# What is PFC?

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The PSU in my build is the Thermaltake W0069RU which is the same unit as the W0070RU except the former has the PFC function listed as 'Active', and the latter doesnt have it.. .The one with it costs 39.99, the one without costs \$44.99.. This is an excellent 430 watt psu which should be find to drive my budget gamer, only I cant decide whether its worth the 5 bucks to get the one with the PFC? Power Factor Controller, or Power Factor Correction, I cant figure out what it really does, and should I have it. help???

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silentpcreview"]POWER FACTOR CORRECTION

Increasingly, switched mode power supplies (SMPS) are designed with an active power factor correction (PFC) input stage. This is mainly to meet new regulations aimed at restricting the harmonic content of the load current drawn from power lines. Both users and power companies benefit from PFC, as does the environment.

Power Factor Correction (PFC) can be defined as the reduction of the harmonic content, and/or the aligning of the phase angle of incoming current so that it is in phase with the line voltage. Mathematically, Power Factor (PF) is equal to Real Power (Watts) divided by Apparent Power (Volt*Ampere). The basic concept is to make the input look like a pure resistor. Resistors have a power factor of 1 (unity). This allows the power distribution system to operate at maximum efficiency, which reduces energy consumption.

Non-PFC power supplies use a capacitive filter at the AC input. This results in rectification of the AC line, causes high peak currents at the crests of the AC voltage. These peak currents lead to excessive voltage drops in the wiring and imbalance problems in the three-phase power delivery system. The full energy potential of the AC line is not utilized. Nonlinear peak currents also distort output voltage and create harmonics. There is an international standard for controlling harmonics (IEC100-3-2) and PFC is mandatory for home appliances consuming 70W or more power in EU nations as of January, 2001.

PFC circuits are classified into two types: active and passive.

Passive PFC uses passive elements such as a ferrite core inductor on the input source to create a countering reactance. While easily applied to the existing power circuitry without much modification, the power factor is low (60 - 80%), the AC input must be chosen (115VAC / 230VAC), and the harmonics produced from the difference between the capacitance and the inductance are hard to control. Significant electromagnetic noise can result.

Active PFC uses switching regulator technology with active elements such as IC, FET and diodes, to create a PFC circuit This circuit has a theoretical power factor of over 95%, reduces total harmonics noticeably, and automatically adjusts for AC input voltage. However, it requires a complex EMI filter and an input source circuit, and is more costly to build.

The benefits of high PF for the user comes from the reduced AC current drawn by high PF PSUs, not in any savings from electricity bills, except in the case of commercial utility users who do pay for V(oltage) x A(mperes). There are two broad consequences:

Less stress on the AC electrical wiring: The lower current drawn by a high PF power supply means that there is less stress on the electrical wiring of the building. This can be a big plus in the case of older building with lower capacity AC wiring. It is certainly easy to see the benefits in a enterprise setting where dozens or hundreds of PCs are drawing power. If the total current load from the IT department could be reduced by 30% or more, this would be very signficant in direct electricity savings, reduced airconditioning cost, and possible avoidance of building AC re-wiring.

Lower UPS costs: Lower current draw also means that smaller capacity Uninterruptible Power Supply (UPS) units can be used. As UPS units are priced in direct proportion to their current capacity (VA), a PF of 0.98 versus one of 0.6 can traslate into a 40% reduction in purchase cost. Again, in an enterprise setting with hundreds or thousands of PCs, the savings can be very significant.

PFC Myths

There are myths about power factor correction that continue to be propagated by well-meaning people. Let's tackle the two most common ones:

Does higher PF reduce my electricity bill? No, if you are a home user. If you are an enterprise running hundreds of PCs and pay not only for power but also VA, then yes. For more details, see PFC discussion above.

Does PFC make a power supply more efficient? Not in the normal way that power supply efficiency is defined, which is the power loss (to heat) as a percentage of total AC input in AC-to-DC conversion. However, in the sense that Apparent AC power (VA) is lowered, PFC does reduce energy consumption.

Power factor correction is applied by an input circuit which uses a small amount of input power. With two PSUs that are identical, equipping one with PFC will cause a typical efficiency drop of 2~4%. Many PSUs that have Active PFC also have high efficiency, as APFC is usually found on higher quality PSUs, but the two are not intrinsically related.
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Thanks Folks.. As I proceed to read the replies and links you provided, let me throw another one at you. The pfc question came in conjunction with the Thermaltake 430 watt psu seen here:
http://www.newegg.com/product/product.asp?item=N82E1681...

But, there is another psu by FSP (Fortron) which is a 450 watt psu, AND, the main thing its got that the Thermaltake doesnt is Two +12V Rails, which Im beginning to think is something I should not do without.. See it at:
http://www.newegg.com/product/product.asp?item=N82E1681...

And lastly, in that price range is a 500 watt psu by EPower:
http://www.newegg.com/product/product.asp?item=N82E1681... also with two +12v rails

Both of the latter two do not have any PFC, but they DO have the twin +12v rails.

Which of the three psus do you prefer? If it helps answer, this is for a build based on the newegg Biostar 550 mobo/AMD Athalon dual core X2 3600+ brisbane cpu combo. Video is the 7600GT Geforce card. Its a budget gamer that will be used mostly for home office work and some minor gaming but I want the latitude to grow with it. Im using a gig of the Corsair xms DDR2 dual channle pc2 6400 ram, and will likely use some small overclocking.

thanks for the help.

A dual-rail PSU would be a wise choice indeed, the FSP would be the best of that bunch.