Design guide IDP2303(A)
PFC design
Application Note
7
Revision 2.0
2017-05-03
3
PFC design
3.1
Target specifications
Table 2 shows the major specifications for the target PFC design.
Table 2
System specification
Parameter
Symbol
Value
Unit
Input voltage minimum
V
in_min
90
V
AC
Input voltage maximum
V
in_max
265
V
AC
Nominal bus voltage
V
bus
390
V
PFC output power
P
o_PFC
130
W
Estimated efficiency of system (PFC+LLC) at 90 V
AC
Ƞ
sys
> 87%
Estimated efficiency of PFC at 90 V
AC
ƞ
PFC
~93%
Estimated efficiency of PFC at 265 V
AC
ƞ
PFC_265
~96%
Minimum switching frequency
f
sw_min
25
kHz
Power factor
> 0.9
3.2
Power stage
A simplified application circuit for PFC stage is given in Figure 4.
Figure 4
Simplified circuit for PFC converter
3.2.1
Bridge rectifier
The total bridge power loss is calculated using the average input current flowing through two of the bridge
rectifying diodes.
𝑃
𝑟𝑒𝑐𝑡_𝑙𝑜𝑠𝑠
= 𝐼
𝑓
∗ 2𝑉
𝑓
=
2√2
𝜋
𝑃
𝑜
𝑉
𝑖𝑛_𝑚𝑖𝑛
∗ 𝜂
𝑃𝐹𝐶
90
∗ 2𝑉
𝑓
=
4√2
𝜋
130
90 ∗ 0.93
∗ 2 ∗ 0.35 = 1.96 𝑊
Knowing the value of the power loss, one can choose an appropriate bridge rectifier based on its thermal
characteristics.
