Datasheet
L6563 - L6563A Application information
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6.6 Inductor saturation detection (L6563 only)
Boost inductor's hard saturation may be a fatal event for a PFC pre-regulator: the current
upslope becomes so large (50-100 times steeper, see Figure 42) that during the current
sense propagation delay the current may reach abnormally high values. The voltage drop
caused by this abnormal current on the sense resistor reduces the gate-to-source voltage,
so that the MOSFET may work in the active region and dissipate a huge amount of power,
which leads to a catastrophic failure after few switching cycles.
However, in some applications such as ac-dc adapters, where the PFC pre-regulator is
turned off at light load for energy saving reasons, even a well-designed boost inductor may
occasionally slightly saturate when the PFC stage is restarted because of a larger load
demand. This happens when the restart occurs at an unfavorable line voltage phase, so that
the output voltage may drop significantly below the rectified peak voltage. As a result, in the
Figure 40. 80W, wide-range-mains PFC pre-regulator with tracking boost function active
14
3
BRIDGE
4 x 1N4007
C1
0.22 µF
400V
C3
22
m
F
25V
FUSE
4A/250V
R3
68 k
Ω
T
11
12
L6563
13
2
1
C6 100 nF
R6
10
Ω
MOS
STP8NM50
4
C6
56 µF
400V
Vo=200 to 385 V
Po=80W
Vac
(88V to 264V)
R7a,b
0.68
Ω
1/4 W
R9
47.5 k
Ω
+
-
C2
2.2nF
D1
STTH1L06
NTC
R5
62 k
Ω
C5
1 µF
5
C4
470 nF
6
7
10
8
9
R4
21 k
Ω
R8b
1 M
Ω
Supply Voltage
10.3 to 22V
R8a
1 M
Ω
C7
10 nF
R10b
3.3 M
Ω
R10a
3.3 M
Ω
R11
34.8 k
Ω
R1b
3.3 M
Ω
R1a
3.3 M
Ω
R2
51.1 k
Ω
R10
390 k
Ω
Figure 41. Tracking boost and voltage feedforward blocks
R1
L6563
L6563A
INV
1
Vout
TBO
6
1:1 CURRENT
MIRROR
R
T
2.5V
E/A
+
-
COMP
2
3V
-
+
5
I
TBO
I
R1
MULT
3
R5
Rectified mains
R6
"ideal"
diode
MULTIPLIER
1/V
2
current
reference
R2
I
R2
I
TBO
9.5V
9.5V
VFF
C
FF
R
FF