How do psu rails work

These devices use electromagnetic induction and a set of two coils of wire one having more loops in the coil than the other to step down the voltage; however, transformers only work with an alternating voltage. The more efficient a transformer is, the smaller it can be.

This super fast switching of the DC voltage is the source of the name for this type of device: a switched mode power supply SMPS. You can see 3 transformers in the picture below - the largest generates just the 12 volt output; in other PSUs, the big transformer might make all of the voltages.

The next larger one creates a single 5 volt output that we'll talk about in a bit, and the smallest one acts as an isolator for the PWM circuit, keeping it safe from harm and also stopping it from causing interference with other voltages in the PSU.

It'll all depend on budget constraints and how much power the unit needs to offer. All of them, though, will need to take the output off the transformer and turn it back into DC.

In the image below, the large chunk of metal is the heatsink for the bridge rectifiers that do this conversion. We can also see in this specific PSU, the circuit board in the middle of the picture corresponds to a cluster of voltage regulation modules VRMs that create the 5 and 3.

This variation is called the ripple voltage and for a PSU, you want it to be a small as possible. Cooler Master doesn't provide the size of the ripple voltage in the specifications for this PSU model, so we've turned to a detailed review to find them.

One such analysis was done by JonnyGuru. The image below shows you how this compares to what is required. The quality of the capacitors used throughout the PSU play a significant role.

Smaller, cheaper ones would result in the ripple being bigger, which is not what we want. If it's too big, then the complex electronic circuitry in the rest of the computer might operate in an unstable manner.

Fortunately, in our example, odd millivolts is okay: not great, but not bad. No matter what is used to create the output voltages and ensure they're DC in form, there's still a few more bits of circuitry needed before we start waving cables out the place.

It all relates to managing the PSU's outputs, ensuring that if a high demand for power is taking place on one particular voltage, then the others aren't going to be nobbled in the process. The chip you can see here is called a supervisor and monitors the outputs, checking that they're not delivering too much or too little voltage and current.

It's not very sophisticated, though, as all it does it shut off the PSU, if any of those problems occur. More expensive supply units use digital signal processors DSPs to monitor what's going on, and these can also adjust the voltages if required, as well as send details about the status of the PSU to the computer using it. Not overly useful for the typical PC user, but for computers used as servers, compute machines, and so on, it's often a desired feature.

All power supply units come with long bundles of wires, sprouting out of their back. The number of bundles, and how they're connecting to the main unit will differ across the vast array of models available, but they'll all provide some standard connections. Since voltage is a measure of difference , there needs to be two wires for a given output: one for the indicated voltage e.

This wire is known as the ground or common line, and the two form a loop: running out the PSU, to the device needing the power, and then back into the unit. The flow of current runs through these loop wires, but since some of the loops will only have a small amount of current flowing in them, several ground wires can be shared by different loops.

The first of which is the obligatory pin ATX12V version 2. This is because a computer doesn't really switch off, when you tell the operating system to shut down. The motherboard draws the power it needs to remain active off the standby connection. Graphics cards can only take a maximum of 75W from the motherboard PCI Express slot, so this connector offers additional power for today's monstrous GPUs. This particular PSU actually runs two PCI Express power connectors off the same wires, for cost reasons, so if you had a really powerful graphics card in the computer, it would be best to use a separate bundle of wires.

The difference between the 6 and 8-pin PCI Express connector, is an extra two ground wires. Over the past few years, we've seen an increase number of power supply units proudly wear a tag of 'modular' in their description. All this means is that some of the power connectors are wired to another connector, that slots directly into the PSU. So instead of having a mass of cables and connectors clogging up the inside of the computer case, you can remove what don't need to save some space.

This Cooler Master model, like many others, uses a fairly basic connection system for the modular cables. Well, most people call it a Molex connector , but that's actually the name of the company that developed it. The output supply cabling of a PSU is another area where costs can be saved or given a higher budget, either to improve looks or flexibility of the wires.

The thickness or gauge of the metal wire used in the cables plays a part, too, as thicker wires have less electrical resistance than thinner ones, which results in less heat being generated as current flows through them. At the beginning of this article, we said that most power supply units are named after the maximum amount of power they can offer. At the simplest level, electrical power is simply voltage multiplied by current e.

Like most branded or generic models, our PSU comes with a label providing various snippets of information about how much power each voltage line can provide. And, of course, all of the output voltages come from a single source: the mains outlet.

So the rating of W is the maximum the PSU can provide as a total across all lines. Fortunately, the majority of hardware inside a modern PC takes the bulk of its power off the 12V lines anyway, so it's rarely a problem assuming you've picked the right PSU model for your needs.

Next to the power specifications, there's a label saying " 80 Plus Bronze. The efficiency also depends on what size of load the PSU is attempting to serve i. This would result in the unit drawing to W from the wall outlet. Christopher Jon Mankowski Christopher Jon Mankowski 2, 6 6 gold badges 23 23 silver badges 34 34 bronze badges.

Add a comment. Active Oldest Votes. Rails are independent power channels. Positives: A electrical short on 1 rail will not effect the other rail and vice versa. The same principles apply for 3. Improve this answer. Bon Gart With a W power supply you should not have any trouble. The power supply listed has 8 independent 12 volt channels.

Just remember you can not place more than 20 amps load on any single channel. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. July 11, This is what multiple rails are at their essence, a safety mechanism made to prevent things from melting and or setting things on fire via Over Current Protection monitoring. Well, Most of the time, SCP Short Circuit Protection will kick in before things start melting due to too much current going through a rail.

Power supplies nowadays have so many safety mechanisms that make the debate of single vs multiple rail power supplies fruitless.