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What's PFC? (Power Factor Correction)

Power factor is the relationship between working (active) power and total power consumed (apparent power). The ratio of true ac input power to the apparent ac input power. Essentially, power factor is a measurement of how effectively electrical power is being used. A higher power factor represents a more effective use of electrical power. Power Factor Correction on a switching power supply controls the timing and wave shape of the input current drawn to maintain the current waveform approximately in phase with and of the same shape as the line voltage. This results in a power factor of approximately 1.0. This is important when electronic equipment consumes a significant amount of power, since otherwise the facility power system could exceed its current ratings for the power consumed and potentially impact other equipment on the same power system.

In normal , electronic equipment without PFC function , the PF is around 50% only.

Why we need PFC?

The benefits of Power Factor Correction including:

1. Reduced electric utility bills ( a typical payback period is less than six months to a year)
2. Increased system capacity
3. Improved voltage

Low power factor means poor electrical efficiency. The lower the power factor, the higher the apparent power drawn from the distribution network. When low power factor is not corrected, the utility must provide the nonworking reactive power in addition to the working active power. This results in the use of larger generators, transformers, bus bars, wires, and other distribution system devices that otherwise would not be necessary. Electronic equipment with PFC could promote it-self energy utilization to help cut consumer bill in percentage , also PFC is a environment friendly technology, reducing the harmonics that creat electrical polluation to benefits the society as a whole.

How can a PFC power supply save energy?

By reducing the volt-amperes your electric utility has to deliver in order to provide a gene power level demanded by the power supply. Much less power is lost in generating useless ˇ§harmonicsˇ¨ that unnecessarily load down the AC electrical delivery system.

What is harmonics?

Harmonics are a form of noise, produced in frequencies which are a multiple of the basic 60 cycle sine wave. They are caused by switching power supplies and in other sophisticated machines, including computers and variable frequency drivers. Harmonics can distort the basic sine wave, as well as cause high currents on the neutral and ground wires in a system.

What countries are adopting the PFC requirement for electronic equipment?

January 2001, European Union have adopted the requirement for new electronic equipment that consumes more than 75 watts to meet the EN 61000-3-2 specification for harmonic content. In China, since May 1 , 2002, all electrical products used in governmental institutions must be with PFC , Japan is now developing a new project for power saving , and in the foreseeable future, the US as well , will adopt power management regulations.

What's Active / Passive PFC ?

Passive PFC, using inductor, capacitor circuitry to reduce harmonic current, because power source frequency is 50 Hz or 60Hz low frequency, it needs large inductor and capacitor. Moreover, the power factor improvement is only around 75%~80%. Active PFC , using active components(control circuit and power sine conductor On/Off switch), the fundamental working theory is to adjust input current wave-form to simulate input voltage waveform. With this method, we can achieve power factor near or equal to the 100% power factor target.

Active type power factor correction using active component (control circuit and power sine conductor ON/OFF switch). Its fundamental working theory is to adjust input current waveform to looks like input voltage waveform, this can reach the point where power factor of 1 goal. Also, the input voltage range can be 90Vdc to 264V without additional switch for choosing the voltage range. To have a universal voltage model, this power factor regulator is a very important additional value. Otherwise, the cost increased more.

Why Active PFC prior than Passive PFC?

Active PFC improves Power Factor to more than 95% , which surpasses the 75%PF with Passive PFC solution. Thus Active PFC is more energy saving than Passive PFC.
Lighter equipment will be the trend for all 3C products and PSU as well. Passive PFC PSU adopts cumbersome components which make it much heavier than an Active PFC PSU.
Benefits of Active PFC:
  Large buffer to EN harmonics requirement to ensure compliance.
  Opportunity for future cost decreases as ICs requirement volumes increase.
  Low risk in terms of material shortage.
  A more "professional" solution than Passive one.
  Full range feature comes with less cost.
  Perfect power factor approach 1 for power utilization. (Environment friendly)
  Better competition when power goes up was the trend of CPU's requirement.
Negatives of Passive PFC:
  Mass production of inductor must be accurate due to small buffer to EN harmonics limit.
  Heavy weight that might create problems during transport. (Vibration & shock)
  Possible shortage of ferrite material.
  Vibration noise if structure is not fixed correctly.
  Poor competition (cost and performance) when power up to 300W or more.

How to tell if my Power supply is with Active PFC function or not ?

Below shows some simple methods for your reference.
1.Read the statements on the power supply or its advertisment:
  Accurate rate 90%. PFC is such an useful and powerful selling point that sellers want to highline it. End users can easily find the wordings such as 'Power Factor Correct' or 'PFC' from marketing materials including retail box, user's manual, advertisement, or labels on the power supply. Since Active PFC outperforms Passive PFC, almost all power supplies with Active PFC will be pointed out the ACTIVE feature. Therefore, when a power supply with PFC function but doesn't emphize it's PFC type should be a Passive one.
2.Read the specification:
  Accurate rate 100%. The most reliable method is to check the specification of your power supply. An Active PFC power supply with the power factor (PF) more than 90% while the Passive one hardly excesses 80%. Without PFC, the normal PF is around 50%.
3.Check the back panel of a power supply:
  Accurate rate 50%. Usually the voltage input type should be full range or fixed (fixed 110V or fixed 220V) for an Active PFC PSU. That means no voltage selector. Thus if you find a voltage selector on your power supply, it imples no Active PFC function. However, this doesn't guaranty that a power supply without voltage selector will be with Active PFC. Therefore this method should apply with the above two.

Which standards do Seasonic PFC products comply to?

Seasonic's PFC products comply with CE standard of EN61000-3-2 + A1 + A2, which regulates harmonica current emissions.

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