HAIER LTF42K1 AND LTF47K1 POWER SUPPLY CIRCUIT WITH POWER FACTOR CORRECTION
HAIER LTF42K1 AND LTF47K1
SOME NOTES ABOUT POWER FACTOR CORRECTION (PFC)
Every year, millions and millions of notebook
computers, LCD monitors and LCD televisions are produced. With such a
fast
growing number of these and other electronic devices using more and more
power,
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 set the harmonic regulation standard on any power grid supplied
application with
power consumption over 75 watts. This essentially requires power factor
correction (PFC). Additionally, a standby power dissipation limit is set
to conserve
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 servers. 80 PLUS certifies to more
than
80% energy efficiency at 20%, 50% and 100% of rated load. To meet the
80 PLUS 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 use 80 PLUS certified
PSUs. Implementing
power factor correction (PFC) into switch mode power supplies will
maximize:
1 .The power handling capability of the power supply
2.Current handling capacities of power distribution networks Input power factor
(PF) is defined as:
PFC = REAL POWER (WATTS) / APPARENT POWER (VA )
PF is expressed 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 losses
in the power distribution network. There are two types of PFCs:
1. Active
2. Passive
Passive PFC
The simplest form of PFC is passive (Passive PFC). A passive PFC uses a filter
at the AC input to correct poor power factor. The passive PFC circuitry uses
only passive components > an inductor and some capacitors
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.
Active PFC functions include:1. Active wave shaping of the input current
2. Filtering of the high frequency switching
3. Feedback sensing of the source current for waveform control
4. Feedback control to regulate output voltage
