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AN3142 Datasheet(PDF) 28 Page - STMicroelectronics

Part # AN3142
Description  Solution for designing a 400 W fixed-off-time controlled
PDF  44 Pages
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Manufacturer  STMICROELECTRONICS [STMicroelectronics]
Direct Link  http://www.st.com
Logo STMICROELECTRONICS - STMicroelectronics

AN3142 Datasheet(HTML) 28 Page - STMicroelectronics

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Designing a fixed-off-time PFC
AN3142
28/44
Doc ID 17005 Rev 3
at minimum mains voltage, as set in
Equation 1, guarantee against parameter variation, the
mentioned tolerances should be taken into account, making some calculations considering
the worst cases.
In this case, taking into account the resistors and threshold tolerances, 1 M
Ω and a 56 kΩ
have been calculated, therefore the actual divider ratio is 0.946. Then the following check
can be done:
Equation 55
Equation 56
Equation 57
Equation 58
Pin 11 (ZCD) is the input of the zero current detector circuit. In FOT mode, it is connected to
the Line-Modulated-Fixed-Off-Time circuit seen in
Figure 6. Taking into account the
information contained in
Section 3, the starting point for the design of that circuit is the pair
of the desired values for TOFF on the top of the line voltage sinusoid at minimum (TOFF @
VACmin) and maximum line (TOFF @ VACmax) obtained by setting the switching frequency on
the peak of the sinusoid at low mains and considering the minimum on-time of the L6563S:
Equation 59
L
_
FF
H
_
FF
L
_
FF
EN
_
RUN
ENABLE
_
FF
R
R
R
V
V
+
⋅
=
V
923
.
0
M
1
k
56
M
1
V
88
.
0
V
ENABLE
_
FF
=
Ω
Ω
+
Ω
⋅
=
multL
multL
multH
EN
_
FF
START
_
in
R
R
R
2
mV
20
V
V
+
⋅
⎟⎟⎠
⎞
⎜⎜⎝
⎛
+
=
Vac
87
k
51
k
51
M
6
.
6
2
mV
20
V
923
.
0
V
START
_
in
=
Ω
Ω
+
Ω
⋅
⎟⎟⎠
⎞
⎜⎜⎝
⎛
+
=
L
_
FF
H
_
FF
L
_
FF
DIS
_
RUN
DISABLE
_
FF
R
R
R
V
V
+
⋅
=
V
844
.
0
M
1
k
56
M
1
V
80
.
0
V
DISABLE
_
FF
=
Ω
Ω
+
Ω
⋅
=
multL
multL
multH
DIS
_
FF
STOP
_
in
R
R
R
2
mV
20
V
V
+
⋅
⎟⎟⎠
⎞
⎜⎜⎝
⎛
+
=
Vac
9
.
79
k
51
k
51
M
6
.
6
2
mV
20
V
844
.
0
V
STOP
_
in
=
Ω
Ω
+
Ω
⋅
⎟⎟⎠
⎞
⎜⎜⎝
⎛
+
=
min
sw
min
min
OFF
f
k
)
VAC
(
T
=
s
76
.
3
ns
220
kHz
80
32
.
0
)
VAC
(
T
min
OFF
µ
=
−
=



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