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參數(shù)資料
| 型號： | LC5521D |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 2.5 A POWER FACTOR CONTROLLER, 18 kHz SWITCHING FREQ-MAX, DIP7 |
| 封裝： | DIP-8/7 |
| 文件頁數(shù)： | 10/40頁 |
| 文件大?。?/td> | 888K |
| 代理商： | LC5521D |
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18
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
28106.02
Figure 14. Averaged input current waveform, LC551xD series
COMP pin voltage
S/GND
EIN
Drain current
Averaged input current
1(2)
–
+
–
+
4(6)
LED
Current
sensing
resistor
S/GND
FB
C6
R7
FB pin
voltage
Gate
on-width
Gate on-width
Drain current
OSC
V
FB
OSC
PC
(LC552xF)
LC552xD
control is average current control based on the voltage mode on-
width control.
As showed in figure 16, in the average current control opera-
tion, the output current sensing resistor voltage is compared by
the operational amplifier, and its output is sent to the FB pin in
conjunction with the opto-coupler and averaged at the FB pin.
The FB pin voltage is compared against the internal oscillator
(OSC) by the FB comparator in order to control the on-width for
averaged current control operation. Here, OSC indicates the oscil-
lator circuit, which controls the minimum oscillating frequency,
quasi-resonant oscillation, and the maximum on-time limit.
The constant output current control of the output is done as below.
If the output load current becomes less than the target value,
the secondary current sensing resistor voltage will become low
and it results in low feedback current from the opto-coupler. It
causes the averaged voltage at the FB pin to become high, and
resulting in increases of the on-width and the output current.
If the output current becomes more than the target value, the
circuits operate in the opposite way The averaged voltage at the
FB pin wll become low, which reduces the on-width and the
output current.
Figure 17 shows the average input current waveform. The aver-
aged FB pin voltage becomes constant, and the duty cycle control
becomes based on the EIN voltage (C2 voltage in figures 10 and
11). It makes an averaged input current sine waveform which
realizes a high power factor.
Figure 15. FB pin peripheral circuit
3(5)
1(2)
R OCP
S/GND
4(6)
D7
FB
C6
PC1
OCP
R3
R7
LC552xD
(LC552xF)
Figure 16. On-width control, LC552xD and LC552xF series
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