Although pleasantly simple and robust,a passive PFC rarely achieves low Total Harmonic Distortion (THD).Also,becau the circuit operates at the low line power frequency of 50Hz or 60Hz,the passive elements are normally bulky and heavy.Active PFC
Active PFC offers better THD and is significantly smaller and lighter than a passive PFC circuit.To reduce the size and cost of passive filter elements,an active PFC operates at a higher switching frequency than the 50Hz/60Hz line frequency.
Background
More than 90 million notebook computers,150 million LCD monitors and 50 million LCD televisions are expected to ship in 2008.With such a fast growing number of power electronics,actions must to be taken to ensure the functionality of the nationwide power grid.In 2001,the European Union put EN61000-3-2 into effect to t the harmonic regulation standard on any power grid supplied application with power consumption over 75 watts.This esntially requires power factor correction (PFC).Additionally,a standby power dissipation limit is t to conrve power when a load is OFF.“80 PLUS”is an initiative funded by electric utilities to integrate more energy efficient Power Supply Units (PSUs) - especially for desktop computers and rvers.80 PLUS certifies to more than 80% energy effi
ciency at 20%,50% and 100% of rated load.To meet the 80PLUS certification,PSUs require a PFC of 0.9 or greater at 100%load.This means PSUs that waste 20% or less electric energy (as heat at the specified load levels) will lead to reduced electricity consumption and lower bills.Rebates are sometimes given to manufacturers who u 80 PLUS certified PSUs.
Implementing power factor correction (PFC) into switch mode power supplies will maximize:
•The power handling capability of the power supply •Current handling capacities of power distribution networks
Input power factor (PF) is defined as:
PF =
Real Power (watts)Apparent Power (VA)
PF is expresd as decimal number between zero and one (0 and 1).A non-corrected power supply with a typical PF equal to 0.65 will draw approximately 1.5 times greater input current than a PFC supply (PF = 0.99) for the same output loading.The non-corrected supply requires additional AC current to be generated which is not consumed by the load,creating I 2R loss in the power distribut
ion network.
There are two types of PFCs:
新泽西爱未眠
1.Active
2.Passive
Passive PFC
The simplest form of PFC is passive (Passive PFC).A passive PFC us a filter at the AC input to correct poor power factor.The passive PFC circuitry us only passive components — an inductor and some capacitors (Figure.
1).
Power Factor Correction (PFC) Application Notes
F i g u r e 1:A passive PFC circuit requires only a few components to increa efficiency,but they are large due to operating at the line power frequency.
F i g u r e 2:An active PFC circuit produces low THD and us relatively small passive components.
大洋洲英文
Active PFC functions include:
•Active wave shaping of the input current
•Filtering of the high frequency switching
•Feedback nsing of the source current for waveform control
•Feedback control to regulate output voltage
Buck,boost,flyback and other converter topologies are ud in active
PFC circuits.
The DC-DC converter input capacitor also benefits from active PFC.
The capacitor can be sized to filter the high frequency ripple of the
active PFC circuit instead of a much larger capacitor that would be
required to smooth the 50-60Hz input.The regulated input of the DC-
DC converter also demands a lower range of duty cycle from the DC-
DC converter.Other benefits of active PFC include incread “hold-
over-time.”Hold over (brownout protection) benefits from always
starting at the maximum voltage; and becau energy in the
capacitor is related to 1/2CV2,the capacitor can be much smaller than a
capacitor in a converter without active PFC.
Boost Inductor
Inductor Selection
Cooper Bussmann Coiltronics®PFC inductors are available for u with a
wide variety of PFCs from 100W to 250W.They operate with controllers
domicilfrom veral IC manufacturers to provide PFC supply solutions that utilize
either passive or active PFC boost topology.
Coiltronics PFC inductors range from 100μH to 6.2μH,100kHz.The
standard input voltage range is 85V to 385V with different toroid materials
such as ferrite,powder iron and Kool-Mu™ to provide significant low core
loss.The toroidal geometry allows using thicker wire to decrea DC
resistance and yield higher current capacity.Many vertical or horizontal
through-hole mounting options are available with an operating temperature
range of –20°C to +105°C.
The boost-circuit bad PFC topology is the most popular.It is an
economical solution for complying with regulations.The inductance
value is lected bad on the desired current ripple in the boost
inductor.The inductance value is expresd as follows.
L =
V pK in(min) * d(max)
fs * Δidinnerparty
cnca
where:
营养师培训机构
•V pK in(min) is the peak minimum input voltage
•fs is the switching frequency
•Δi is the ripple current
•d(max) is the maximum duty cycle expresd as:
d(max) = 1- V
pK
in(min)
V o
where V o is the output voltage
The rms boost inductor current is expresd as:
IL (rms) =
I in(pk)
A
2
Fus
AC Input Line Fu
Product safety standards written by Underwriters Laboratories (UL) and the
International Electrotechnical Commission (IEC) require fus for primary AC
power protection and condary protection against any catastrophic failure
within the input filter capacitors,PFC boost module,output electrolytic
capacitors (C out) or the DC-DC converters.The PFC boost module usually
纸牌屋第2季does not contain overcurrent protection; if a short-circuit is applied across
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its output terminals,there is no internal circuit opening device to safely
interrupt the power.Without fu protection in the AC input line (e
fu F1 in Figrure 3),the boost converter is not protected.
Fusing the DC-DC converter input lines is esntial for protection against a
catastrophic DC-DC converter failure (e fus F2 and F3 in Figrure 3).
Protecting the DC-DC Converter
英文简介Although the primary input line fu will eventually activate,DC fus
positioned right at the input to the DC-DC converters will limit the energy
delivered by the hold-up capacitors (C out) and will prevent failure to the
PFC boost module.
T a b l e1:Comparison of passive and active PFC versus no PFC.
Fu time current curves (I [amps] versus t [time]) should be consulted
for verification of the primary line fu lection.The DC fu should not
open as a result of normal inrush currents flowing at supply startup.
Inrush current is limited within most PFC modules to 5A peak
(3.54A rms) by an active inrush current-limiting circuit.Inrush current
duration (t) increas with increasing output capacitance (C out) and can
be approximated by t = (50)x(C out).
Common Cooper Bussmann®fus applied to the overcurrent protection
points in the circuit of Figure 3 are:
•F1:RoHS compliant S501-2-R fast-acting 5 x 20mm ceramic tube fu
rated for 2A @ 250Vac
F i g u r e4:S501-2-R and PC-Tron Fus
Coiltronics Inductors for Power Factor Correction
The Cooper Bussmann Coiltronics®brand of magnetics specializes in standard and custom solutions,offering the latest in state-of-the-art
low-profile high power density magnetic components.We remain at the forefront of innovation and new technology to deliver the optimal mix of packaging,high efficiency and unbeatable reliability.Our
designs utilize high frequency,low core loss materials,and new and custom core shapes in combination with innovative construction and packaging to provide designers with the highest performance parts available on the market.The Coiltronics Brand product line of power magnetics continually expands to satisfy shifts in technology and related market needs.Standard Product Categories include:
• Shielded Drum Inductors• Unshielded Drum Inductors• High Current Inductors
• Toroidal Inductors• Specialty Magnetics• Custom Magnetics Plea /datasheets/elx to e data sheets on the wide variety of inductor solutions we have to offer.
For techncial inquiries e-mail
Order samples online -
•F2 & F3:RoHS compliant PC-Tron fast-acting PCB through-hole fu
rated up to 250Vac/450Vdc.(Product codes PCB,PCC,PCD,PCE,PCF,
PCH and PCI.)
Other inductors available for prower factor correction.
恭维For other inductor values and technical application assistance contact
Cooper Bussmann at
