Why does your computer need a power supply anyway? You've already got tons of power coming right out of the wall. It blew the fuse. 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 Sea sonic. 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 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 Electro BOOM 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 chucka 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 hour 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 - 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. 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 pace 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.
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 in2020 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.
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.
0 Comments
Post a Comment