AN2782 Datasheet, PDF (31/39 Pages) STMicroelectronics – Solution for designing a 400 W fixed-off-time controlled

AN2782
EVL6562A-400W demonstration board
Figure 23. Wide-range 400 W demonstration board electrical circuit (EVL6562A-
400W)
F1
CM-1.5mH-5A
J1
L1
8A/250V
1
R1
C1
2
1M5 470nF-X2
90 - 265Vac
+400Vdc
C14
2.2uF
C13
220nF
R14
47k
C2
470nF
C3
680nF-X2
D2
D15XB60
~
+
~
-
L3
DM-51uH-6A
C4
470nF-630V
C5
470nF-630V
D1
T
1N5406
PQ40-500uH
5-6
1-2
D3
STTH8R06
8
11
C6
470nF-630V
+400Vdc
R2
NTC 2R5-S237
C7
330uF-450V
J2
1
2
3
4
5
+400Vdc
+400Vdc
NC
RTN
RTN
R9
510k
R10
510k
R102
0R0
R11
510k
R12
R13
47K
12k
1
INV
VCC ⁸
2
7
COMP
GD
3
L6562A
6
MULT
GND
4
CS
ZCD ⁵
R3
100K
R4
100K
C11
470nF/50V
C12
100uF/50V
C15
68pF
D4
LL4148
LL4148
D6
R5
47R
C10
22N
D5
BZX85-C18
R36
3R9
R17
6R8
R35
3R9
R18
6R8
D7
LL4148
Q1
STP12NM50FP
D8
LL4148
+400Vout
Q2
STP12NM50FP
R15
R31
1k8
3k
R16
C16
30k
120pF
R19
1K0
R32
620k
R33
620k
R34
C21
10k
10nF
Q3
BC857C
R101
0R0
C20
330pF
R20
R21
R22
R23
0R47-1W 0R47-1W 0R47-1W 0R47-1W
The power stage of the PFC is a conventional boost converter, connected to the output of
the rectifier bridge D2. It includes the coil T, the diode D3 and the capacitors C6 and C7. The
boost switch is represented by the power MOSFETs Q1 and Q2. The NTC R2 limits the
inrush current at switch-on. It has been connected on the DC rail, in series to the output
electrolytic capacitor, in order to improve the efficiency during low-line operation.
Additionally, the splitting in two of output capacitors (C6 and C7) provides for managing the
AC current mainly by the film capacitor C6 so that the electrolytic can be cheaper as it has
just to bear the DC part.
At startup the L6562A is powered by the Vcc capacitor (C12) that is charged via the
resistors R3 and R4, then the T secondary winding (pins 8-11) and the charge pump circuit
(R5, C10, D5 and D4) generates the Vcc voltage powering the L6562A during the normal
operations.
The divider R32, R33 and R34 provides the L6562A multiplier with the information of the
instantaneous voltage that is used to modulate the boost current. The divider R9, R10, R11,
R12 & 13 is dedicated to sense the output. The line-modulated FOT is obtained by the
timing generator components D6, C15, R15, C16, R16, R31, Q3.
The board is equipped with an input EMI filter designed for a 2-wire input mains plug. It is
composed of two stages, a common mode Pi-filter connected at the input (C1, L1, C2, C3)
and a differential mode Pi-filter after the input bridge (C4, L3, C5). It also offers the
possibility to easily connect a downstream converter.
Doc ID 14763 Rev 2
31/39