What Is Power Factor Correction?

The full name of PFC in English is "Power Factor Correction", which means "power factor correction". Power factor refers to the relationship between effective power and total power consumption (apparent power), which is the effective power divided by the total power consumption. The ratio of the amount (apparent power). Basically, the power factor can measure the degree to which electricity is effectively used. When the value of the power factor is larger, it means that the power utilization rate is higher.

Chinese name: Power factor corrector
Foreign name: Power Factor Correction

Abbreviation: PFC
Function: Increase the power correction factor of the power supply

Definition of Power Factor Corrector

Basic overview of power factor corrector

Computer switching power supply is a capacitor input type circuit. The phase difference between current and voltage will cause the loss of exchange power. At this time, PFC circuit is required to improve the power factor.

Basic introduction of power factor corrector

In order to improve the power correction factor of the power supply, the country forced the power supply manufacturers to install PFC circuits for the power supply to improve the conversion efficiency of the power supply. In fact, this has also been forcibly stipulated in Intel's power supply design specifications.

There are two types of PFC circuits: active (active) PFC and passive (passive) PFC.

Power Factor Corrector Passive

Power Factor Corrector Overview

Generally, the inductance compensation method is used to reduce the phase difference between the fundamental wave current and voltage of the AC input to improve the power factor. Passive PFC includes silent passive PFC and non-silent passive PFC. The power factor of passive PFC can only reach 0.7 0.8, which is generally near the high-voltage filter capacitor. The structure of the passive PFC circuit is also relatively simple. In fact, it is a power frequency inductor made of a silicon steel sheet. It uses the principle that the current inside the inductor coil cannot be abruptly adjusted to adjust the phase difference between the voltage and current in the circuit, so that the current tends to be sinusoid To increase the power factor. The passive PFC structure is bulky and often has low frequency vibration and low frequency noise when working. Compared with the active PFC circuit, the power factor of the passive PFC circuit is much lower, generally only about 70%.

Power Factor Corrector Disadvantages

Therefore, the passive PFC circuit inherently has its insurmountable disadvantages:

1. As the harmonic specifications of European EN become more stringent, the quality of mass production of inductors needs to be improved, and the production difficulty will increase.

2. Heavy weight increases the risk of damage to the power supply during transportation.

3. The risk of shortage of raw materials is high.

4. If the internal structure of the power supply is incorrectly fixed, it is easy to produce vibration noise.

5. When the power supply output exceeds 300 watts, passive PFC will highlight its insurmountable defects in material cost and product performance.

Power factor corrector active

The circuit is composed of high-frequency inductors, switching tubes, and capacitors. It can be simply summarized as a step-up switching power supply circuit, which can convert 110V or 220V AC mains power to DC high voltage of about 380V. The active PFC circuit has a small size and light weight. The waveform of the current is adjusted by a dedicated IC to compensate for the phase difference between the current and voltage. Active PFC can achieve high power factor-usually more than 98%, excellent electrical performance such as wide input voltage range, but the cost is relatively high. In addition, active PFC can also be used as an auxiliary power supply. Therefore, in the use of active PFC circuits, a standby transformer is often not needed, and the ripple of the output DC voltage of the active PFC is very small. This type of power supply does not need to use large capacity filtering capacitance. Similar to the passive PFC circuit, the active PFC also generates noise when it works, but it is only high-frequency noise. Compared with passive PFC circuits, active PFC circuits are more complex and cost more than passive PFC.

Active PFC Many, mainly used in high-end power products.

Power factor corrector comparison

Power Factor Corrector Overview

1. The active PFC improves the power factor to more than 95%, and the passive PFC can only improve to about 75%. In other words, active PFC can save more energy than passive PFC.

2. The weight of power supplies using active PFC is much lighter than passive PFC products using bulky components, and the trend toward thinner and lighter products is an inevitable trend in the 3C market in the future.

Power factor corrector advantages

Compared with passive PFC, active PFC has inherent advantages:

1. The correction effect is far better than the EN harmonic specifications in Europe. Even if the specifications become more stringent in the future, they can meet the requirements.

2. As the demand for IC parts increases, costs will decrease accordingly.

3. Less risk of raw material shortage.

4. More passive professional solutions.

5. It can bring high added value of global voltage at lower cost.

6. The power factor is close to perfect 100%, which optimizes the power utilization rate and is good for environmental protection.

7. In response to the future CPU development trend, the output wattage (electricity) requirements will be higher. Active PFC has better competitiveness because the cost does not increase with the output wattage.

Overview of Power Factor Correctors

After analyzing the advantages and disadvantages of the above two mainstream power correction factors, it is self-evident that we must know that a PFC has a great impact on the performance of the power supply. Active PFC can almost 100% conversion of the input power of the power supply is nothing more than exciting data. In fact, you can do a simple calculation. If your host actually needs 250W power to consume, and the power source uses an active PFC circuit, the power factor reaches 95% of the mainstream, then the actual input power will reach 264W; if you use a passive PFC circuit, The power factor also reaches 70%, so the actual input power needs 357W. Subtracting it yields 93W, which means that a computer with active PFC can save 93W / 1000 = 0.093 degrees of power for an hour of continuous operation. Calculated according to the author's location in Guangzhou City, 0.65 yuan electricity, saving 7 cents per hour. Do not underestimate the role of seven cents. The so-called small stream can also be gathered into the sea. The same price of 400W with passive PFC Century Star Diamond 500+ and active PFC Century Star Royal Knights is 60 yuan different. about. Dividing 60 yuan and 7 cents is equal to about 857 hours, which is calculated based on the computer being turned on for about eight minutes a day. Although the power consumption saved by standby is not yet included, one hundred days can completely remove your previous money. Take it back. Obviously, if you face no one-handed action on electricity bills every month, would you think of this method of saving electricity bills? One year, two years, this is a very considerable amount in the future. This is for individuals, where are large-scale computers in enterprises, institutions or factories? Although those computers are not like Pentium D dual-core and personal tigers like SLI, but always use electricity? As a business executive or chief executive, you don't have a way to cut costs and increase revenue in your electricity bill. Moreover, it is not only Guangdong, but electricity shortages are happening all over the country. Most of China's economic development relies on low energy utilization. If energy is used as efficiently as in Europe, America or Japan, would "super-British catch up with the United States" just around the corner? As an individual, your energy conservation and consumption reduction should start from your side, to yourself, to others, and to your country.

The final content is misleading! The current meter calculates active power, and the definition of power factor is active power / (active power + reactive power). In other words, if the same main power supply is 400W, if one power factor is 0.9, the other power factor is 0.5. In practice, the meter will run equally fast (that is, the power factor is different, but the electricity rate is the same). [Electric power is counted as active power, and reactive power is actually not counted as electricity. However, the higher the power factor, the better the electrical energy utilization efficiency. For example: a host power supply with a rated power of 400W, a power factor of 0.5, and an efficiency of 90%, when it is used at full load (that is, output 400W power) The input power must be greater than 400 / 0.9 = 445W. But the power line needs a power capacity of 890V · A, because the reactive power "occupies" the power capacity of the power line although it does not do work. If the power supply with a power factor of only 0.5 is transformed to increase its power factor to 1.0, only a power line with a power capacity of 445W can be used normally. For power users, the power factor is the same, but for power plants, the same power users and the same power consumption, when the power factor of the power grid is low, more electricity will be generated. For the power supply bureau, , But need to lay thicker wires. Technically speaking, when the power factor of the grid is low, it actually means that the capacity is not fully utilized and energy is wasted. ------------- Correction: Chen Hechang