MP44011 – BOUNDARY-MODE PFC CONTROLLER WITH HARMONIC INJECTION
MP44011 Rev. 1.01 www.MonolithicPower.com 13
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The turn ratio is:
R
OUT
V
n= =3
V
Then A
p
is:
P PKp RMSp
94
pew
max c
LI I
=A A = 1.27 10 mm
BKj
Where:
A
e
is the effective area of the core section;
A
w
is the effective area of the core window;
B
max
is the max swing of the magnetic flux density
(generally B
max
=0.3~0.4T);
K
c
is the window coefficient, which is about 0.3 in
design;
j is the current density of the wire, which is
typically 4-6A/mm
2
.
The EE25 core is selected according to A
p
.
The primary inductor turn number is:
pPKp
p
max e
LI
N110
BA
The needed air gap is:
2
pe
4
P
NA
6.08 10 m
L
And the secondary winding turn number is:
p
s
N
N36
n
6. MOSFET
The maximum drain voltage is:
DSmax PKmax R
V=V VΔV=685V
The maximum RMS MOSFET current is:
Qrms_max RMSp
I =I =0.53 A
And the pulse-drain current is:
Q_pulse PKp
I>I=1.51A
The FQPF8N80C (800V/8A) meets the power
requirement of the design.
7. Secondary Diode
The maximum RMS current of the output diode is:
Drms_max RMSs
I =I =1.03A
And the maximum reverse voltage is:
PKmax
Dmax OUT
V
V= V 194V
n
UF3004 (400V/3A) meets the design criteria.
8. Output Capacitor
The output capacitor is selected only based on
output voltage ripple
OUT
V
OUT 3
LVO
I
F4(K )
1
C= K 38F
2 π fF2(K)ΔV
Where K
3
=0.85.
The cap (47μF/100V) is selected as the bus
capacitor.
9. Sense Resistor
Assuming a peak value of 2.5V (@V
AC_max
=265V)
on the multiplier input, the peak value at the
minimum line voltage is V
MULTpkmin
=2.5 ×
85/265=0.8V which is multiplied by the maximum
slope of the multiplier, 1.62, giving a 1.32V peak
on the current sense. So the sense resistor will
not exceed:
sen
PKp
1.32
R0.87
I
Considering the power consumption, select a
0.4Ω sense resistor.
The first stage of flyback PFC design is complete.
Our evaluation board adds two channels of
DC/DC using the MP4689 to constitute a system
for the LED driver. For MP4689 applications,
please find MP4689 datasheet for details.
Figure 8 shows the application schematic with
power stage design. The typical performance and
circuit waveforms are shown in the typical
performance characteristics section. For more
possible applications of this device, please refer
to related Evaluation Board Datasheets.
