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參數(shù)資料
| 型號(hào)： | SC4911 |
| 廠商： | Semtech Corporation |
| 英文描述： | Bias/Primary Side PWM Controller with Ultra Low Start-up Current |
| 中文描述： | 偏置/小學(xué)側(cè)PWM控制器與超低啟動(dòng)電流 |
| 文件頁(yè)數(shù)： | 7/14頁(yè) |
| 文件大?。?/td> | 228K |
| 代理商： | SC4911 |
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7
2006 Semtech Corp.
www.semtech.com
SC4911
POWER MANAGEMENT
Typical Applications
48V TO 12V FLYBACK CONVERTER AS AUXILIARY
SUPPLY
Figure 2
shows a simple bias supply using the SC4911.
This 36 - 72V input flyback power supply employs primary
side regulation from the transformer bias winding, which
eliminates the need of opto coupler and secondary
reference error amplifier. This is best for low cost
applications requiring isolation and narrow load variation
range on the secondary.
During the start-up, the input source trickle charges the
capacitor C1 through start-up resistor R1. As long as
voltage across C1 reaches the Vcc turn-on threshold,
the SC4911 turns on abruptly and start driving the gate
of MOSFET Q1. After the SC4911 starts up the primary
bias winding supplies the primary circuitry.
The output of the T1 bias winding is rectified, filtered by
C1 and is fed to the FB through feedback resistor R5
and R7. The output voltage on the secondary is
proportional to the bias voltage by the turns ratio of the
output to the bias winding. C7 and R9 are for frequency
compensation. An additional small capacitor could be
used from COMP to GND if it is needed. The LUVLO pin
monitors the input voltage via resistor R2 and R4 to
determine turn-on and turn-off of the converter. Capacitor
C5 helps filter out the noise from the input line.
Figure 2. 48V to 12V Flyback Converter as Auxiliary Supply
R1
100K
C7
47nF
Vin = 48V
Vpri = 12V
R4
100K
R2
2.7MEG
C5
100pF
R9
4.7K
C8
1000pF
D1 1N5819
Vo = 12V
Q1
Si2320DS
U1 SC4911
1
2
3
4
5
6
7
8
LUVLO
RT
FB
COMP
ILIM
GND
OUT
VCC
T1
3
5
8
10
2
1
R8
1.00
C3
10uF
D2 1N5819
R7
100K
R5
383K
R3
68
R6
51
C4
0.1uF
C6
150pF
C1
10uF
C2
100uF
R10
100K
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|---|---|
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