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AN4149 Scheda tecnica(PDF) 31 Page - STMicroelectronics

Il numero della parte AN4149
Spiegazioni elettronici  Designing a CCM PFC pre-regulator based on the L4984D
PDF  43 Pages
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Produttore elettronici  STMICROELECTRONICS [STMicroelectronics]
Homepage  http://www.st.com
Logo STMICROELECTRONICS - STMicroelectronics

AN4149 Scheda tecnica(HTML) 31 Page - STMicroelectronics

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AN4149
FOT PFC boost control loop
where the unity gain factor Go is given by the following expression regardless of the control
method and the characteristics of the control IC:
Equation 86
In the previous expression Vc is the error signal of the voltage control loop (voltage on the
COMP pin for the L4984D), that is, the output of the error amplifier, and VCO the "zero-
power" level of the control voltage, that is, the burst mode threshold of COMP voltage (2.4 V,
typ.).
The effective control voltage Vcomp - VC0, can be expressed for the L4984D starting from the
expression of the variation of signal out from the modulator with respect to the E/A output
(COMP) change, using the formula indicated in the datasheet of the L4984D (equation 87).
Equation 87
Where km is the small signal multiplier gain assumed here equal to the large single gain km
(typ. 0.304). From this expression, replacing:
Equation 88
and rewriting equation 31 which describes the maximum inductor peak current as:
Equation 89
the effective control voltage Vcomp-VCO can be found:
Equation 90
Then this expression can be used to find the unity gain factor (equation 86):
o
C
C
out
out
o
C
V
V
V
P
G
⋅
−
⋅
=
)
(
0
()
2
_
4
.
2
FF
MULT
COMP
m
OFFSET
CS
CS
V
V
V
V
k
V
V
⋅
−
⋅
+
=
p
AC
FF
K
V
V
⋅
⋅
= 2
Lpk
S
CS
I
R
V
⋅
=
+
⋅
⋅
⋅
⋅
⋅
=
2
1
2
r
AC
out
out
pk
K
PF
V
V
I
IL
η
 +
⋅
⋅
⋅
⋅
=
−
2
1
2
0
r
m
in
p
S
C
COM P
K
K
P
K
R
V
V



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