Design Guide
41 of 48
V 1.0
2018-06-06
XDPL8218 design guide
For high power factor flyback converter with constant voltage output
Fine-tuning guide
18.3
Input power quality related parameter fine-tuning
The enhanced PFC feature can be enabled by configuring the C
EMI
parameter above zero and fine-tuning the
value to compensate for the current displacement effect, which is mainly caused by the DC link filter capacitor.
A higher C
EMI
parameter value gives higher compensation and vice versa.
The recommended starting value of the C
EMI
parameter is the value of the DC link filter capacitor C
DC,filter
placed
after the bridge rectifier. If necessary, fine-tune the C
EMI
parameter using the test configuration function in .dp
Vision, to achieve the optimized power factor and iTHD. For example with the XDPL8218 40W reference design,
the initial C
EMI
based on C
DC,filter
is 0.22
𝜇
F for powering up of the board, and fine-tuned C
EMI
= 0.2
𝝁
F parameter
is then selected for performance optimization.
In QRM1, the maximum switching frequency parameter f
sw,max
affects the number of first valley switching pulses
over every AC input half sine wave period. To lower the iTHD at high input voltage and high output power, the
number of first valley switching pulses can be reduced by lowering f
sw,max
. However, please note that the
efficiency could be reduced if the number of first valley switching pulses is reduced.
