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參數(shù)資料
| 型號： | AN8029 |
| 廠商： | PANASONIC CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Self-excited RCC pseudo-resonance type AC-DC switching power supply control IC |
| 中文描述： | 1 A SWITCHING CONTROLLER, PSIP9 |
| 封裝： | PLASTIC, SIP-9 |
| 文件頁數(shù)： | 12/13頁 |
| 文件大?。?/td> | 132K |
| 代理商： | AN8029 |
12
AN8029
Voltage Regulators
I
Application Notes (continued)
[2] Design reference data
How to start the soft start function by external parts
The power supply rises under overload condition due to the capacitor connected to the power supply output.
In this condition, since the voltage of the power supply output is low, the normal constant voltage control attempts
to rise the power supply output at the maximum duty. The control uses the pulse-by-pulse overcurrent protection
(CLM) , attempting to limit the current. However, the pulse can not be brought down to zero due to delay of filter,
etc. As a result, a large current flows into the main switch (the power MOSFET) or the diode in the secondary
side, and in the worst case these parts are damaged. For this reason, the soft start function is used to suppress the
rush current at start of the power supply.
As shown in figure 12, the R3 and C4 are connected between the FB terminal (pin 9) and the GND terminal
(pin 5) to use the soft start function. When the supply voltage of the IC reaches the start voltage and the start
circuit begins operation, the open bias is outputted to the FB terminal.
By this voltage, the charge current flows in the C4 to
become flowing-out current of the FB terminal (I
FB
) and
output control begins under the condition in which T
ON
period is short. The I
FB
decreases with elapse of time,
since it changes proportionally to the charge current of the
C4. The CLM circuit operates, depending on the sum of
the R7 end-to-end voltage by the current which flows in
the power MOSFET at power-on and the R6 end-to-end
voltage by the charge current of the C4.
Therefore, since the current which flows in the power
MOSFET at power-on gradually increases, the rush cur-
rent can be suppressed.
GND
Start resistor
R1
V
CC
FB
V
OUT
After AC rectification
Figure 12
C8
C4
R8
C6
R6
R3
R7
CLM
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