AN4107 Datasheet, PDF (1/14 Pages) Fairchild Semiconductor – Design of Power Factor Correction

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Application Note AN4107
Design of Power Factor Correction Using FAN7527
1. Introduction
The FAN7527 is an active power factor correction(PFC)
controller for boost PFC application which operates in the
critical conduction mode. It turns on MOSFET when the
inductor current reaches zero and turns off MOSFET when
the inductor current meets the desired input current reference
voltage as shown in Fig. 1. In this way, the input current
waveform follows that of the input voltage, therefore a good
power factor is obtained.
1-1. Internal Block Diagram
It contains following blocks.
• Error amplifier (E/A)
• Zero current detection (Idet)
• Switch current sensing (CS)
• Input voltage sensing (MULT)
• Switch drive (OUT)
.
Inductor Peak Current
Inductor Current
Inductor Average Current
Gating
Signal
Figure 1. Inductor Current Waveform
Vcc 8
Idet 5
CS 4
MULT 3
2.5V Ref
Vcc
+
UVLO
−
Internal
Bias
12V 9V
Drive
Output
7 OUT
Timer R
6.5V
2V 1.5V
40k
8pF
+
−
Zero Current
Detector
+
−
Current Sense
Comparator
1.8V
Vm1
0 ~ 3.8V
Vmo
Multiplier
K=
Vmo
Vm1⋅ (Vm2 − Vref )
S
Q
Static OVP
R
Vref
Veao(L)=2.25V
+
2.25V
−
0.25V
−+
+
Vref
Vm2 Vref~Vref+2.5V
OVP _Isovp=30uA
Current
Detector ^Idovp=40uA
−
Vea(-)
Error Amp
1 INV
6
GND
2
EA_OUT
Figure 2. Block diagram of the FAN7527
©2001 Fairchild Semiconductor Corporation
Rev. 1.0.2
Rev. A, May 2000