The power supply unit is one of the most important parts of your CPU. It basically converts the AC power supplied by your house mains into DC power. As only DC power can be used by most electronic components of the PC, such as RAM, CPU, hard drive, disc drives, and video cards.

But what goes inside a power supply unit? How does a PC PSU work? This article will explain the working mechanism and construction of a PC power supply unit in detail.

Let’s get started!

What is a Power Supply Unit?

In simpler terms, a power supply unit is nothing but a voltage rectifier. The rectifier straightens the sine waveform of the alternating current into a direct current. Let’s first understand why there is a need to convert AC power to DC.

Almost all electronic circuits run on direct current. This is because these circuits operate using binary inputs of 0 and 1. Since the alternating current changes its polarity multiple times during a single cycle, it doesn’t go well with the binary operation. You would get multiple on and offs with AC. This is where a power supply unit comes in.

I’ve simplified the concept of a power supply unit by calling it a voltage rectifier. In reality, there is much more to it. In the next section, we will discover the main parts of a PSU.

What are the Main Parts of a PSU?

Before we dwell into the working of a power supply unit, let’s familiarize ourselves with its construction and major components. Here they are:

  • Main input
  • Electromagnetic interference remover
  • Power Adjusting Transistors
  • Transformer
  • Transient filters
  • Capacitors
  • Cooling fan
  • Outputs

In the working section, we will look at the detailed function of each of these components.

How Does a PC PSU Work?

Although there are multiple types of power supply units, the most common of all is the switch-mode PSU. Linear PSUs are a thing of the past, but we’ll briefly discuss those as well to have some necessary background information.

Linear PSU

There are four main components of a linear power supply unit. It comprises transformers, diodes, capacitors, and regulators. The main AC input is applied to the transformer. Since the voltage supply in most countries ranges from 208-240 Volts, a transformer steps it down to the required DC voltage.

DC voltage is usually in the range of 3-12 Volts. This huge difference between AC and DC voltage makes the use of a transformer a necessity. Then this stepped-down voltage goes to a half-bridge or full-bridge rectifier circuit. A half-bridge rectifier uses two diodes, and a full-bridge uses four.

The difference between the two is evident from the name. A half-bridge rectifier only straightens the upper half of AC waves. In contrast, the full-bridge rectifier straightens both the upper and lower halves of AC waves, hence a more superior inversion from AC to DC.

For those of you who don’t understand bridge rectifiers, it is important to note that their output isn’t 100% DC or straight. It still needs some treatment. So, the output is passed through a series of filters and capacitors to further increase the efficiency. In the end, there is a regulator to adjust the DC voltage.

Switch-Mode PSU

Now let’s discuss the working of a modern and more widely used type of power supply unit, the switch-mode PSU. The working theory of a switch-mode PSU is the same as that of a linear PSU; just a few more electronic circuits are added. But you get a lot of benefits from adding these.

First of all, the size of a switch-mode PSU is much smaller as compared to the linear PSU. The reason is that the operating frequency of a linear PSU is the same as that of mains (50-60 Hz). However, in the case of a switch mode PSU, this frequency is increased up to 50,000-1,000,000 Hz.

As there is an inverse relationship between the size of electronic components and frequency, naturally, smaller capacitors, transformers, and inductors are used in the switch-mode PSU. Hence, the lesser weight means a lighter final product, and it is cheaper as well.

The working of a switch-mode PSU starts with an electromagnetic interference remover. Here, the unwanted waves are filtered out, and only AC power makes its way to the next step. During this step, the AC power is converted to DC as it is done in a linear PSU.

From here, the difference begins. When high-power transistors are used to convert DC power back into AC but at a very high frequency. Since it is much easier to amplify a DC wave as compared to direct inversion plus amplification of AC power.

Then a transformer steps down the voltage of these high-frequency AC waves. After that, the final AC to DC inversion takes place, and the output is passed through the series of filters. That’s pretty much how a PC PSU Works.

Final Words; How Does a PC PSU Work?

It is evident from the name of the power supply unit that it supplies power for PC operation. If a PSU goes bad, you won’t be able to turn on your PC. It is the backbone and powerhouse of your computer.

In this article, we discussed the functions, construction, and working of a power supply unit. We hope that it clears any misconceptions or queries you have regarding a PSU.

Have you ever opened the PSU of your computer? What wires and components did you notice? Do let us know in the comment section down below.