VB409 Ver la hoja de datos (PDF) - STMicroelectronics
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VB409 Datasheet PDF : 9 Pages
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VB409 / VB409SP
AVERAGE POWER CALCULATION IN WORST
CASE
As before explained, the device also senses the
preregulator voltage (Vcap), so that as soon as the
capacitor reaches its maximum voltage, the
trilinton reduces the current so limiting furtherly
V IN
v m ax
V1
Figure 3a
power dissipation. On the contrary if the capacitor
doesn’t reach the maximum value, the trilinton
supplies current at a steady value (Imax) during the
whole conduction angle. This is obviously the
worst case, in which the average power
dissipation is maximum.
VIN
=
Vmax
⋅
sin
(
2----π
T
⋅
t)
0
0 ≤ t ≤ -T2--
-T-
2
≤
t
≤
T
0 t1
IIN
ICL(in)
t2 T/2
T
Figure 3b
Vcap
t
ICL(in) ⋅
IIN =
0
t
0 ≤ t ≤ t1
t2
≤
t
≤
-T-
2
elsewhere
t
Assuming that
[0,t1] = [t2,T--]
2
are the conduction angles, it results:
∫ ∫ ∫ PAV = T-1- ⋅
T
(VIN ⋅ IIN)dt
=
1--
T
⋅
0
t1
T--
( VI N ⋅ ICL ( ) in) dt + 2 (V IN ⋅ I CL(in) )dt =
0
t2
∫ ∫ =
I--C---L--(--in---)--⋅---V----m---a--x
T
⋅
t1
sin(
2----π
T
⋅
t ) dt
+
T---
2
sin
(
2---π-
T
⋅
t )dt
0
t2
∫ =
I--C---L--(-i--n--)--⋅---V----m---a--x
T
⋅
2
t1
sin(
-2--π-
T
⋅
t ) dt
=
0
=
2
-I-C---L--(-i--n--)--⋅---V----m---a--x
T
⋅
--T--
2π
⋅
[–
cos
(
2---π-
T
⋅
t1)
+
cos0] =
I--C---L--(-i-n--)---⋅---V----m---a--x
π
1–
1
–
sin2
(
-2--π-
T
⋅
t1)
=
As for t1:
---V----1--
V m ax
=
sin
(
2----π
T
⋅
t1)
it follows:
PAV
=
I--C---L--(--i-n-)---⋅---V----m---a--x
π
⋅
1–
1
–
V---V-m---1a--x
2
Where
V 1 = Vr ef 1 ⋅ (1 + R-----1--)
R2
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