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| 型号： | FAN4802SMY |
| 厂商： | FAIRCHILD SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 0.5 A POWER FACTOR CONTROLLER WITH POST REGULATOR, 268 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | 0.150 INCH, GREEN, MS-012AC, SOIC-16 |
| 文件页数： | 7/19页 |
| 文件大小： | 577K |
| 代理商： | FAN4802SMY |
2010 Fairchild Semiconductor Corporation
www.fairchildsemi.com
FAN4800AS/CS/01S/02S Rev. 1.0.1
15
FA
N
4800A
S/C
S
/01S/02S
—
PFC/PWM
Controller
Combination
Two-Level PFC Function
To improve the efficiency, the system can reduce PFC
switching loss at low line and light load by reducing the
PFC output voltage. The two-level PFC output of the
FAN4801S/02S can be programmable.
As Figure 27 shows, FAN4801S/02S detect the voltage
of VEA and VRMS pins to determine if the system
operates low line and light load. At the second-level
PFC, there is a current of 20A through RF2 from the
FBPFC pin. The second-level PFC output voltage can
be calculated as.
()
12
2
2.5
20
FF
F
RR
Output
V
A R
R
μ
+
×
×
(3)
For example, if the second-level PFC output voltage is
expected as 300V and normal voltage is 387V,
according to the equation, RF2 is 28k RF1 is 4.3M.
The programmable range of second level PFC output
voltage is 340V ~ 300V.
Figure 27.
Two-Level PFC Scheme
Oscillator (RT/CT)
The oscillator frequency is determined by the values of
RT and CT, which determine the ramp and off-time of
the oscillator output clock:
/
1
RT CT
DEAD
f
tt
=
+
(4)
The dead time of the oscillator is derived from the
following equation:
/
1
ln
3.8
RT CT
T
VREF
tC
R
VREF
=×
×
(5)
at VREF=7.5V and tRT/CT=CT x RT x 0.56.
The dead time of the oscillator is determined using:
2.8
360
7.78
DEAD
T
V
tC
C
mA
=×
=
×
(6)
The dead time is so small (tRT/CT>>tDEAD) that the
operating frequency can typically be approximated by:
/
1
RT CT
f
t
=
(7)
Pulse Width Modulator (PWM)
The operation of the PWM section is straightforward,
but there are several points that should be noted.
Foremost among these is the inherent synchronization
of PWM with the PFC section of the device, from which
it also derives its basic timing. The PWM is capable of
current-mode or voltage-mode operation. In current-
mode applications, the PWM ramp (RAMP) is usually
derived directly from a current-sensing resistor or
current transformer in the primary side of the output
stage. It is thereby representative of the current flowing
in the converter’s output stage. ILIMIT, which provides
cycle-by-cycle current limiting, is typically connected to
RAMP
in
such
applications.
For
voltage-mode
operation and certain specialized applications, RAMP
can be connected to a separate RC timing network to
generate a voltage ramp against which FBPWM is
compared. Under these conditions, the use of voltage
feedforward from the PFC bus can assist in line
regulation accuracy and response. As in current-mode
operation, the ILIMIT input is used for output stage over-
current protection. No voltage error amplifier is included
in the PWM stage, as this function is generally
performed on the output side of the PWM’s isolation
boundary. To facilitate the design of opto-coupler
feedback circuitry, an offset has been built into the
PWM’s RAMP input that allows FBPWM to command a
0% duty cycle for input voltages below typical 1.5V.
PWM Cycle-by-Cycle Current Limiter
The ILIMIT pin is a direct input to the cycle-by-cycle
current limiter for the PWM section. Should the input
voltage at this pin exceed 1V, the output flip-flop is reset
by the clock pulse at the start of the next PWM power
cycle. When the ILIMIT triggers the cycle-by-cycle bi-cycle
current, it limits the PWM duty cycle mode and the power
dissipation is reduced during the dead-short condition.
VIN OK Comparator
The VIN OK comparator monitors the DC output of the
PFC and inhibits the PWM if the voltage on FBPFC is
less than its nominal 2.4V. Once the voltage reaches
2.4V, which corresponds to the PFC output capacitor
being charged to its rated boost voltage, soft-start begins.
PWM Soft-Start (SS)
PWM startup is controlled by selection of the external
capacitor at soft-start. A current source of 10A
supplies the charging current for the capacitor and
startup of the PWM begins at 1.5V.
相关PDF资料 |
PDF描述 |
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| FAN4801SMY | 0.5 A POWER FACTOR CONTROLLER WITH POST REGULATOR, 268 kHz SWITCHING FREQ-MAX, PDSO16 |
| FAN4801SNY | 0.5 A POWER FACTOR CONTROLLER WITH POST REGULATOR, 268 kHz SWITCHING FREQ-MAX, DIP16 |
| FAN4800CSMY | 0.5 A POWER FACTOR CONTROLLER WITH POST REGULATOR, 268 kHz SWITCHING FREQ-MAX, PDSO16 |
| FAN4800CSNY | 0.5 A POWER FACTOR CONTROLLER WITH POST REGULATOR, 268 kHz SWITCHING FREQ-MAX, DIP16 |
| FAN4802SNY | 0.5 A POWER FACTOR CONTROLLER WITH POST REGULATOR, 268 kHz SWITCHING FREQ-MAX, DIP16 |
相关代理商/技术参数 |
参数描述 |
|---|---|
| FAN4802SNY | 功能描述:电流型 PWM 控制器 PFC/PWM Controller Combination RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| FAN4803 | 制造商:FAIRCHILD 制造商全称:Fairchild Semiconductor 功能描述:8-Pin PFC and PWM Controller Combo |
| FAN4803CP1 | 功能描述:功率因数校正 IC PFC/PWM Controller Combo RoHS:否 制造商:Fairchild Semiconductor 开关频率:300 KHz 最大功率耗散: 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:SOIC-8 封装:Reel |
| FAN4803CP-1 | 制造商:FAIRCHILD 制造商全称:Fairchild Semiconductor 功能描述:8-Pin PFC and PWM Controller Combo |
| FAN4803CP1_Q | 功能描述:功率因数校正 IC PFC/PWM Controller Combo RoHS:否 制造商:Fairchild Semiconductor 开关频率:300 KHz 最大功率耗散: 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:SOIC-8 封装:Reel |
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