?/DIV>
=
 
(1) 
Because  the  PWM  stage  generally  uses  a  forward 
converter,  it  is  necessary  to  limit  the  maximum  duty 
cycle  at  50%.  To  have  a  small  tolerance  of  the 
maximum  duty  cycle,  a  frequency  divider  with  toggle 
flip-flops  is  used,  as  illustrated  in  Figure  25.  The 
operation frequency of PFC and PWM stage is 1/4 of 
oscillator  frequency.  (For  FAN4800CU,  the  operation 
frequencies for PFC and PWM stages are 1/4 and 1/2 
of oscillator frequency, respectively). 
The   dead   time  for   the  PFC   gate   drive  signal   is 
determined by: 
T
D E A D
C
3 6 0
=
 
(2) 
The  dead  time  should  be  smaller  than  2%  of  the 
switching  period  to  minimize  line  current  distortion 
around the line zero crossing. 
RT /C T
V
RE F
O S C
 
T  Q
T -F F
 
T
Q
O P W M  (F A N 4 8 0 0 C U )
O P F C , O P W M
T -F F
 
Figure 25. Oscillator Configuration 
R T  / C  T
O  P  F  C
O  P  W   M
O  P  W   M    ( F  A  N  4  8  0  0  C  U  )
P  F  C    D  e  a  d  - T  i m  e
 
Figure 26. Timing Diagram 
 
I
D
 
I
D S
V
G . P F C
V
G .P W M
V
G . P F C
V
G . P W M
I
D S
I
D
 
Figure 27. Interleaved Leading / Trailing 
Edge Modulation 
Figure 27 shows the interleaved leading / trailing edge 
modulation, where the turn-off of the PFC drive signal is 
synchronized  to  the  turn-on  of  the  PWM  drive  signal. 
This technique allows the PFC output diode current to 
flow  directly  into  the  downstream  DC/DC  converter, 
minimizing the current ripple of PFC output capacitor. 
Gain Modulator 
Gain  modulator  is  the  key  block  for  the  PFC  stage 
because it provides the reference to the current control 
error amplifier for the input current shaping, as shown in 
Figure 28. The output current of the gain modulator is a 
function  of  V
EA
,  I
AC,
  and  V
RMS
.  The  gain  of  the  gain 
modulator is given as a ratio between I
MO
 and I
AC
 with a 
given V
RMS
 when V
EA
 is saturated to HIGH. The gain is 
inversely proportional to V
RMS
2
, as shown in Figure 29, 
to   implement   line   feed-forward.   This   automatically 
adjusts  the  reference  of  current  control  error  amplifier 
according to the line voltage, such that the input power 
of PFC converter is not changed  with line voltage (as 
shown in Figure 30). 
 
 
IS E N S E
IA C
V R M S
V E A
=
?/DIV>
?nbsp  -
=   ?/DIV>
-
2
(  0
.    6
)
.
M   O A
C
E
A
A
C
M
A
X
G
I
K
V
I
V    V
IE A
R  M
R
M
G a in  
M o d u la to r
R  R M  S 1
R  R M  S 2
R
R M  S 3
C  R M  S 1
C
R M  S 2
R
I A C
I A C
V
I N
I
L
x
2
k
 
Figure 28. Gain Modulator Block 
 
 
| 相關(guān)代理商/技術(shù)參數(shù) | 參數(shù)描述 | 
| FAN4800IM | 功能描述:電流型 PWM 控制器 ANG FG PFC and PWM CONTROLLER ASMC DIE RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 | 
| FAN4800IMX | 功能描述:電流型 PWM 控制器 Controller PFC - PWM Combo RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 | 
| FAN4800IN | 功能描述:電流型 PWM 控制器 ANG FG PFC and PWM CONTROLLER ASMC DIE RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 | 
| FAN4800IN_G | 功能描述:電流型 PWM 控制器 ANG FG PFC & PWM CONTROLLER ASMC DIE RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 | 
| FAN4800IN_SB82230 | 功能描述:電流型 PWM 控制器 ANG FG PFC & PWM CONTROLLER ASMC DIE RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |