[PConline Miscellaneous Talk] Small power supply and big knowledge, unknowingly, the "What You Don't Know" series has arrived in the tenth issue. As the big heart of the PC system, the power supply seems to be as simple as the heart, but it contains a lot of knowledge. In the previous issues, we introduced all aspects of the composition, cost, materials, etc. of the power supply. Today we will continue to talk about the structure of the power supply, which is PFC. Although we can easily know the principles of PFC from encyclopedia articles, this time, we will talk about PFC from a different perspective.
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Power Supply Things You Don't Know (10): Talking about Active and Passive PFC
PFC?
What is PFC? The full name is Power Factor Correction. It translates to "power factor correction". What? These six words are too profound? The editor also thinks so, so let's explain it from a common perspective.
Power factor = active power/apparent power, which is the cos function, and the other side refers to invalid power
What is the power factor? It is a data used to measure the power efficiency of power consumption equipment (including: broad-based power consumption equipment, such as transformers, transmission lines, etc.). The formula for defining power factor: power factor = active power (true power)/apparent power. Active power is power consumed by the device and converted into other energy. Appearing power means what we often call power capacity. 1 Subtract the power factor is the recative power coefficient.
Although the above paragraph has nothing to do with the power supply we use, as a power supply equipment, it still occupies a very important position in the power supply specifications. In this way, it is easy for everyone to understand: the larger the power factor, the higher the power utilization rate.
When we understand the power factor, the definition of power factor correction (PFC) is easy to understand: the technology in order to improve the power factor of electrical equipment is called power factor correction.
Why do we need PFC?
The current and voltage extreme values are different. There will be a phase difference between the current and voltage, which will cause the loss of exchange power
We know that power supply is a capacitance input circuit. Since the maximum current and maximum voltage values of alternating current do not occur at the same time, in this case, a phase difference will occur between the current and the voltage, which will cause a loss of the exchange power. Therefore, the product of the power calculation formula "current*voltage" does not equal the power of the current doing the work. Moreover, the actual power is lower than the power capacity.
I believe everyone knows that the editor does not know how to pretend to understand if he doesn’t understand the PFC circuit diagram. OK, you guessed it right how to avoid this loss of
? At this time, the PFC circuit is required to increase the power factor to reduce the loss of exchange power. What we call PFC generally refers to PFC circuit, and its function is to reduce the loss of switching power.
However, it should be noted here that "power factor" does not equal "conversion efficiency". Now some merchants interpret the active 0.99 power factor as being able to obtain 99% power conversion efficiency, which is obviously wrong, because the power factor refers to all active power, and active power includes not only electricity but also heat. The power conversion efficiency is only for power supply and is not included. What is the use of
PFC? It is to let you taste as much beer as possible in the limited wine glass capacity
Although both describe the concept of power saving, the meaning of the two concepts is different for individuals. Fictionally speaking, a high "power factor" of PFC saves money for the country, because it can waste less power supply and avoid waste of electricity, but electricity to heat cannot be avoided; while a high "conversion efficiency" saves money for users, with low power supply, and does not include other concepts.
Active PFC and passive PFC
Currently, there are two types of PFCs, one is passive PFC (also known as passive PFC) and active PFC (also known as active PFC).
Active PFC
Active PFC is mainly composed of high-frequency inductors, switching tubes, capacitors, and control ICs. It can be simply summarized into a boost switching power supply circuit. The characteristics of this circuit are complex in structure, but have many advantages: the power factor is as high as 0.99, low loss and high reliability, the input voltage can range from 90V to 270V (wide input), etc. Since the output DC voltage ripple is very small, the power supply using active PFC does not need to use a large capacity filter capacitor.
Passive PFC
Passive PFC is usually a large inductor, and its interior is composed of multiple silicon steel sheets wrapped with copper wires outside. Its principle is to use inductance compensation method to increase the power factor by reducing the phase difference between the fundamental current and voltage of the AC input. The power factor of the passive PFC is not very high, and can only reach 0.7~0.8, so its efficiency is relatively low and the heat generation is relatively large. Passive PFC is not useless. It has a simple structure, low cost, and good stability performance, making it more suitable for mid- and low-end power supplies.
PConline Summary of the power supply designed for active PFC on
and the power supply designed for passive PFC on
Nowadays, PFC has become the standard structure of power supply. Although there is a big gap in the status of active PFC and passive PFC, they are essentially not right or wrong. Active PFC is designed with complex, better performance and high cost; passive PFC is designed with simple, low failure rate and cheap price. The relationship between each need and complementary depends on your consumption cost. Nowadays, on JD.com, power supplies that generally adopt passive PFC design basically only appear within the price range of less than 200 yuan, while most of them use active PFCs above 200 yuan. This shows that active PFC is an inevitable trend in the future development of power supplies.
Previous review:
Power supply What you don’t know (9): 80 PLUS how important is? http://diy.pconline.com.cn/769/7697740.html
Power supply What you don’t know (8): Where are the various outputs responsible? http://diy.pconline.com.cn/760/7602401.html
What you don't know about power supply (7): Briefly describe the working principle of power supply http://diy.pconline.com.cn/730/7307700.html
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