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參數(shù)資料
| 型號： | AN8027 |
| 廠商： | PANASONIC CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | AC-DC switching power supply control IC with standby mode |
| 中文描述： | 1 A SWITCHING CONTROLLER, 80 kHz SWITCHING FREQ-MAX, PSIP9 |
| 封裝： | PLASTIC, SIP-9 |
| 文件頁數(shù)： | 14/28頁 |
| 文件大小： | 301K |
| 代理商： | AN8027 |
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AN8027, AN8037
Voltage Regulators
14
I
Application Notes (continued)
[1] Operation descriptions (continued)
5.
Soft start (continued)
As shown in figure 6, connect R3 and C4 between the
FB pin (Pin 9) and GND pin (Pin 5) so that the switching
regulator will be in soft start operation. When the voltage
supplied to the IC reaches the start voltage and the opera-
tion of the startup circuit begins, an open bias voltage of
approximately 6.4 V is output to the FB pin. As a result,
the charge current I
FB
flows into C4 from the FB pin. Then
the switching regulator starts up at high V
FB
, thus per-
forming output control while the T
ON
period is short. The
voltage difference between both edges of C4 rises accord-
ing to the time constant determined by R3 and C4, thus
decreasing I
FB
with the lapse of time and increasing the
T
ON
period gradually.
The above operation increases the flow of current to
the power MOSFET gradually after the switching regula-
tor is turned on, thus suppressing the inrush current. How-
ever, this reduces the transient response of the feedback
loop, so care is required in designing this circuit.
Notes on selecting R3
The oscillation circuit of this IC is designed under the condition that the T
ON
period is definite. If excessively
low resistance value for R3 is selected, the slope of the triangular wave on the CF pin immediately after the
startup may become extremely steep, leading to malfunction of the oscillation circuit. Accordingly, we rec-
ommend that you adjust R3 so that the drive pulse width t
1
immediately after the startup is 0.5 ms or greater.
(Refer to figure 7.)
Note that the drive pulse width t
1
depends on the capacitance value of the C
CF
that is connected to the CF
pin (Pin 3). Figure 8 indicates recommended values of R3 corresponding to the capacitance value C
CF
.
(In actual mounting conditions, the correlation shown in figure 8 may deviate slightly.)
AN8027, AN8037
C8
PC1
R3
C4
C6
R8
R7
Figure 6
V
CC
GND
Rectified AC
To AC
CLM
Out
FB
Startup resistor
R1
t
1
V
OUT
(Pin 6)
CF
(Pin 3)
Start
Figure 7
Figure 8
10
0
12
14
18
20
16
22
3 000
R3 (k
)
C
2 000
1 000
V
CC
=
16 V
C4
=
0.033
μ
F
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