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參數資料
| 型號： | FA3647N |
| 廠商： | FUJI ELECTRIC CO LTD |
| 元件分類： | 穩壓器 |
| 英文描述： | PWM control IC with light load power saving function For Switching Power Supply Control |
| 中文描述： | 1 A SWITCHING CONTROLLER, 500 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封裝： | SOP-8 |
| 文件頁數： | 16/21頁 |
| 文件大小： | 406K |
| 代理商： | FA3647N |
FA3641P(N), FA3647P(N)
73
8. Feedback pin circuit
Figure 28 gives an example of connection in which a feedback
signal is input to the FB pin.
If this circuit causes power supply instability, connect R3 and
C4 as shown in Figure 28 to decrease the frequency gain. Set
R3 between several tens of ohms to several kilohms and C4
between several thousand picofarads to one microfarad. Be
especially careful in light load mode, in which the frequency
drops, thereby increasing the probability of power supply
instability being triggered.
9. REF characteristics
If noise is applied to the VCC pin from the outside, it may
appear at the REF pin without attenuation depending on the
noise frequency. The noise causes no problems in normal IC
operation, but must be taken into consideration when the REF
voltage is used for an external circuit. If the noise appearing at
the REF pin causes any problems, use the REF pin as shown
in Figure 29.
10. Simple voltage control on the primary side
In a flyback type power supply, the output voltages of the power
supply and auxiliary winding are almost proportional to the
number of winding turns of the transformer. This characteristic
can be used in the circuit shown in Figure 30, where the output
voltage can easily be made constant by detecting the voltage of
the auxiliary winding voltage.
However, this is an easy output voltage control method, and the
output voltage precision and regulation are therefore not as
good.
To reduce output pulse width completely to 0%, the FB pin
voltage must fall below 0.95V and R5 must be set below about
960
from the characteristics of the FB pin voltage and source
current. When using this method, also keep in mind the
characteristics of REF in item 9.
11. Disabling the overload shutdown function
As shown in Figure 31, connect a 8.2k
resistor R6 between
the FB pin and the ground. The FB pin voltage then does not
rise sufficiently high to reach the shutdown threshold voltage
when an overload occurs so that IC does not enter OFF latch
mode. Even with this connection, the overvoltage shutdown
function is available.
Since resistor R6 limits the upper voltage of the FB pin, the
maximum duty cycle may be limited to about 65%, if a 5%
precision resistor is used. To not limit the maximum duty cycle,
use a 2% or better-precision resistor for R6.
12. Polarities for overcurrent detecting and their
characteristics
The FA3641 uses positive polarity detection for overcurrent
limiting (number 3 pin of IS pin) and the FA3647 uses negative
polarity detection. The characteristics of positive and negative
polarity detection are summarized below. Select one in
accordance with the circuit used. (See item 5 in
“
Description of
each circuit.
”
)
Positive detection (FA3641)
Wiring is easy because the ground can be shared by the
main circuit and IC peripherals.
It is easy to correct the overload detecting current, which is
used to detect overload, against the input voltage.
Negative detection (FA3647)
The MOSFET drive current does not flow to the current
detection resistor and therefore it hardly affects overcurrent
detection.
Fig. 30 Simple voltage control circuit
Fig. 31 Disabling overload shutdown function
Fig. 28 FB pin circuit
Fig. 29 REF pin circuit
相關PDF資料 |
PDF描述 |
|---|---|
| FA3647P | PWM control IC with light load power saving function For Switching Power Supply Control |
| FA365 | THIN SMD HIGH-FREQUENCY CRYSTAL UNIT |
| FA-365 | THIN SMD HIGH-FREQUENCY CRYSTAL UNIT |
| FA3675F | For Switching Power Supply Control |
| FA3863X | SUPER BRIGHT LED |
相關代理商/技術參數 |
參數描述 |
|---|---|
| FA3647N-H1 | 制造商:Fuji Electric 功能描述: |
| FA3647P | 制造商:FUJI 制造商全稱:Fuji Electric 功能描述:PWM control IC with light load power saving function For Switching Power Supply Control |
| FA3647P-D1 | 制造商:Fuji Electric 功能描述: |
| FA365 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:THIN SMD HIGH-FREQUENCY CRYSTAL UNIT |
| FA-365 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:THIN SMD HIGH-FREQUENCY CRYSTAL UNIT |
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