Original subtitles

In this lesson,

we're going to talk about input and output voltages.

Now, I've touched on input voltages

a couple of times already,

but it's really important to understand.

When you're looking at the world,

it's divided into multiple different types of power,

depending on where you live and where you're working.

For example, here in the United States, where I live,

we use what's known as 120 volts AC, or low-line power.

Now this is actually a misnomer

because it's not always going to be 120 volts AC

when it comes out of your wall outlet.

Sometimes it can be as low as 110

and sometimes it can be as high as 125.

But if you're having good, clean power,

it should be 120 volts AC.

And that is what your power supply is expecting

if you're living here in the United States

and you have a U.S.-based power supply.

Now, in other parts of the world,

you may find that you have 230 volts AC,

or what is referred to as high-line power.

This is what's used in Europe and Asia

and some other places like that.

Now, I've had students in the past who ask me,

why do we use different standards here in the United States

versus Europe versus Africa versus the Middle East

versus Asia or Latin America?

Well, the reason is that,

over time, as electricity was first invented,

it was actually being invented in multiple different places

using multiple different types of systems.

And so, depending on what part of the world you grew up in

and how electricity was brought to your part of the world,

that's going to help determine what kind of electrical power

you have in your country.

Now, regardless of which one you have,

it doesn't really matter 'cause you can use both of them

as long as you have devices that support that power type.

For example, I personally have lived

not just in the United States,

but also in Japan, the Middle East, and in Europe.

And in each of those places,

I could take my computer with me and still use it.

And I could do that safely.

The way I did this is because I was able to set the voltage

for my power supply.

And most power supplies will support multi-voltage

by being able to select which one you're going to use.

On older power supply units,

there's actually a little switch on the back.

And you would select 115 or 230,

depending on which side of the world you lived on.

Now, in modern power supplies,

a lot of these are what are known as voltage sensing

or dual voltage power supplies.

With these newer power supplies,

you can plug it into either of those outlets,

whether it's 120 volts AC or 230 volts AC.

And it will detect that and then work with that power

as the source and convert it into the voltage of DC

that you need for your computer,

regardless of what that input is.

But here is why we're talking about this.

If you plug in a single voltage power supply

that only supports one of these

into the wrong type of outlet,

you can have a lot of bad things happen.

For example, if I took my U.S. computer,

using 120-volt power supply

and plug it into a 230-volt AC outlet in Italy,

it will actually break my power supply

or even possibly catch fire.

This was actually a problem

with some of the first Xbox consoles.

For example, I had several friends who were in the military

and when they took their Xboxes with them

overseas to Europe and they plugged in

their 120-volt AC power supply from that Xbox

into their 230-volt AC outlet in their house,

it actually broke their Xbox

and caused that power supply to fail

and smoke and was no longer usable.

So it's important to understand what the voltage is

that you're going to be using

and what your power supply is set to.

Now, you may be wondering,

what happens if you do it the other way?

What if I buy a device in Europe

and I try to plug it in over in America?

So I'm taking a 230-volt device

and plugging it into a 120-volt outlet.

Will that damage the device?

Well, no.

But the computer or the other device will simply not turn on

because it's expecting 230 volts

and you're only giving it 120 volts.

So it doesn't have enough power to do its job.

And this is why it's important to understand

what your device supports and what kind of power you have

in the area you're working.

Now, in addition to that, it's not just based on

where you're working in the world,

because we do have some 230-volt devices

here in the United States, as well.

For example, in my home, I have a dryer

that I use to dry my clothes.

That is actually a 240-volt AC device

and it uses a 240-volt plug that goes into my wall outlet.

If I plug my computer into that outlet,

that might cause some problems

if I have it set to 120-volts AC.

So you need to keep this in mind

when you consider input voltages into your power supply.

What is the source that is going to be provided

to that power supply?

Is it 120 volts or is it 230 volts?

Now, in addition to that,

our power supply is going to take that input voltage

and it's going to use its transformer to convert that down

to a lower voltage, down to about 12 volts.

Then it's going to pass it through filters and rectifiers

to be able to create the three voltage levels

that we need to use

for our various components in our system.

These are 3.3 volts, five volts, and 12 volts.

And all of these are DC or Direct Current.

Now, I want you to remember these three voltages

because they're really important

and test writers love to ask questions about this.

So remember, 3.3 volts DC, five volts DC,

and 12 volts DC.

Once your power supply creates these three voltages,

it's going to send that out over

the different connectors we talked about,

like your main board or motherboard power cable,

your CPU or processor power cable,

your PCI express power cables,

your SATA power cables, and your Molex power cables.

Now, when you look at these,

we actually are going to get DC,

and DC is either positive or negative.

And in our system, we're going to use both positive

and negative 12 volts DC as part of our system.

Then we're going to use positive 3.3 and positive five

for those other low voltages that we need.

Now, when we talk about these different voltages,

you may hear people use the term rail.

Now, a rail is simply a wire

that provides current at a particular voltage.

So you may have a cable or wire

that is providing 12 volts DC.

That is a 12 volt DC rail.

That is the way people refer to this

when they talk about power distribution within a computer.

Now, when it comes to these three voltages

of 3.3 volts DC, five volts DC, and 12 volts DC,

the most important of these is the 12 volts DC.

For most modern computers,

the rating of the plus 12 volts DC rail is probably

the most important factor

when you're measuring and determining

what power supply to use.

This is because this is the most commonly used voltage

in the PC, by the motherboard and other components

that require a high amount of power.