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AN3112 데이터시트(PDF) 17 Page - STMicroelectronics

부품명 AN3112
상세설명  Solution for designing a fixed off-time controlled PFC pre-regulator
PDF  36 Pages
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제조업체  STMICROELECTRONICS [STMicroelectronics]
홈페이지  http://www.st.com
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AN3112 데이터시트(HTML) 17 Page - STMicroelectronics

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AN3112
Designing a fixed-off-time PFC
Doc ID 16820 Rev 3
17/36
temperature), a factor of 1.75 to 2 should be taken into account. The exact factor can be
found on the device datasheet.
Now, combining equations
Equation 29 and Equation 16, the conduction losses referred to a
1
ΩRDS(on), at ambient temperature as a function of Pin and VAC can be calculated:
Equation 30
The generic switching losses due to the MOSFET commutation occurring at turn-on and
turn-off can be basically expressed by:
Equation 31
Because the switching frequency depends on the input line voltage and phase angle on the
sinusoidal waveform, it can be demonstrated that from
Equation 31 the switching losses per
1 µs of current, rise and fall-time can be written as:
Equation 32
From the STP12NM50FP datasheet trise = tfall = 0.01 µs is the crossover time at turn-on
and off.
At turn-on the losses are due to the discharge of the total drain capacitance inside the
MOSFET itself. In general, the capacitive losses are given by:
Equation 33
Where Cd is the total drain capacitance including the MOSFET and the other parasitic
capacitances such as inductor etc. At the drain node, VMOS is the drain voltage at MOSFET
turn-on.
Taking into account the frequency variation with the input line voltage and the phase angle,
the capacitive losses per 1 nF of total drain capacitance can be calculated as:
Equation 34
The total drain capacitance (Cd) of the two parallel MOSFETs is 0.36 nF, not including the
other component contributions, Vout is the drain voltage at MOSFET turn-on.
2
out
in
2
rms
cond
3
)
VAC
(
k
16
2
V
)
VAC
(
k
P
2
))
VAC
(
ISW
(
2
)
VAC
(
P
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
π
⋅
−
⋅
⋅
⋅
=
⋅
=
′
)
VAC
(
f
2
t
t
I
V
)
VAC
(
P
sw
fall
rise
MOS
MOS
switch
⋅
⎟
⎠
⎞
⎜
⎝
⎛
+
⋅
⋅
=
()
∫
π
ϑ
⋅
θ
⋅
ϑ
π
⋅
⎟⎟⎠
⎞
⎜⎜⎝
⎛
∆
−
⋅
=
′
0
sw
2
pk
max
pk
out
switch
d
)
,
VAC
(
f
sin
1
2
IL
IL
V
)
VAC
(
P
)
VAC
(
f
V
C
2
1
)
VAC
(
P
sw
MOS
2
d
cap
⋅
⋅
⋅
=
()
ϑ
⋅
ϑ
π
⋅
=
′
∫
π
d
)
,
VAC
(
f
V
1
2
1
)
VAC
(
P
0
sw
2
out
cap



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