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參數(shù)資料
| 型號： | FAN4800 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | Low Start-Up Current PFC/PWM Controller Combos |
| 中文描述： | 低啟動(dòng)電流式PFC / PWM控制器功放音箱 |
| 文件頁數(shù)： | 14/19頁 |
| 文件大?。?/td> | 369K |
| 代理商： | FAN4800 |
FAN4800
14
Soft Start
PWM start-up is controlled by selection of the external
capacitor at SS. A current source of 20mA supplies the
charging current for the capacitor, and start-up of the
PWM begins at 0.95V. Start-up delay can be pro-
grammed by the following equation:
where Css is the required soft start capacitance, and
the t
DELAY
is the desired start-up delay.
It is important that the time constant of the PWM soft
start allows the PFC time to generate sufficient output
power for the PWM section. The PWM start-up delay
should be at least 5ms.
Solving for the minimum value of Css:
Use caution when using this minimum soft start capaci-
tance value because it can cause premature charging of
the SS capacitor and activation of the PWM section if
V
FB
is in the hysteresis band of the V
IN
OK comparator
at start-up. The magnitude of V
FB
at start-up is related
both to line voltage and nominal PFC output voltage.
Typically, a 1.0mF soft-start capacitor will allow time for
V
FB
and PFC
OUT
to reach their nominal values prior to
activation of the PWM section at line voltages between
90Vrms and 265Vrms.
Generating Vcc
After turning on the FAN4800 at 13V, the operating
voltage can vary from 10V to 17.9V. The threshold volt-
age of the Vcc OVP comparator is 17.9V. and its hys-
teresis is 1.5V. When Vcc reaches 17.9V, PFC OUT will
be low, and the PWM section will not be disturbed.
There are two ways to generate Vcc. One way is to use
auxiliary power supply around 15V, and the other way
is to use bootstrap winding to self-bias the FAN4800
system. The bootstrap winding can be either taped
from the PFC boost choke or from the transformer of
the DC-to-DC stage.
The ratio of the bootstrap’s winding transformer for the
bootstrap should be set between 18V and 15V. A filter
network is recommended between Vcc(pin 13)and
bootstrap winding. The resistor of the filter can be set
as following.
If anything goes wrong, and Vcc goes beyond 17.9V,
the PFC gate(pin 12) drive goes low and the PWM gate
drive (pin 11) remains working. The resistor’s value
must be chosen to meet the operating current require-
ment of the FAN4800 itself (5mA, max.) in addition to
the current required by the two gate driver outputs.
EXAMPLE:
To obtain a desired VBIAS voltage of 18V, a VCC of
15V, and the FAN4800 driving a total gate charge of
90nC at 100kHz (e.g. 1 IRF840 MOSFET and 2 IRF820
MOSFET), the gate driver current required is:
Bypass the FAN4800 locally with a 1.0 mF ceramic ca-
pacitor. In most applications, an electrolytic capacitor of
between 47mF and 220mF is also required across the
part , both for filtering and as a part of the start-up boot-
strap circuitry.
CSS
tDELAY
=
A
0.95V
---------------
×
CSS
5ms
=
A
0.95V
---------------
×
100nF
=
R
FILTER
Ivcc
2V Ivcc
×
Iop
Q
PFCFET
Q
PWMFET
+
(
)
+
=
～
×
fsw
I
op
2.5mA typ
.
)
=
IGATEDRIVE
100kHz
90nC
9mA
=
×
=
RBIAS
214
–
+
-------------------------------------
=
RBIAS
ChooseRBIAS
+
=
-------------–
=
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| FAN4800_06 | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Low Start-Up Current PFC/PWM Controller Combos |
| FAN4800_10 | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Low Startup Current PFC/PWM Controller Combinations |
| FAN480001S | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:PFC/PWM Controller Combination |
| FAN48002S | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:PFC/PWM Controller Combination |
| FAN4800A | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:PFC/PWM Controller Combination |
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