Simple and easy-to-understand diagrams of how power supplies work

Definition and classification of power supply

Students, today we are going to learn a lesson about the working principle of power supply. Because it is a knowledge popularization class for novices, I will try to make this class popular, simple and easy to understand with plain language. If there are professional masters passing by, I hope to communicate with you more.

Let's first talk about what a power supply is. As the name suggests, it is a device that provides electrical energy . When we talk about DC power supplies, we mainly refer to two types of power supplies: linear power supplies and switching power supplies .

Power supply classification

Next, let's compare the differences between these two types of power supplies, as shown in the figure below.

From the table above, we can conclude that high-frequency switching power supplies are more suitable for our computer power supply devices. The most common power supplies on the market also use a closed-loop system, which is responsible for controlling the circuit of the switch tube, obtaining feedback signals from the output of the power supply, and then increasing or decreasing the frequency of the voltage within a certain cycle according to the power consumption of the PC so as to adapt to the transformer of the power supply (this method is called PWM , Pulse Width Modulation). This improves the effective utilization of electrical energy and reduces the loss of electrical components .

In the current market, this type of high-frequency switching power supply using a closed-loop system can be divided into two types according to its structure: power supplies with active PFC design and power supplies with passive PFC design.

Because the production cost of the power supply with active PFC design is higher than that of the power supply with passive PFC design, we can simply think that the power supply with active PFC design is a relatively high-end power supply, while the power supply with passive PFC design is a relatively low-end power supply.

Mains to computer DC power

Next, let's talk about how this high-frequency switching power supply is used in our lives. As we all know, the electricity we use in our daily lives is 220V AC, while our computers need DC. So, how does this switching power supply achieve such an energy conversion? Let's use a few pictures to explain this conversion process.

From the diagram above, we know that the direct current of the computer is converted four times by the power supply.

The mains power passes through EMI → low voltage AC passes through the rectifier bridge → the pulsating voltage passes through the capacitor → the rippled DC passes through the transformer and the secondary side → low voltage DC is obtained.

The four transformations are:

1. The mains electricity is converted into low-voltage AC power through EMI;

2. Low voltage AC is converted into pulsating voltage through a rectifier bridge;

3. The pulsating voltage is converted into rippled DC through the capacitor;

4. Ripple DC is converted into pure low-voltage DC through a transformer and filter circuit.

Now we know the simple process of converting AC power into low-voltage DC power for computers. Next, let's explain this process in detail.

The structure and function of the four parts

From the previous diagram, we know that the mains power is transformed through four parts and five times to finally get the low-voltage direct current of the computer. Now let's explain which four parts of the power supply complete this transformation. First, let's take a look at the current flow chart.

Current flow diagram

Next, we will talk in detail about the role of the above four parts in the process of converting AC power into computer DC power.

1.220V AC current enters EMI (transient filter circuit), first enters primary EMI (consisting of capacitors and ferrite inductors ) and then enters secondary EMI (consisting of MOV varistor, ferrite coil and fuse), and filters out high frequency and pulse interference in the current through "X" capacitor (metallized polyester capacitor), and flows out AC current without spikes and low voltage;

2. The low-voltage AC current enters the rectifier circuit, enters the rectifier bridge (which can be composed of 4 diodes or a single component), is corrected and rectified, and flows out a unidirectional pulsating DC voltage, i.e., a pulsating voltage;

3. The pulsating voltage flows into the main capacitor part, flows through the polyester capacitor and ceramic capacitor to filter out high frequency and pulse interference, flows through the main capacitor to filter and prevent interference, and flows out DC with voltage fluctuations, i.e. ripple DC;

4. The rippled DC current enters the transformer and the secondary side. It first enters the transformer for voltage stabilization, then enters the secondary side, where it is stabilized and rectified by the voltage regulator IC chip, voltage regulator diode and high- power Schottky rectifier bridge on the secondary side. The polyester capacitor performs filtering here, and finally obtains pure low-voltage DC power, which is the computer DC power.

After the above explanation, we can roughly understand the simple principle and process of the switching power supply to convert AC power into DC power for computers. In order to facilitate everyone to build a complete knowledge framework, I use a knowledge structure diagram of power supply here to help everyone understand and remember the knowledge content of this series of articles.

Through the above structure diagram of power system knowledge, I believe that everyone has established a simple system framework of power knowledge. I wonder if you have obtained enough effective information? If you think it is too theoretical and impractical, you can read my article on practical purchase skills. If you want to trace the source and further understand the relevant knowledge, you can read my related theoretical articles. Finally, please look forward to our next class.