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AN3027 датащи(PDF) 12 Page - STMicroelectronics

номер детали AN3027
подробное описание детали  How to design a transition-mode PFC pre-regulator
PDF  41 Pages
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производитель  STMICROELECTRONICS [STMicroelectronics]
домашняя страница  http://www.st.com
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AN3027 датащи(HTML) 12 Page - STMicroelectronics

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Designing a TM PFC
AN3027
12/41
Doc ID 16134 Rev 4
If the PFC stage has to guarantee a specified hold-up time, the selection criterion of the
capacitance changes. Co has to deliver the output power for a certain time (tHold) with a
specified maximum dropout voltage (Vout min) that is the minimum output voltage value
(which takes load regulation and output ripple into account). It is also the minimum output
operating voltage threshold before triggering the “power fail” detection and consequent
stopping of the downstream system supplied by the PFC.
Equation 16
A 20% tolerance on the electrolytic capacitors has to be taken into account for the right
dimensioning. As shown in
Equation 14, for this application a capacitor C
O = 47 µF (450 V)
has been selected in order to maintain a hold-up capability of 14 ms. The actual output
voltage ripple with this capacitor is also calculated. In detail:
Equation 17
As expected the ripple variation on the output is:
Equation 18
3.3.4
Boost inductor
The boost inductor determines the operating frequency of the converter, thus it is usually
calculated so that the minimum switching frequency is greater than the maximum frequency
of the L6563S internal startup (150 µs typ.), to ensure correct TM operation. Assuming unity
PF:
Equation 19
Equation 19 demonstrates that the on-time doesn't depend on the mains phase angle, but it
is constant over the entire mains cycle.
Equation 20
ton and toff represent respectively the on-time and the off-time of the power MOSFET. ILpk is
the maximum peak inductor current in a line cycle and
θ is the instantaneous line phase of
the interval [0,
Π]). Note that the on-time is constant over a line cycle.
() 2
min
out
2
out
out
Hold
out
O
V
V
V
t
P
2
C
−
∆
−
⋅
⋅
=
() (
)
F
7
.
36
V
300
V
20
V
400
ms
10
W
100
2
C
2
2
O
µ
=
−
−
⋅
⋅
=
()
out
2
min
out
2
out
out
O
hold
P
2
V
V
V
C
t
⋅
⎥⎦
⎤
⎢⎣
⎡
−
∆
−
⋅
=
() (
)
[
]
ms
78
.
14
W
100
2
V
300
V
20
V
400
F
47
t
2
2
hold
=
⋅
−
−
⋅
µ
=
O
l
out
out
C
f
2
I
V
⋅
⋅
π
⋅
=
∆
V
02
.
18
F
47
Hz
47
2
A
25
.
0
V
out
=
µ
⋅
⋅
π
⋅
=
∆
VAC
2
IL
L
)
sin(
VAC
2
)
sin(
IL
L
)
,
VAC
(
t
pk
pk
on
⋅
⋅
=
ϑ
⋅
⋅
ϑ
⋅
⋅
=
ϑ
)
sin(
VAC
2
V
)
sin(
IL
L
)
,
VAC
(
t
out
pk
off
ϑ
⋅
⋅
−
ϑ
⋅
⋅
=
ϑ



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