How a Power Supply Works and Why It’s so Important

Many times we have talked about the power supply as the heart of the computer, how important it is that these are good quality. But have you ever wondered exactly how a computer’s power supply works? And, why is it so important that it does its job well? In this article we will explain in detail (Note: this article is technical and extensive, and is for those who like me are curious about the inner workings of things).

Power Supply

First of all, I have to say that in this article I’ll try to use vocabulary and terms that everyone understands, because although it may be easy for a person who has studied electronics, it may be very difficult for someone who isn’t as technical. I will try to speak in a balance of technical and comprehensible lingo, but keep in mind that we are talking about electronics after all and that, therefore, technical terms of this matter must inevitably be introduced. That said, let’s go.

How Power Supplies Work

The most essential function of a PC power supply is to convert AC (Alternating Current) to DC (Direct Current). Old power supplies converted alternating current into multiple DC voltages (+ 12V, + 5V, + 3.3V) simultaneously. In contrast, modern power supplies convert all AC power into + 12VDC, and once converted, other DC-DC converters convert the + 12V + + and + 3.3V, everything that our equipment needs. This last technique is more efficient because the voltages that are less used (the + 5V and + 3.3V) and are not converted if they are not needed, in fact converting from DC to DC is much more efficient than from AC to DC since it requires less electronic components that are smaller in size.

Power Supply

Once we have the voltage (remember that the voltage is the electric voltage, while the amperage is the intensity, not to confuse the terms) converted to direct current, it is filtered through inductors and capacitors. This is where two parameters come into play: voltage regulation, to ensure that it is stable, and electrical noise, because a higher noise results in more damage caused in the components as a result of heat. Let’s explain this.

Electrical noise and how it is filtered

PC power supplies use a switching technology to convert AC power to DC. Whether the rectifier is on or off, DC pulses are generated at a rate set by the AC input, which in the case of Spain is 50 Hz (this is important because this depends on the country, in Mexico it’s 60 Hz for example). This is called noise.

First, the voltage goes through an inductor (or choke), which softens the shape of the electric wave and reduces the frequency of the noise. Then the capacitors come into play, which as you know are essential for the power supply. The capacitors store the electric charge and are able to “release” it without the noise that we’ve spoken about. This is the way to do it is because if the voltage entering a capacitor raises or lowers the switching frequency, the capacitor load goes up or down but much slower than the switching frequency, causing the previous noise to dissipate in the form heat and the voltage comes out clean.

With this we have eliminated the noise waves that are created (ripples), or in other words, small peaks and valleys in the output DC voltage. This is where large capacitors or a series of capacitors come into play, because the slower the change between the lowest and the highest voltage, the more stable the output will be and this ripple effect will be reduced considerably. However, care must be taken in designing the power supply in this respect because if there are too many capacitors, or the capacitors (or inductors) are too large, we would be reducing the efficiency of the power supply. Each and every part of an electrical circuit has a bit of energy loss in the form of heat, and in the case of capacitors, the dissipating heat is precisely the noise, but in the end it’s lost power. A balance must be sought.

In the oscilloscope report you can see the ripple measurement on a power supply that does not have a good line-in filtering.

Power Supply

When the power supply does have a good line filter, it should look like this on an oscilloscope:

Power Supply

Voltage regulation, an essential factor

Let’s move on to the second factor we talked about at the beginning, the voltage regulation. In general terms it is basically how well or poorly the power supply responds to changes in load (consumption). Let’s say that the power supply is delivering us + 12VDC to 2A of intensity, and suddenly we run a game and the load goes up to 10 amps, or even to 15 amps. This is where Ohm’s law comes into play, which surely many of you have studied in physics or even mathematics in school.

According to Ohm’s Law, the more the current increases the more the resistance increases, and the more the resistance increases the higher the voltage rises at the same time (the resistance is the only value that remains unaltered). A good quality power supply must be able to compensate for all this, usually through internal monitoring performed by a component called “supervisor IC”, which is able to tell the PWM (Pulse Width Modulation) controller what it is necessary for the rectifier to switch to at a different frequency in order to adjust the output voltage accordingly. The most modern power supplies are digital, and this process is done by digital monitoring, making this compensation run much faster.

If this voltage regulation is not done quickly, the internal components suffer much wear and tear in the form of heat (lost energy), which also leads to a decrease in efficiency.

Although we have talked about three DC voltage values (+ 12V, + 5V and + 3.3V), a computer actually needs many more different values in order to work. The DDR4 RAM runs at 1.20-1.35V, and there are many different possible values at which a processor or graphics card works. It is the voltage regulator that is in charge of supplying the value that each component needs at any given moment; For example, in the case of RAM, the controller converts the value of + 3.3V into the 1.35V that you need.

Why it is essential to have a good power supply

If it hasn’t become apparent to you yet let me explain more simply: a good power supply that is capable of delivering a stable and noise-free power will not only make you spend less money on electricity (which is very expensive), but will also help all of your components (motherboard, processor, RAM, graphics card, hard drives … everything is connected to the power supply and therefore we always say it is the heart of a PC) to have a longer life expectancy by heating up less and working more efficiently.

If we add to this that the power supply is what has all the necessary protections (over and under voltage, over and under current, short circuit, etc.), we sincerely hope that the next time you have to buy a power supply for your PC, you don’t skimp and go for a good quality.

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