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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(shè)計多路輸出電源的的TOPSwitch |
| 文件頁數(shù)： | 15/24頁 |
| 文件大?。?/td> | 569K |
| 代理商： | AN-22 |
C
5/98
AN-22
15
Note that since the sum of the currents through R4 and R6 is a
constant equal to 2.5V divided by R5, the additional feedback
that R6 introduces from the 12 V output will tend to reduce the
regulated value of the 5 V output. This requires that R4 is in
turn adjusted to retain the 5 V output at the desired level. To
retain the voltage at the reference pin of the TL431 at 2.5 V, the
value of R4 must therefore be increased to reduce its current by
50%.
R
4
5
2. V
250 125
20
=
(
(
)
=
A
k
A slightly larger precision 21.0 kohm resistor was specified in
the circuit of Figure 7 to compensate for the small penalty in
regulation on the 5 V output.
Figure 8 shows load regulation measurements before and after
these circuit modifications with the 5 V output load held
constant at 1 A and the 12 V output load varied from 10% to
100%. In Figure 8(a), the 5 V output is very stable since this
is exclusively providing output feedback, while the 12 V
output drops by 4% over the load range. In Figure 8(b), the
introduction of R6 maintains tighter regulation on the 12 V
output (
±
1.5% variation with load), whereas this additional
feedback introduces a
±
0.75% variation in the 5 V output
voltage over the same load range.
The degree of feedback required from each output can thus be
determined depending on the application requirements for
output voltage tolerance. Breadboard evaluation is necessary
to adjust component values for the desired performance.
EMI Considerations
In general, the EMI considerations in a multiple output
TOPSwitch
power supply do not differ from those of a single
output supply, and are covered in detail in AN-15. There are,
however, specific multiple output power supplies where
Figure 10. Modified Schematic of Figure 4 with Soft-Start Capacitor C15 Added.
5 V
RTN
BR1
400 V
C1
68
μ
F
400 V
C4
0.1
μ
F
U1
TOP223
R2
100
1/2 W
D8
MBR745
D3
1N4148
C2
1000
μ
F
35 V
T1
D1
BYV26C
C7*
1000 pF
250VAC
Y1
C3
120
μ
F
35 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
C12
47
μ
F
50 V
30 V
C11
120
μ
F
35 V
C6
100
μ
F
50V
12 V
C5
47
μ
F
D
S
C
CONTROL
R3
5.2
TOPSwitch-II
C10
470
μ
F
35 V
PI-2132-121897
C15
22
μ
F
25 V
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