AND8327/D
Vdd
Vout 1
Vout 2
Rled
Slow
Lane 1
Rpullup
Fast
Lane
R2
U2B
R1
Slow
Lane 2
C1
C2
U2A
U1
TL431
R3
Primary Side
Secondary Side
Figure 19. The TL431 Wired in a Two-output Weighted Feedback Configuration
This technique offers a way to improve cross-regulation
and Figure 20 represents a simplified two-output version of
such a converter. In this 2-switch forward converter, the two
outputs (5 V and 12 V) are also coupled via their respective
output inductors. Each output contributes to 50% in the
control loop, which uses a TL431 featuring a type 2
compensation.
in a multi-output converter by affecting a weight to certain
outputs whose precision or load constraints are more
important than the others. Of course, the sum of all weight
must equal 100% at the end. In the ATX world, weighted
feedback is often encountered in the so-called Silver boxes
C4
R8
350 V
1 n
10
IRF350
D5
1N4148
L4
0.47 m
R3
47
5 V/
15 A
C1
MBR4045
M1
R11
47 k
T6
Q1
D7
R7
220 n
R2
1 k
C7
2200 m
C20
2200 m
T4
C21
1 m
10
C3
2N2907
D1
1N5818
D3
MUR460
L1
1 n
C22
220 m
D4
MUR460
R10
27
C6
470 p
IRF350
L3
0.47 m
D6
1N4148
12 V/
15 A
MBR40H100
R5
D8
R9
27
47
1 k
2N2907
M2
C19
1200 m
C8
2200 m
Q2
R12x
47 k
C5
470 p
DRV
R4
R12d
CS
FB
R13
1 k
Vdd
R100
10
1 k
R6
0.3
C7d
180 p
R101
10
R14
1 k
R31
62 k
5 k
ISO1
SFH610A
C9
100 n
R12
25.8 k
C4d
1 n
D9
TL431
C10
4.7 m
R16
10 k
VCC
Figure 20. Schematic of the Two-switch Forward Power
Supply featuring a Weighted Feedback with TL431
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12
ETC [ ETC ]
