Wheelman [PT]
19-03-2004, 08:39
Cá vai mais um testamento:teeth:
Fonte: Power Factor Correction : Correction Required! (http://www.rojakpot.com/default.aspx?location=3&var1=84&var2=0)
Power Factor Correction or PFC is the latest buzzword to be thrown around by power supply companies. Something they are making quite a lot of fuss about. And why not? There are very few features that differentiate one power supply from another.
Now, a lot has been said about PFC. Unfortunately, many of the explanations are either confusing or misleading. That's why we thought we would take a shot at clearing up the confusion.
What Is PFC?
First, let's take a look at what some manufacturers are saying about PFC. Here is a quote from Zalman :-
"In a conventional power supply with switching regulators, a rectifying circuit that converts an AC input source into a DC source for the primary circuit is used. In this rectifying circuit, a capacitor with a large capacitance is used to soften transient response and reduce ripple so that the switching regulator is not over-stressed.
However, the peak charge of the capacitor becomes greater with greater capacitance, and this leads to non-linear bursts of peak over-current into the primary circuit. Such peaks of current distort output voltage, create harmonic frequencies, and reduce power factor.
There is now 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."
And here is a cryptic explanation by Enermax :-
"the utility PF rate =95% @ 230Vac at full rated load. From January 1, 2001, two standards¡mEN61000-3-2 (power line harmonics) and EN61000-3-3 (power line flicker)¡ngo into full effect to all EC countries. All products shipped to EC countries or placed on the market in this area must be compliant to these standards."
Confusing, isn't it? Well, let's clear up the confusion.
PFC Revealed!
As you all know, AC power is a power source with alternating voltage and current. For AC power to be useful, the voltage and current must be in the same phase. If there is misalignment of the phase angle of the AC voltage and current's sine waves, then it must be corrected before the AC power can be used.
In Non-PFC power supplies, a capacitive filter that consists of capacitors is used to rectify the phase misalignments. However, such filters cause very high current flow at the peak of every AC sine wave crest. This current surge causes a sudden voltage drop in the power supply's AC source and disturbs the power company's AC line.
This reduces the energy potential of the AC line. In other words, the percentage of usable AC power that can be provided by the power company's AC line is effectively reduced. This is why PFC is so important to the power company. Hence, the new EU regulation making PFC mandatory in all home appliances consuming power of 70W or more.
The high peak currents also increase the amount of EMI (Electromagnetic Interference) and RFI (Radio Frequency Interference) produced by the power supply. The power supplies we use today are actually switching power supplies that discharge power 50 to 100 thousand times a second to the computer. Such rapid switching by itself creates a lot of EMI and RFI. Add in the high peak currents from the AC source and you will have greatly increased EMI and RFI.
For the consumer, the increased EMI and RFI are usually no more than a nuisance, and then only when an electrical or electronic appliance is affected. But the EMI and RFI also affect the AC line and the noise has to be dissipated by the power company. It is not something they enjoy doing.
This is where PFC comes in. PFC is the method by which the high peak current and harmonics on the output voltage are reduced. The advantages of PFC are reduced EMI/RFI and a cleaner AC line with increased energy potential, both of which are far more advantageous to power companies than the consumer.
With that said, the future lies with PFC. There is no denying that increased efficiency should be the goal, even if there is little benefit as such to the consumer.
PFC Types
There are two types of Power Factor Correction - Passive PFC and Active PFC.
Passive PFC uses passive elements like a ferrite core inductor on the AC input. It is very easy to implement in existing power circuits although the power factor is low at 60-80%. The proper AC input voltage (115V or 230V) must also be chosen manually. In addition, significant EMI can still result with a 115V AC source. Of course, a 230V AC source will not have this problem!
Active PFC, on the other hand, uses a switching regulator with active elements like an IC, FETs (Field Effect Transistors) and diodes to create an active PFC circuit. This circuit allows the power supply to achieve a power factor of up to 95%, significantly reduce harmonics and automatically adjusts the AC input voltage. This means you do not have to manually select the AC input voltage. It works with all voltages from 110V to 240V.
Conclusion
To summarize, a power supply without PFC circuitry will have a power factor of approximately 60% or lower. It will also create a considerable amount of harmonic distortion. A power supply with PFC circuitry improves the power factor to 75-95% with greatly reduced harmonic distortions.
But please note that the power factor has nothing to do with power efficiency. One should not be misled into thinking that PFC is a miracle feature that boosts a power supply's efficiency from 60% to 95%, thereby saving you a lot of money in electricity bills. It's just not going to happen.
Right now, most, if not all, high-end power supplies come with PFC circuitry to meet EU standards, particularly if the manufacturer has a presence in Europe. Of course, there are still plenty of cheap, non-PFC power supplies in the market. But eventually, all power supplies will come with PFC circuitry. If not Active PFC, then the cheaper Passive PFC.
So, while PFC is a good thing to have, it is not something you want to throw too much money at. Not only are certain manufacturers hyping PFC up to differentiate their products from rival products; they are also charging a lot for it too. Therefore, it is important that you be aware of what PFC is all about.
We hope that this article will be of some help to you when you are looking for a PFC power supply. With so many misleading statements about Power Factor Correction, it is important to be forewarned so that you will have a better idea of how much you should pay for PFC support in your power supply.
Fonte: Power Factor Correction : Correction Required! (http://www.rojakpot.com/default.aspx?location=3&var1=84&var2=0)
Power Factor Correction or PFC is the latest buzzword to be thrown around by power supply companies. Something they are making quite a lot of fuss about. And why not? There are very few features that differentiate one power supply from another.
Now, a lot has been said about PFC. Unfortunately, many of the explanations are either confusing or misleading. That's why we thought we would take a shot at clearing up the confusion.
What Is PFC?
First, let's take a look at what some manufacturers are saying about PFC. Here is a quote from Zalman :-
"In a conventional power supply with switching regulators, a rectifying circuit that converts an AC input source into a DC source for the primary circuit is used. In this rectifying circuit, a capacitor with a large capacitance is used to soften transient response and reduce ripple so that the switching regulator is not over-stressed.
However, the peak charge of the capacitor becomes greater with greater capacitance, and this leads to non-linear bursts of peak over-current into the primary circuit. Such peaks of current distort output voltage, create harmonic frequencies, and reduce power factor.
There is now 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."
And here is a cryptic explanation by Enermax :-
"the utility PF rate =95% @ 230Vac at full rated load. From January 1, 2001, two standards¡mEN61000-3-2 (power line harmonics) and EN61000-3-3 (power line flicker)¡ngo into full effect to all EC countries. All products shipped to EC countries or placed on the market in this area must be compliant to these standards."
Confusing, isn't it? Well, let's clear up the confusion.
PFC Revealed!
As you all know, AC power is a power source with alternating voltage and current. For AC power to be useful, the voltage and current must be in the same phase. If there is misalignment of the phase angle of the AC voltage and current's sine waves, then it must be corrected before the AC power can be used.
In Non-PFC power supplies, a capacitive filter that consists of capacitors is used to rectify the phase misalignments. However, such filters cause very high current flow at the peak of every AC sine wave crest. This current surge causes a sudden voltage drop in the power supply's AC source and disturbs the power company's AC line.
This reduces the energy potential of the AC line. In other words, the percentage of usable AC power that can be provided by the power company's AC line is effectively reduced. This is why PFC is so important to the power company. Hence, the new EU regulation making PFC mandatory in all home appliances consuming power of 70W or more.
The high peak currents also increase the amount of EMI (Electromagnetic Interference) and RFI (Radio Frequency Interference) produced by the power supply. The power supplies we use today are actually switching power supplies that discharge power 50 to 100 thousand times a second to the computer. Such rapid switching by itself creates a lot of EMI and RFI. Add in the high peak currents from the AC source and you will have greatly increased EMI and RFI.
For the consumer, the increased EMI and RFI are usually no more than a nuisance, and then only when an electrical or electronic appliance is affected. But the EMI and RFI also affect the AC line and the noise has to be dissipated by the power company. It is not something they enjoy doing.
This is where PFC comes in. PFC is the method by which the high peak current and harmonics on the output voltage are reduced. The advantages of PFC are reduced EMI/RFI and a cleaner AC line with increased energy potential, both of which are far more advantageous to power companies than the consumer.
With that said, the future lies with PFC. There is no denying that increased efficiency should be the goal, even if there is little benefit as such to the consumer.
PFC Types
There are two types of Power Factor Correction - Passive PFC and Active PFC.
Passive PFC uses passive elements like a ferrite core inductor on the AC input. It is very easy to implement in existing power circuits although the power factor is low at 60-80%. The proper AC input voltage (115V or 230V) must also be chosen manually. In addition, significant EMI can still result with a 115V AC source. Of course, a 230V AC source will not have this problem!
Active PFC, on the other hand, uses a switching regulator with active elements like an IC, FETs (Field Effect Transistors) and diodes to create an active PFC circuit. This circuit allows the power supply to achieve a power factor of up to 95%, significantly reduce harmonics and automatically adjusts the AC input voltage. This means you do not have to manually select the AC input voltage. It works with all voltages from 110V to 240V.
Conclusion
To summarize, a power supply without PFC circuitry will have a power factor of approximately 60% or lower. It will also create a considerable amount of harmonic distortion. A power supply with PFC circuitry improves the power factor to 75-95% with greatly reduced harmonic distortions.
But please note that the power factor has nothing to do with power efficiency. One should not be misled into thinking that PFC is a miracle feature that boosts a power supply's efficiency from 60% to 95%, thereby saving you a lot of money in electricity bills. It's just not going to happen.
Right now, most, if not all, high-end power supplies come with PFC circuitry to meet EU standards, particularly if the manufacturer has a presence in Europe. Of course, there are still plenty of cheap, non-PFC power supplies in the market. But eventually, all power supplies will come with PFC circuitry. If not Active PFC, then the cheaper Passive PFC.
So, while PFC is a good thing to have, it is not something you want to throw too much money at. Not only are certain manufacturers hyping PFC up to differentiate their products from rival products; they are also charging a lot for it too. Therefore, it is important that you be aware of what PFC is all about.
We hope that this article will be of some help to you when you are looking for a PFC power supply. With so many misleading statements about Power Factor Correction, it is important to be forewarned so that you will have a better idea of how much you should pay for PFC support in your power supply.