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參數(shù)資料
| 型號： | AN-22 |
| 英文描述： | OBSOLETE when inventory is depleted. 10% tolerance no l |
| 中文描述： | 設計多路輸出電源的的TOPSwitch |
| 文件頁數(shù)： | 14/24頁 |
| 文件大?。?/td> | 569K |
| 代理商： | AN-22 |
AN-22
C
5/98
14
load regulation. The schematic of Figure 7 illustrates a simple
modification to the original circuit of Figure 4, where resistor
R6 is introduced from the 12 V output to the reference pin of
the TL431 shunt regulator.
Figure 6(b) illustrates the improvement obtained by
employing this new feedback scheme where the load
regulation on the 12 V output is improved to
±
1.5%. The
effect would be more dramatic if the transformer had greater
leakage inductance on the output windings.
The value of R6 is generally determined through iteration and
depends on the degree of feedback desired from the second
output. Introducing feedback from a second winding has a
detrimental effect on the regulation of the main output. In this
example the change in the 5 V output increases from effectively
0% in Figure 6(a) to
±
0.75% in Fig 6(b).
A good rule of thumb as a start point for tests is to choose R6
such that it yields about 10% of the current in R4 (with the
TL431 reference pin at 2.5 V).
In this example the current in R4 before modification is:
I
R
4
5
2. ) V
k
10
250
=
=
(
A
To emphasize the effect, we let the 12 V output provide 50%
of this amount through R6. Assuming that the TL431 reference
pin is still at 2.5 V
R
6
12
(
2. V
A
125
76
=
=
k
A standard resistor value of 75.0 kohm was chosen for R6 in
Figure 7.
Figure 9. Modified Schematic of Figure 4 with Isolated 30 V Output and C13 for Common Mode Current Return.
PI-2129-121197
5 V
RTN
BR1
400 V
C1
68
μ
F
400 V
C4
0.1
μ
F
U1
TOP223
R2
100
1/2 W
D2
MBR745
D3
1N4148
C10
1000
μ
F
35 V
T1
D1
BYV26C
C7*
1.0 nF
Y1
C11
120
μ
F
25 V
U2
CNY 17-2
U3
TL431
R4
10 k
R5
10 k
C9
0.1
μ
F
R1
75
VR1
P6KE200
L1
3.3
μ
H
F1
1.0 A
J1
C8
0.1
μ
F
L2
33 mH
L
N
* Two series connected, 2.2 nF, Y2-capacitors can replace C7.
D4
MUR420
L3
3.3
μ
H
D5
UF4004
C2
100
μ
F
50 V
30 V
C3
390
μ
F
35 V
C6
100
μ
F
35 V
12 V
C5
47
μ
F
D
S
C
CONTROL
R3
6.2
TOPSwitch-II
Isolated
RTN
C13
1 nF
500 V
C12
100
μ
F
50 V
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