Application Note 7 2008-08-01
2 Boost PFC design with ICE2PCXX
2.1 Target specification
The fundamental electrical data of the circuit are the input voltage range Vin, the output power Pout, the
output voltage Vout, the operating switching frequency fSW and the value of the high frequency ripple of the
AC line current Iripple. Table 1 shows the relevant values for the system calculated in this Application Note.
The efficiency at rated output power Pout is estimated to 91 % over the complete input voltage range.
Input voltage 85VAC~265VAC
Input frequency 50Hz
Output voltage and current 390VDC, 0.76A
Output power 300W
Efficiency >90% at full load
Switching Frequency 65kHz
Maximum Ambient temperature around PFC 70ºC
Table 1 Design parameter for the proposed design
2.2 Bridge rectifier
In order to obtain 300W output power at 85 V minimum AC input voltage, the maximum input RMS current is
A
V
P
I
in
out
RMSin 92.3
%9085
300
min_
_=
⋅
=
⋅
=
η
(1)
and the sinusoidal peak value of AC current is
AII RMSinpkin 54.592.322 __ =⋅=⋅= (2)
For these values a bridge rectifier with an average current capability of 6A or higher is a good choice. Please
note here, that due to a power dissipation of approximately
WAVIVP RMSinFBR 84.792.3122 _=⋅⋅=⋅⋅= (3)
the rectifier bridge should be connected to an appropriate heatsink. Assuming a maximum junction
temperature TJmax of 125°C, a maximum ambient temperature TAmax of 70°C, the thermal junction-to-case
RthJC of approximate 2.5 K/W and the thermal case to heatsink RthCHS of approximate 1K/W, the heatsink
must have a maximum thermal resistance of
WKRR
P
TT
RthCHSthJC
BR
AJ
BRthHS /52.315.2
84.7
70125
maxmax
_=−−
−
=−−
−
=(4)
2.3 Power MOSFET and Gate Drive Circuit
Due to the switch mode operation, the loss is only valid during the on-time of the MOSFET. The duty cycle of
the transistor in boost converters operating in CCM at minimum AC input RMS voltage is
782.0
390
85
11 min_ =−=−=
out
in
on V
V
D(5)
