that allows them to be used outside of a mounting system. They are oftentimes seen on the desks of builders, being used to power various types of components. These power supplies include those that are designed to provide power in between the wall current and the device itself, such as UPS systems.

What is considered the efficiency of a computer power supply?

Efficiency is the amount of power that a power supply can generate compared to the amount of power that it needs from an outside source to do so. For instance, a power supply may need 100 W of input to put out 80 W of power, making it 80% efficient. The rest of the energy is wasted as heat, which is important to cooling considerations. For instance, the above power supply would put out 20 watts of power worth of heat into the case into which it was installed, which may necessitate more cooling or which may be handled adequately by the power supply’s native cooling system.

What does MTBF define?

MTBF is a figure that stands for Mean Time Between Failures. This is the amount of time that a power supply can be expected to function without a failure. The numbers for modern power supplies are very high, with some of them having an MTBF that exceeds decade if the power supply runs uninterrupted.

What is the Load Regulation of a computer power supply?

The load regulation defines how much of a variance the power supply can handle in its power source without varying the power it puts out to the components attached to it. This is described in a percentage figure.

What is considered the Line Regulation of a power supply?

This is the ability to keep the output voltage from the power supply consistent when the input voltage varies.

What is the ripple and noise of a power supply?

No electrical systems are ideal. Ripple and noise are variances in the output voltages from the power supply that can be predicted to occur. This is given in the specifications. Modern power supplies are very precise, so this is usually minimal.

What is the length, width and depth of a power supply?

These refer to the physical dimensions of the device. The measurements determine whether or it will fit in a given case.

What is the maximum temperature for a power supply?

This is the highest temperature at which the power supply can be expected to function. Variances in case cooling may present a hazard of overheating power supplies.

What is the minimum temperature of a power supply?

This is the lowest temperature at which the power supply can be expected to perform normally. It’s usually a non-issue unless extreme environments are involved.

What is the weight of a power supply?

This is simply the weight of the entire power supply. It’s important to know because not all mounting systems may be able to handle the largest power supplies. It can determine whether additional means of support need to be installed in a case to support the power supply or whether it needs to be mounted in a bottom position.

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