ON Semiconductor Fairchild PFC SPM, Design Manual

Page: 9 / 19

PFC SPM
®
Design Guide
© 2005 Rev. 1.0.1-2012 Fairchild Semiconductor – System Engineering Group
8
s : j

(= j

2

f)
Control Loop Implementation
Current Loop
[Step 1]
Crossover frequency
Theoretical crossover frequency is given by following equation.
kHz
f
f
S
C
7 . 6
6
 
(Eq.3)
[Step 2]
Fz and Fp decision
kHz
f
f
C
Z
3 . 3
2
 
, kHz f f
Z P
20 6
 
[Step 3]
Rz, Cp, Cz decision
R
i
is same to R
MO
. (Refer to “other parameters” in page 10)
R
i
= 470[ Ω ],
In Eq.1,
dB
L f
R V
sL
R V
G
C
SH DC SH DC
kHz f PST
C
8 . 39 0103 . 0
) 2 ( 4 4
6 . 6
    


Therefore it requires 40dB boosting at fc(=6.6kHz).
R
z
is given by Eq.7.
dB
R
R
G
i
z
dB
40 log 20
 
 R
z
= 47[k Ω ],
From Eq.4 ,Eq.5, Cp and Cz is given.
C
p
= 180[pF], C
z
= 1[nF]
z z
z
C R
f

2
1

(Eq.4)
p z z
p z
p
C C R
C C
f

2


(Eq.5)