LM3450AEV230V30/NOPB National Semiconductor, LM3450AEV230V30/NOPB Datasheet - Page 12

• Manufacturer Part Number: LM3450AEV230V30/NOPB
• Description: LM3450A EVAL BOARD 230V30
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3450AEV230V30/NOPB

• Current - Output / Channel: 700mA
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 50V
• Features: -
• Voltage - Input: 180 ~ 265VAC
• Utilized Ic / Part: LM3450A
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

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PFC BACKGROUND
Power factor (PF) is a number between 0 and 1 that indicates
how well energy is transmitted from input to output of a sys-
tem. It can be described by average power (P
voltage (V
Or by distortion factor (K
(K
With a purely resistive system, PF = 1. The addition of reactive
elements necessary in any converter, such as EMI filters and
energy storage, will induce some amount of displacement
(phase shift between the input voltage and input current). The
addition of switching devices will also create distortion (ener-
gy present in the harmonics relative to the switching frequen-
cies). These non-idealities decrease the PF towards zero.
Active power factor correction attempts to make the input
impedance look as resistive as possible to the power source.
Since the output of the converter is usually a regulated voltage
or current, there is a need for large energy storage elements
to remove the twice line frequency (100Hz or 120Hz) ripple.
A power factor control architecture, as shown in
very little capacitance at the input. Instead, the twice line fre-
DISP
):
RMS
), and RMS current (I
DIST
) and displacement factor
RMS
):
FIGURE 2. PFC System Architecture
Figure
AVG
), RMS
2, has
12
quency content is removed with large energy storage capac-
itance at the output.
With minimal input capacitance, the converter is able to pro-
vide two important functions at the same time:
•
•
The PFC control approach requires two separate control
loops to achieve both functions: a fast loop which shapes the
input current, and a slow loop that regulates the output volt-
age.
The fast control loop shapes the input current to have the
same sinusoidal shape as the AC input voltage. Assuming
both are perfect sinusoids with zero distortion or phase shift,
the power factor will be perfect (unity). Unfortunately, distor-
tion is always present in switching converters. An input filter,
which is required to comply with EMI standards, helps to at-
tenuate the switching content, thereby reducing distortion.
However, the added filter capacitance will increase the phase
shift at the same time. Though perfect PF is not achievable
within real applications, extremely high PF (>.99) is possible
using most active PFCs.
The output voltage has to be regulated slowly to ensure the
converter ignores the twice line frequency ripple present on
the output. Therefore, the voltage loop containing the error
amplifier should have a bandwidth at least an order of mag-
nitude slower (<20Hz is common). Sometimes the bandwidth
is increased to improve transient response, which is the case
with off-line dimmable LED drivers. Though PF decreases
with the increase in bandwidth, high PF (>.95) is still possible.
Shape the input current
Regulate the output voltage
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