- Why does your computer need a power supply anyway?
You've already got tons of power
coming right out of the wall.
(cool music)
It blew the fuse.
(laughing)
That's why.
But why didn't this work?
And what does the power supply actually do?
To answer those questions
we'll be taking you through all the stages
of your computer's power supply
and how they work sponsored by Seasonic.
From the wall
you get alternating current or AC power,
which historically has been cheaper to generate
and efficiently transport over long distances.
Which is great, but not for a computer.
Computers work by storing ones and zeros in logic gates
and for logic gates to function
a very stable input voltage is required.
AC which goes from positive to negative voltage.
Many times a second could be used,
but it's kind of like how you could also build a car
with square wheels.
You shouldn't.
So then our wall AC power needs to be converted
to direct current or DC, which has a constant voltage.
No problem.
Let's talk about linear power supplies.
From the wall you're getting either 110
or 220 volt AC power.
Since we're in North America
we'll be using 110 volt for our examples.
Now that is still a way higher voltage
than what you want for your computer.
So the first major stage is a transformer
that takes us from 110 volt AC
to 12 volt AC.
Transformers are relatively simple.
When AC current travels through a wire
it creates a magnetic field.
This magnetic fields can be made much stronger
by wrapping the wire into a tight coil.
And then if you place another coil right beside it
the changing magnetic field will start moving the electrons
in the second wire.
That voltage that you get on the second wire
is then determined by the number of turns in each coil.
So to take our 110 volts down to 11 volt
we could have a hundred turns on the primary side
and just 10 on the secondary.
Once we're at a more manageable voltage
we're ready to turn that AC into DC using a rectifier.
Rectifiers work on the basis that diodes
only allow electricity to flow in one direction.
So you chuck AC through it
and it spits something a little bit like this.
You just add a capacitor and bam DC.
Now the formal name for this circuit right here
is single diode rectifier,
but more commonly in electrical engineering circles.
You'll hear it referred to as crap.
That's where something called a
full bridge rectifier comes in.
For a more detailed look at the full bridge rectifier.
You can check out this classic from ElectroBOOM
but we can get you through the basics.
By using four diodes in this configuration
on the positive wave
electricity flows through diode one and three
to complete the circuit.
And then on the negative wave
it goes through diodes two and four.
That leads to much less waste.
Then from here, you just chuck a capacitor on the output
and boom, you're good to go.
Linear power supplies are actually still used
for many things, including musical instruments
thanks to their ability to deliver very clean power.
But unfortunately you wouldn't want to use one
for your computer
due to their 60 Plus Turd efficiency rating.
And then there's also the fact that they
only work for a single input frequency and voltage.
So power supply manufacturers would have to make
completely different models
of the same power supply capacity
for every different market.
So wait a second.
Why did I just explain linear power supplies then?
- Because someone had to give them the background
that they need for this next part
about what we actually use.
Switching-mode power supplies.
Let's take a journey through your PSU
starting at where the AC enters and leaving,
where the DC goes to your motherboard.
Before we can even worry about converting from AC to DC.
We need to do a bit of filtering.
So these little blue boys in here
they're called Y-capacitors
and the gray one right there.
That's an X-capacitor.
These guys preventing your computer
from sending electrical noise back into your house wiring.
Which could cause problems with other devices.
Meanwhile, we also have to filter the incoming power.
So your computer doesn't get all screwy
when your roommate fires up the blender
to make some margaritas.
My favorite part of this EMI filtering stage
is hidden in here.
It's called a metal-oxide varistor or MOV.
And it's cool because this changes it's resistance
based on the input voltage.
So normally it's just chilling there
acting as an open circuit,
but when a voltage spike comes in
it's resistance drops and that extra energy
just gets chucked to the ground instead of,
blowing up everything else.
In cheap power supplies the MOV might be omitted.
And if it is, you should omit that power supply
from your parts list.
Once the signal is clean
we can turn our attention to power factor correction.
As AC flows through inductors or capacitors.
The voltage and current
will get out of phase with each other
resulting in wasted energy.
This bank of MOSFETs and big ol' inductor,
make sure that you get as much
from your AC input as possible,
at which point is chucked through a rectifier right there.
And out of that, you get three to 400 volts of DC.
Next, these Big Chungus capacitors
smooth out the voltage of the DC current
flowing from the main bridge rectifier.
And side note
I would strongly recommend not licking these.
Now let's talk about the most surprising part
we've from AC which comes from the wall
to DC which your computer needs.
And now we're going to go back to AC
and stay with me here because the payoff is huge.
To do it we run DC through our MOSFETs that are
right there giving us AC power
but in a square wave, which is fine
except that every time that a MOSFET gets turned on or off
you lose some efficiency.
To almost entirely reduce these switching losses.
A technique called soft switching is used.
So in parallel to these MOSFETs is a capacitor
and an inductor that will begin to resonate
as the MOSFETs are switched.
The resonator creates a sine wave.
And by syncing up the MOSFET switching
to when the sine wave is close to at zero
you can almost entirely eliminate the switching losses.
I'm not even going to pretend how to understand the math
behind how this works.
But, if you think you've got the stuff
here's a paper to enjoy as part of your PhD
in electrical engineering.
Long story short, we now have AC power again
but it's perfectly power factor corrected
and at a much higher voltage and frequency
compared to what's coming out of your wall.
This allows the main transformer rate here
to be both much smaller, and a lot more power efficient
as it converts into 12 volts AC
which is then fed into the rectifier right there.
And you have 12 volts DC for your PC.
For those of you paying very close attention.
That was it.
We finally came back around
to how your computer uses a linear power supply
but not quite like we talked about before
just with extra steps.
- Hey, there it is.
I knew we were gonna make it back here.
Then, we take that 12 volt DC
and we add some hefty capacitors for filtering
and to improve transient response.
In layman's terms, this 3,300 microfarad capacitor here
is gonna do a lot to prevent a voltage drop.
If your RTX 3090 decides it suddenly needs 500 or 600 Watts
for a few milliseconds.
Not everything in your PC uses 12 volt however,
so we also need these DC-to-DC buck converters
to get us 3.3 and five volts,
giving us everything we need to run a computer,
except the ability to turn it on.
See this other mini transformer over here.
This little fellow takes our high voltage DC from before
and turns it into five volts standby,
which is always on even when the computer is turned off.
Allowing it to power things like motherboard RGB,
and always on USB charging ports.
And also it powers the power button so that you can
fire up your machine and get on with important tasks.
Like visiting lttstore.com, where we have great merchandise
like these high quality t-shirts,
fantastic water bottles, and even...
- But none of that really explained why good power supplies
can cost anywhere from one to $500.
Something you've probably heard talked about
in community forums and even power supply marketing,
is component quality.
With Japanese capacitors coming up a lot.
But do they even make a difference?
These days, probably not.
But that doesn't they're a bad thing.
Between 1999 and 2007 there was a capacitor plague
where a capacitor is made in Taiwan experienced a
higher than expected failure rate
due to issues with the raw materials
used to manufacture them.
While capacitors in Japan experienced no such problems.
Since then Capacitors made in China and Taiwan
have greatly increased in quality.
And the vast majority of Japanese capacitors
are just Japanese branded capacitors.
They're actually manufactured in China.
With that being said
there are still some value to vet Japanese capacitors
because typically they're designed
and tested to meet the quality requirements
laid out by the Japanese companies
overseeing their production.
To figure out if any individual company is good though.
Tom's Hardware created a capacitor tier list
that you can reference when trying to figure out
if a specific component is good or not.
The overall capacitance of your power supply
can be a double-edged sword though.
One thing people often get wrong
is automatically assuming high efficiency
equals high quality
but not unfortunately, this isn't always true.
An easy way to boost the efficiency
of your power supply is to reduce the capacitance.
You no longer have to worry about
charging up those big old caps so you waste less power.
But you could fire up a game
and end up rendering nothing but a black screen.
- And do we have hardware info.
And that my friends
is why you don't buy your power supply on Aliexpress.com
- Evaluating how different power supply manufacturers
have balanced efficiency and transient response
is beyond the scope of this video.
But we wanted you to know that filtering by 80 plus rating
and sorting by price, isn't the way to go.
Low capacitance can also be a problem
for small form factor power supplies.
There's simply less space to add capacitors.
In general this won't be a problem,
but if you're building an SFF PC that is high powered
maybe consider over specking the power supply a bit
just to be on the safe side.
Also to be on the safe side
never mix modular cables
between two different power supplies.
Even if they look identical.
There's a chance they are different.
And if they are it's magic smoke time.
It's always bothered me why they aren't standardized though.
And I was finally able to ask.
It turns out the answer is pretty simple.
Everyone developed modular power supplies
around the same time
and the connectors were almost arbitrarily chosen
by the each company based on their current PCB layout
and the connectors easily available from their suppliers.
Maybe modular cables can get standardized
if the specs change.
And there is a good chance the spec for power supplies
could change soon.
The ATX Standard has only gotten relatively small revisions
since it was created by Intel way back in 1995.
And there are some problems with this,
like power supplies in 2020 needing to output
3.3 and five volts.
Despite these voltages barely being used by modern hardware.
But this could be changing soon in June, 2020 version 2.53
of the ATX Standard was added
where the power supply would only be delivering 12 volts.
And the motherboard would be responsible
for DC-to-DC conversion.
As I showed in this video,
this should result in significant
real-world efficiency improvements especially at idle.
But the people we talked to
wished Intel had gone even further
and switched to 24 or 48 volts.
Like you might find in applications.
Basically, higher voltage means less current
at a given power,
and less current means less heat generated
and a higher efficiency.
Which brings us to the final reason
why buying a quality power supply is a good idea.
Good old mother earth.
As much as electronics makers try and put a positive spin
on their environmental progress, Apple.
Pretty much every component in your PC
will offer up mediocre performance in a few years
or be downright broken.
High quality power supplies though
can last you through multiple upgrades.
Seasonic the sponsor of this video
has up to freaking 12 year warranties
on some of their units.
So at least that's one part that won't end up
in a landfill anytime soon.
So huge thanks to Seasonic for sponsoring this video,
providing us with technical support for this piece,
and thanks again to Johnny Guru for his insight as well.
Thanks for watching this video.
And if you were looking for another (indistinct)
I can't do it.
And if you're looking for another Turbo Nerd video
maybe check out how motherboards work
Turbo nerd.
Turbo nerd is so hard to say fast.
You chucked it twice in the same sentence Alex,
killing me.
I'm done I'm out.