參數(shù)資料
型號： ML4813
廠商： Fairchild Semiconductor Corporation
元件分類： 基準(zhǔn)電壓源/電流源
英文描述： Flyback Power Factor Controller(倒轉(zhuǎn)功率因數(shù)控制器)
中文描述： 反激式功率因數(shù)控制器（倒轉(zhuǎn)功率因數(shù)控制器）
文件頁數(shù)： 11/15頁
文件大?。?/td> 265K
代理商： ML4813
ML4813
11
f
SWITCH
(kHz)
sin
2
1
k
r
r
p
=
ê
r
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
167
250
333
417
500
583
667
750
833
917
1000
1083
1167
1250
1333
1417
1500
1583
1667
9.1
11.2
12.9
14.4
25.8
17.1
18.3
19.4
20.4
21.4
22.4
23.3
24.2
25.0
25.7
26.5
27.3
28.0
28.9
The output voltage "rides" on the input voltage when the
(+) output is measured with respect to PWR GND as
shown in Figure 10.
The extra op amp provided in the ML4813 can be used to
sense the output voltage for regulation and overvoltage
conditions. This op amp is connected as a difference
amplifier with its output referenced to PWR GND.
Resistors RH1, RH2, RL1, RL2 are used to scale down the
voltage.
Normally, RH1 = RH2 = RH and RL1 = RL2 = RL. The
voltage designated as V
S
in Figure 7 is given by:
V
V
RL
+
RH
RL
S
OUT
=
(16)
The output capacitance should be calculated such that it
has the required output ripple at the worst case operating
point. In addition, the ESR should be sufficiently low to
prevent excessive dissipation due to RMS currents. The
first criterion can be met by choosing the value of the
output capacitor based on the following:
C
P
V
f
V
OUT
IN
L
R
OUT
2
p
D
(17)
Where:
C
OUT
= Total output capacitance
P
IN
= Total input power
D
V
R
= Peak output capacitor ripple voltage
f
L
= Line frequency times 2 (120 for 60Hz line)
The second criterion for the selection of the output
capacitor can be satisfied by choosing a component with
adequately low ESR value that can safely bypass the RMS
currents.
OUTPUT DIODE
The output diode can be a "fast" or ultrafast' type
depending on the operating frequency. Reverse recovery
losses are low since under normal operating conditions,
the regulator operates in discontinuous current mode. The
diode should be rated to handle the maximum output
current. The resulting power dissipation will be the
forward drop of the diode times the output current.
POWER SWITCH
If a power MOSFET is used, it should be sized for the
required efficiency. Lower R
DS(ON)
devices will yield
lower losses, but if they are operated at high frequencies
(100kHz), higher charge dumping losses will be
experienced. The RMS current value through the power
FET and the sensing resistor is:
I
L
424
.
I
f
V
k
r
RMS
P
L
RMS
=
=
ê
3
2
1
sin
p
(15)
APPLICATIONS
(Continued)
Where:
I
RMS
= Total RMS current through the power MOSFET
f
L
= Line frequency times 2 (120 for 60Hz line)
r = f
SWITCH
/f
L
Table 1 is provided to assist in calculating (18). When the
power switch is a bipolar transistor (constant V
CE
drop),
then the power dissipation produced can be calculated
by:
P
P
V
V
D
IN
RMS
CE
=
09
(19)
Where:
P
D
= Power dissipation in the transistor
V
RMS
= RMS value of the minimum input voltage
V
CE
= Forward drop of the power transistor
Figure 10. Output Voltage with Respect to PWR GND
V
TIME
PWR GND
200V
VOUT
VOUT+
VOUT-
Table 1. Constants for Calculating IRMS (Equation 18)
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